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  Linux NET-2/NET-3 HOWTO
  Terry Dawson, [e-mail]
  v3.3, 13 August 1995

  This document aims to describe how to obtain, install and configure
  the Linux NET-2 and NET-3 networking software. Some answers to some of
  the more frequently asked questions are included in the appendix. This
  document is not designed to teach you about tcp/ip networking, though
  some information of this kind is included where possible. Pointers to
  other documentation which does teach tcp/ip networking principles are
  listed.

  1.  Introduction.

  This is the Linux NET-2-HOWTO. This document is a complete rewrite of
  the earlier NET-FAQ and of the subsequent NET-2-HOWTO versions 1.0+.
  This document is for the new NET-2 and NET-3 tcp/ip networking code
  for Linux kernels 1.0 and above.


  1.1.  Changes from the previous release.


  Additions:
          Appletalk - thank you Cees de Groot.
          IP_MASQUERADE - Thank you Ken Eves.
          ipalias - thanks Patrick Ashmore, [e-mail]
          More ISDN information

  Corrections/Updates:
          Updated V.35 information, thank you Matti Aarnio.





  1.2.  A brief development history of Linux Networking.

  Ross Biro <[e-mail]> wrote the original kernel based
  networking code for Linux. He used ethernet drivers written by Donald
  Becker <[e-mail]>, a slip driver written by
  Laurence Culhane <[e-mail]>, and a D-Link driver by
  Bj0rn Ekwall <[e-mail]>.

  The further development of the Linux networking code was later taken
  up by Fred van Kempen <[e-mail]>, who took Ross's code and
  produced the NET-2 release of network code. NET-2 went through a
  number of revisions until release NET-2d, when Alan Cox
  <[e-mail]> set about debugging the Fred's code with
  the aim of producing a stable and working release of code for
  incorporation into the standard kernel releases. This code was called
  originally called NET-2D(ebugged), and was incorporated into the
  standard kernel releases some time before Linux vers 1.0 was released.

  PPP support was added by Michael Callahan, <[e-mail]>
  and Al Longyear, <[e-mail]>, originally as patches to the
  kernel, and in later releases as part of the standard kernel
  distribution.

  With the release of Linux vers 1.0, Linus made a decision to continue
  supporting Alan's code as the standard network kernel code.

  The latest version of the code, NET-3, appears in kernel releases
  1.1.5 and later, and is essentially the same code, but with many
  fixes, corrections and enhancements.

  Alan has added such features as IPX and AX.25 modules.  Florian La
  Roche, <[e-mail]> has produced an updated distribution of
  network applications.

  NIIBE Yutaka has enhanced the PLIP driver.

  Jonathan Naylor has taken up development work on the AX.25 code and
  has added many features including NetRom support.

  Many other people have made contributions by way of bug fixes, ports
  of applications and by writing device drivers.


  2.  Disclaimer.

  The Linux networking code is a brand new implementation of kernel
  based tcp/ip networking. It has been developed from scratch, and is
  not a port of any existing kernel networking code.

  Because it is a fresh implementation it may still have a number of
  bugs or problems with it, and there may be a number of fixes and
  patches released.  If you are worried about problems then just stick
  to the version of network code released with the standard kernel
  releases and utility sets. These standard kernel releases are denoted
  by an even number in the second digit, 1.2.7 for example is a
  production release. The kernel versions with an odd number as the
  second digit are alpha versions and you should expect to find problems
  or bugs with these version as they are test releases.  The networking
  code has a small team of dedicated people working on it, with a cast
  of thousands testing the code, collecting and reporting bugs and
  problems, providing fixes for problems. Any problem you experience is
  likely to have already been reported, and be being worked on, and will
  possibly be corrected soon, so be patient, or if you can help, offer
  your assistance.

  We do not, and cannot, know everything there is to know about the
  Linux network software. Please accept and be warned that this document
  probably does contain errors. Please read any README files that are
  included with any of the various pieces of software described in this
  document for more detailed and accurate information. We will attempt
  to keep this document as error-free and up-to-date as possible.
  Versions of software are current as at time of writing.

  NOTE: While its name may appear similar to the Berkeley Software
  Distribution NET-2 release, the Linux network code actually has
  nothing at all to do with it. Please don't confuse them.


  3.  Questions already ?

  `The only stupid question is the unasked one.'

  If you have general configuration questions, and you have been unable
  to find the answers after reading the other various HOWTO and FAQ
  files, then you would be best served to post them to
  comp.os.linux.networking, or, if you believe your question to be
  specifically related to the Linux Network code, then you could post it
  to the NET mailing list. Please include as much relevant information
  as possible, there is nothing more annoying than to have a bug or
  problem reported without sufficient information to even begin
  searching for it.

  Version numbers and revisions of code, a detailed account of the
  problem, and the circumstances that caused it to occur, are essential.
  Trace and debug messages where available should also be considered
  mandatory.
  If you have a question relating to the configuration of, or problems
  experienced with, any linux distribution, regardless of who has
  provided it, please contact the people who created the distribution
  first before attempting to report the problem to the network code
  developers. The reason for this is that some of the distributions use
  non-standard directory structures, and supply test/non-standard
  versions of code and utilities. The developers of the NET-2 code
  cannot be expected to offer support for the network code as
  distributed in any form, other than as described in this document, or
  as per distributed Alpha test instructions.

  To join the Linux linux-net channel on the mail list server, send mail
  to:


       [e-mail]

       with the line:

       subscribe linux-net

       as the message body and you will be subscribed. The subject line is ignored.




  Remember, keep in mind that the linux-net channel is for development
  discussions only.

  A PPP list has been established. To join it, use the same procedure as
  for joining the linux-net channel, except specify linux-ppp in place
  of linux-net in the message body.

  Note also that a linux-hams list has been established. This list has
  been established for the discussion of programs related to Amateur
  Radio. To join it, follow the same procedure as for joining the liux-
  net or linux-ppp channels, except specify linux-hams in linux-net in
  the message body.


  4.  Related Documentation. (Where to learn about tcp/ip)

  If you are looking for information about tcp/ip networking that this
  HOWTO does not cover, then you might try the following sources, as
  they provide some very useful information.

  Olaf Kirch has written a substantial document as part of the Linux
  Documentation Project entitled the Linux Network Administration Guide.
  This is an excellent document. It covers all aspects of setting up and
  using the tcp/ip networking under Linux, including NFS, UUCP, mail,
  News, nameserver etc.

  Olaf's book supplements this HOWTO, taking up where this document
  leaves off. This document covers the installation and configuration of
  the NET code, i.e. `How to put your machine on the net'. If you are
  new to unix networking, then I strongly urge you to obtain a copy and
  read it first. It will answer a lot of questions for you that are not
  within the scope of this document.

  The current release version is available in:

  sunsite.unc.edu


       /pub/Linux/docs/linux-doc-project/network-guide/*

  There are various versions of the document in this directory. The most
  common formats are supported, being plain ascii, Postscript, DVI,
  Latex and groff.

  The Linux Network Administrators Guide is Copyright (c) by Olaf Kirch.

  There are now quite a variety of companies publishing Linux
  documentation so if you want to avoid having to retrieve and print the
  document yourself you should have little trouble finding Olaf's book
  in a bound form over the counter at any good bookshop.

  You should also read the other HOWTO documents relevant to networking
  with Linux.

  They are:

  The Ethernet-HOWTO <http://sunsite.unc.edu/mdw/HOWTO/Ethernet-
  HOWTO.html>, which you should read if you intend using an ethernet
  card with Linux. It includes a lot of detail on how to select, install
  and configure an ethernet card for Linux and on how to diagnose
  problems related to the ethernet driver.

  The PPP-HOWTO <http://sunsite.unc.edu/mdw/HOWTO/PPP-HOWTO.html> if you
  intend using ppp.

  The Serial-HOWTO <http://sunsite.unc.edu/mdw/HOWTO/Serial-HOWTO.html>
  if you intend using slip or ppp in server mode.

  The NIS-HOWTO <http://sunsite.unc.edu/mdw/HOWTO/NIS-HOWTO.html> if you
  are interested in running a version of Sun's Network Information
  Service.

  The HAM-HOWTO <http://sunsite.unc.edu/mdw/HOWTO/HAM-HOWTO.html> if you
  are interested in configuring and running amateur radio software.

  The Mail-HOWTO <http://sunsite.unc.edu/mdw/HOWTO/Mail-HOWTO.html> and
  the News-HOWTO <http://sunsite.unc.edu/mdw/HOWTO/News-HOWTO.html> for
  some specific information on setting up Mail and News on your system.

  The UUCP-HOWTO <http://sunsite.unc.edu/mdw/HOWTO/UUCP-HOWTO.html> if
  you will be connecting to the net via UUCP.

  The Firewall-HOWTO <http://sunsite.unc.edu/mdw/HOWTO/Firewall-
  HOWTO.html> if you want to build a Linux based Firewall gateway for
  your network.

  If you are after some basic tutorial information on tcp/ip networking
  generally, then I recommend you take a look at the following
  documents:


     tcp/ip introduction
        text version <ftp://athos.rutgers.edu/runet/tcp-ip-intro.doc>,
        postscript version <ftp://athos.rutgers.edu/runet/tcp-ip-
        intro.ps>.

     tcp/ip administration
        text version <ftp://athos.rutgers.edu/runet/tcp-ip-admin.doc>,
        postscript version <ftp://athos.rutgers.edu/runet/tcp-ip-
        admin.ps>.

  If you are after some more detailed information on tcp/ip networking
  then I highly recommend:



  "Internetworking with TCP/IP"
  by Douglas E. Comer

  ISBN 0-13-474321-0
  Prentice Hall publications.




  If you are wanting to learn about how to write network applications in
  a Unix compatible environment then I also highly recommend:



       "Unix Network Programming"
       by W. Richard Stevens

       ISBN 0-13-949876-1
       Prentice Hall publications.





  4.1.  New versions of this document.

  If your copy of this document is more than two months old then I
  strongly recommend you obtain a newer version. The networking support
  for Linux is changing very rapidly with new enhancements and features,
  so this document also changes fairly frequently. The latest released
  version of this document can always be retrieved by anonymous ftp
  from:

  sunsite.unc.edu


       /pub/Linux/docs/HOWTO/NET-2-HOWTO

       or:

       /pub/Linux/docs/HOWTO/other-formats/NET-2-HOWTO{-html.tar,ps,dvi}.gz




  or via the World Wide Web from the Linux Documentation Project Web
  Server <http://sunsite.unc.edu/mdw/linux.html>, at page: NET-2-HOWTO
  <http://sunsite.unc.edu/mdw/HOWTO/NET-2-HOWTO.html> or directly from
  me, <[e-mail]>. It will also be posted to the
  newsgroups: comp.os.linux.networking, comp.os.linux.answers, and
  news.answers from time to time.

  You can find news.answers FAQ postings, including this one, archived
  on rtfm.mit.edu:/pub/usenet.


  4.2.  Feedback.

  Please send any comments, updates, or suggestions to me,
  <[e-mail]>. The sooner I get feedback, the sooner I
  can update and correct this document. If you find any problems with
  it, please mail me instead of posting to one of the newsgroups, as I
  may miss it.



  5.  Some terms used in this document.

  You will often see the terms client and server used in this document.
  They are normally fairly specific terms but in this document I have
  generalised their definitions a little so that they mean the
  following:

     client
        The machine or program that initiates an action or a connection
        for the purpose of gaining use of some service or data.

     server
        The machine or program that accepts incoming connections from
        multiple remote machines and provides a service or data to
        those.

  These definitions are not very reliable either, but they provide a
  means of distinguishing the ends of peer to peer systems such as slip
  or ppp which truly do not actually have clients and servers.

  Other terms you will see are:


     IP address
        This is a number that uniquely identifies a TCP/IP host on the
        network. The address is 4 bytes long and is usually represented
        in what is called the "dotted decimal notation", where each byte
        is represented in decimal from with dots `.' between them.

     Hardware address
        This is a number that uniquely identifies a host in a physical
        network at the datalink layer. Examples of this are Ethernet
        Addresses or AX.25 Addresses.

     datagram
        A datagram is a discrete package of data and headers which
        contain addresses, which is the basic unit of transmission
        across an IP network. You might also hear this called a
        `packet'.

     MTU
        The Maximum Transmission Unit (MTU) is a parameter that
        determines the largest datagram than can be transmitted by an IP
        interface without it needing to be broken down into smaller
        units. The MTU should be larger than the largest datagram you
        wish to transmit unfragmented. Note, this only prevents
        fragmentation locally, some other link in the path may have a
        smaller MTU and the datagram will be fragmented there. Typical
        values are 1500 bytes for an ethernet interface, or 576 bytes
        for a SLIP interface.

     MSS
        The Maximum Segment Size (MSS) is the largest quantity of data
        that can be transmitted at one time. If you want to prevent
        local fragmentation MSS would equal MTU-IP header.

     window
        The window is the largest amount of data that the receiving end
        can accept at a given point in time.

     route
        The route is the path that your datagrams take through the
        network to reach their destination.

     ARP
        This is an acronym for the  Address Resolution Protocol and this
        is how a network machine associates an IP Address with a
        hardware address.


  6.  NET-2/NET-3 Supported functionality.

  The NET code is a complete kernel based implementation of tcp/ip for
  Linux.


  6.1.  General Support

  The recent NET-2 and NET-3 versions of code support:

     Ethernet Cards
        most popular ethernet cards are supported. Including some
        portable, pocket adaptors and PCI.

     SLIP (Serial Line IP) and PPP (Point to Point Protocol)
        for tcp/ip networking over serial lines such as the telephone
        via modem, or a local cable between two machines.

     Van Jacobsen Header Compression
        for compressing the tcp/ip headers to improve slip/ppp
        performance over low speed lines.

     PLIP (Parallel Lines IP)
        to allow local connections between two machines using your
        printer ports.

     EQL Load balancing
        allows you to use two (or more) links to connect your machine to
        another machine or the Internet (provided your ISP supports it)
        to effectively double your bandwidth. New release kernels
        support this.

     NFS (Networked File System)
        to allow you to remotely mount another machines filesystems
        across a network connection.

     IPX (Novell)
        to allow you to write custom IPX applications, or to use Linux
        as an IPX router.

     Sun's Network Information System - NIS
        An NIS implementation has been ported to Linux should you wish
        to use it.

     Amateur Radio Support
        A number of features for Amateur Radio Operators are now
        supported.

     ARCNet
        An ARCNet driver has been written and is included in recent
        kernels. It might not be as fast as ethernet but the cards are
        much cheaper.

     IBM's Token Ring
        to allow linux to be installed on a Token Ring lan. An
        experimental Token Ring driver has been written is included in
        recent kernels.

     Appletalk
        Or is this EtherTalk ? Either way, I think this will let you
        shares files and printers with your Macintosh. See `Experimental
        and Developmental modules.'  below.
     WaveLan Wireless Lan Card support
        to allow you to operate your linux machine in a mobile fashion
        or at some distance from your network. Support for the WaveLan
        Wireless lan card is now included in recent kernels.

     ISDN
        There is some experimental support for some proprietry ISDN
        cards available. See `Experimental and Developmental modules.'
        below.

     ATM
        There is a team of programmers working to provide ATM support
        for Linux.

     IP firewalling
        to assist in configuring your Linux machine as a secure firewall
        gateway.

     IP Accounting
        to allow you to keep track of who is using how much of your
        network.

  The NET-2 and NET-3 network code does not yet currently support:


     SPX/NCP (Novell Netware) support
        to allow Linux to serve and mount Novell network filesystems or
        use Novell prinetd. This is being worked on but due to the
        proprietry nature of the product it may take some time to do.

     FDDI
        There is currently no support that I know of for FDDI cards for
        Linux.

     System-V streams
        there is a team of people working on System-V streams for Linux,
        details are presented later.


  6.2.  Supported Ethernet cards.

  The 1.2.0 linux kernel release supports the following types of
  Ethernet cards:


  o  WD80*3 and close compatibles.

  o  SMC Ultra.

  o  AMD LANCE and PCnet (AT1500 and NE2100) and close compatibles.

  o  3Com 3c501 (obselete and very slow).

  o  3Com 3c503.

  o  3Com 3c505.

  o  3Com 3c507.

  o  3Com 3c509/3c579.

  o  Cabletron E21xx.

  o  DEPCA and close compatibles.


  o  EtherWorks 3.

  o  ARCNet.

  o  AT1700 (not clones).

  o  EtherExpress.

  o  NI5210 and close compatibles.

  o  NI6510.

  o  WaveLAN.

  o  HP PCLAN+ (27247B and 27252A).

  o  HP PCLAN (27245 and other 27xxx series).

  o  NE2000/NE1000 and close compatibles.

  o  SK_G16.

  o  Ansel Communications EISA 3200.

  o  Apricot Xen-II on board ethernet.

  o  DE425, DE434, DE435.

  o  Zenith Z-Note.

  o  AT-LAN-TEC/RealTek pocket adaptor.

  o  D-Link DE600 pocket adaptor and close compatibles.

  o  D-Link DE620 pocket adaptor and close compatibles.

  Later versions of the Kernel software may support a wider variety of
  cards.

  If you intend using and ethernet card with Linux you should read the
  Ethernet-HOWTO <ftp://sunsite.unc.edu/pub/Linux/docs/HOWTO/Ethernet-
  HOWTO> as it contains a lot of very useful information on the
  supported ethernet cards, including information on how to choose an
  ethernet card if you are intending to puchase some specifically for
  Linux.

  As mentioned above, Linux supports other means of network connection
  if you don't have access to an ethernet card or connection. Many
  universities and businesses worldwide offer some form of dial-up
  network access. Generally these forms of access will offer an option
  of either SLIP or PPP access, so you will be well catered for. All you
  will need is a telephone modem, the one you already have may well be
  good enough, and to configure your Linux system appropriately. There
  are sections below that describe exactly what you need.


  6.3.  Support for Amateur Radio

  Linux now supports a number of features specifically for Amateur
  Radio. The latest alpha kernels are now distributed with standard
  support for:


     AX.25 Support
        Alan Cox and Jonathan Naylor have kernel based AX.25 socket
        support working.
     Netrom Support
        Jonathan Naylor is developing kernel based NetRom support. It is
        still experimental but is progressing well and is available for
        testing.

     Ottawa PI Card
        A mature driver for the Ottawa PI card has been developed by
        Dave Perry of the Ottawa Packet Radio Group.

     Generic SCC card driver
        A generic driver for SCC cards is now included in alpha kernels
        developed by Joerg Reuter.

  Further detail on the Amateur Radio support can be found in the HAM-
  HOWTO <http://sunsite.unc.edu/mdw/HOWTO/HAM-HOWTO.html>.



  7.  Getting the NET-2/NET-3 software.

  Before you can configure the networking software you must obtain all
  of the bits and pieces that make it up. These include the current
  version of the kernel code (version 1.0 or later), the correct system
  libraries, the tcp/ip configuration programs and files (e.g.
  /sbin/ifconfig, /etc/hosts etc.), and finally a set of network
  application programs (such as telnet, ftp, rlogin etc.).

  If you obtained Linux from a distribution you may already have all
  that you need. Check and make sure that you do. For example, some
  Linux distributions come with all of the network configuration files,
  binaries, libraries, and kernel installed, so there's no reason to get
  the following files.

  NOTE: they may be in directories and files different to those
  specified in this HOWTO document

  If you DO have the network software, skip to the `Configuring the
  kernel' section. If you DO NOT have the network software follow the
  following directions.


  7.1.  The kernel source.

  Version 1.2.0 of the Linux kernel is the production version. Any of
  the Linux kernels after that release are enhancements or bug fixes. If
  you feel at all concerned about the possibility of having to patch and
  modify the kernel source, then you should stick to this release, as it
  will do most of what you want it to. In the case of the networking
  code though, I strongly suggest you just take a deep breath and follow
  the newer releases of code, as there have been many changes in the
  newer version kernels that affect networking. I know you hear it from
  everyone and everywhere, but when trying out any new version of kernel
  software you should always ensure that you have sufficient backups of
  your system just in case something goes seriously wrong while you are
  testing.

  The current kernel version is found in:

  ftp.funet.fi


       /pub/OS/Linux/PEOPLE/Linus/v1.2/linux-1.2.0.tar.gz




  This is a gzipped file, so you will need gzip to uncompress it.

  To install it, try:



       # cd /usr/src
       # mv linux linux.old
       # gzip -dc linux-1.2.0.tar.gz | tar xvf -




  You may also find some files called  patch-1.2.1.gz ... in the same
  directory. These are patch files. If you have a linux kernel that is
  version 1.2.1 then what this means is that you have linux kernel
  version 1.2.0 with patch 1 applied. So you don't need to patch 1. If
  there are any patch files that are greater than the version of kernel
  you have, you should obtain all of those above, and apply them in
  sequence with something like the following commands:



       # cd /usr/src
       # for patchfile in .../patch*
       > do
       > gzip -dc $patchfile | patch -p0 2>>patch.errs
       > done

        ...




  Check the output file (patch.errs) and search for the string fail.  If
  you can't find it then all of the patch files were applied ok. If it
  is there, then at least one of the patch files didn't apply correctly.
  If this happens what you should do is start again from a clean kernel
  archive and apply the patches one by one until you find the patch file
  that failed. If you can't work out why it didn't work then report it
  as a problem.


  7.2.  The libraries.

  You'll want at least version 4.4.2 of libc, as there were problems
  with earlier version that affected subnet masks.

  The current libraries (libc-4.6.27) can be found in:

  sunsite.unc.edu


       /pub/Linux/GCC/




  You will need at least the following files:


  o  image-4.6.27.tar.gz

  o  inc-4.6.27.tar.gz


  o  extra-4.6.27.tar.gz

  o  release.libc-4.6.27

  When installing libc.4.6.27 you MUST read release.libc-4.6.27 before
  you install the libraries. Please note that to use release 4.5.26 or
  later you will also need at least GCC version 2.6.2, and Linux kernel
  1.1.52 or later.


  7.3.  The network configuration tool suite.

  You will need the utility suite that provides tools to configure your
  network support.

  The current NET-2 utility suite is available from:

  sunacm.swan.ac.uk


       /pub/misc/Linux/Networking/PROGRAMS/NetTools/net-tools-1.1.95.tar.gz




  Because the kernel networking code is still changing some changes to
  the network tools have been necessary as new kernels are released, so
  you will need to choose the version that is appropiate for the kernel
  version you intend to use.

  The filenames reflect the earliest version of kernel that the tools
  will work with. Please choose the filename whose version equals, or is
  less than the version of kernel source you intend to use.

  To build and install the tools, you should try:


       # cd /usr/src
       # mkdir net-tools
       # cd net-tools
       # gzip -dc net-tools-1.1.95.tar.gz | tar xvf -
       # make




  This will automatically run the Configure.sh script. If everything
  makes ok, then:



       # make install




  If you use a kernel version 1.1.26 or earlier you should look in:

  sunacm.swan.ac.uk


       /pub/misc/Linux/Networking/PROGRAMS/Other/net032/




  In this directory you will find three versions of the network tools.
  The following table lists net-032 package name with the relevant
  kernel versions:



       net-0.32d-net3.tar.gz     1.1.12+
       net-0.32b.tar.gz          1.1.4+
       net-0.32.old.tar.gz       pre 1.1.4 kernels




  These packages include the essential network configuration programs
  such as ifconfig, route, netstat etc. These will be discussed later.


  7.4.  The network applications.

  You will want a number of network application programs. These are
  programs like telnet, ftp, finger and their daemons at least. Florian
  La Roche, <[e-mail]> has put together a fairly complete
  distribution of network applications in both binary and source form.
  The tcp/ip application binaries and some sample config files are found
  in:

  ftp.funet.fi


       /pub/OS/Linux/PEOPLE/Linus/net-source/base/NetKit-A-0.08.bin.tar.gz
       /pub/OS/Linux/PEOPLE/Linus/net-source/base/NetKit-B-0.06.tar.gz




  If there are newer versions then use the newer versions. Please read
  the README file first just to make sure that you have the necessary
  prerequisites.

  Florian used to have a binary distribution of the networking
  applications (the B file) available but it is no longer there, so you
  will have to build the files yourself. You can use the following
  procedure:



       # cd /usr/src
       # gzip -dc NetKit-B-0.06.tar.gz | tar xpvlf -
       # cd NetKit-B-0.06




  Then, read the README file. You will need to edit the Makefile and set
  the HAVE_SHADOW_PASSWORDS define appropriately. I don't use shadow
  passwords, so I commented it out by placing a # at the start of the
  line. The rest should not need modifying, so then all you should have
  to do is:



       # make
       # make install



  IMPORTANT NOTE: Florian has built and prepackaged these tar files for
  your convenience. Florian has attempted to make them as complete as
  possible and has included a distribution of the binaries found in the
  net-tools-n.n.nn releases. Unfortunately Florian has chosen not to use
  the same directory structure as Alan did when he prepared the
  installation script for the net-tools. This will mean that you should
  be very careful when installing them. Florian will change this later
  so that this difference is not a problem, but until then, I suggest
  you do the following instead of the above:



       -  Unpack the binaries somewhere safe:
       # cd /usr/src
       # mkdir NetKit
       # cd NetKit
       # gzip -dc NetKit-A-0.07.bin.tar.gz | tar xpvlf -
       # gzip -dc NetKit-B-0.06.bin.tar.gz | tar xpvlf -

       -  Remove Florians copies of the network tools previously described:
       # rm ./bin/hostname ./sbin/route ./sbin/ifconfig ./sbin/netstat
       # rm ./usr/sbin/arp ./usr/sbin/rarp ./usr/sbin/slattach

       -  Copy Florian's files into their new home:
       # cp -vrpd . /





  7.5.  Additional drivers or packages.

  If you want to add some developmental, or Alpha/Beta test code, such
  as AX.25 support, you will need to obtain the appropriate support
  software for those packages. Please check the relevant sections for
  those packages in this document for more detail.


  8.  Configuring the kernel.

  Before you can use any of the network tools, or configure any network
  devices, you must ensure that your kernel has the necessary network
  support built into it. The best way of doing this is to compile your
  own, selecting which options you want and which you don't.

  Assuming you have obtained and untarred the kernel source already, and
  applied any patches that you might need to have applied to get any
  nonstandard or developmental software installed, all you have to do is
  edit /usr/src/linux/drivers/net/CONFIG. This file has many comments to
  guide you in editing it, and in general you will need to edit very
  little, as it has sensible defaults. In my case I don't need to edit
  it at all.  This file is really necesary if your ethernet card is an
  unusual one, or is one that isn't automatically detected by the
  ethernet driver. It allows you to hard code some of the elements of
  your ethernet hardware. For example, if your ethernet card is a close,
  but not exact clone of a WD-8013, then you might have to configure the
  shared memory address to ensure the driver detects and drives the card
  properly. Please check the The Ethernet-HOWTO
  <ftp://sunsite.unc.edu/pub/Linux/docs/HOWTO/Ethernet-HOWTO> for more
  definitive information on this file and its effect on ethernet cards.
  This file also contains configurable parameters for PLIP, though the
  defaults should again be ok unless you have a particularly slow
  machine.

  When you are happy that the CONFIG file is suitable for your purposes,
  then you can proceed to build the kernel. Your first step will be to
  edit the top level Makefile to ensure the kernel will be built with
  the appropriate VGA settings, and then you must run the kernel
  configuration program:



       # cd /usr/src/linux
       # make config




  You will be asked a series of questions. There are four sections
  relevant to the networking code. They are the General setup,
  Networking options, Network device support, and the Filesystems
  sections. The most difficult to configure is the Network device
  support section, as it is where you select what types of physical
  devices you want configured. On the whole you can just use the default
  values for the other sections fairly safely. The following will give
  you an idea of how to proceed:



       *
       * General setup
       *
        ...
        ...
       Networking support (CONFIG_NET) [y] y
        ...
        ...




  In the General setup section you simply select whether you want
  network support or not. Naturally you must answer yes.



       *
       * Networking options
       *
       TCP/IP networking (CONFIG_INET) [y]
       IP forwarding/gatewaying (CONFIG_IP_FORWARD) [n]
       IP multicasting (CONFIG_IP_MULTICAST) [n]
       IP firewalling (CONFIG_IP_FIREWALL) [n]
       IP accounting (CONFIG_IP_ACCT) [n]
       *
       * (it is safe to leave these untouched)
       *
       PC/TCP compatibility mode (CONFIG_INET_PCTCP) [n]
       Reverse ARP (CONFIG_INET_RARP) [n]
       Assume subnets are local (CONFIG_INET_SNARL) [y]
       Disable NAGLE algorithm (normally enabled) (CONFIG_TCP_NAGLE_OFF) [n]
       The IPX protocol (CONFIG_IPX) [n]
       *




  The second half of the Networking options section allows you to enable
  or disable some funky features that you can safely accept the defaults
  on until you have some idea why you want to change them. They are
  described briefly later if you are interested.

       *
       *
       * Network device support
       *
       Network device support? (CONFIG_NETDEVICES) [y]
       Dummy net driver support (CONFIG_DUMMY) [n]
       SLIP (serial line) support (CONFIG_SLIP) [y]
        CSLIP compressed headers (CONFIG_SLIP_COMPRESSED) [y]
        16 channels instead of 4 (SL_SLIP_LOTS) [n]
       PPP (point-to-point) support (CONFIG_PPP) [y]
       PLIP (parallel port) support (CONFIG_PLIP) [n]
       Do you want to be offered ALPHA test drivers (CONFIG_NET_ALPHA) [n]
       Western Digital/SMC cards (CONFIG_NET_VENDOR_SMC) [y]
       WD80*3 support (CONFIG_WD80x3) [y]
       SMC Ultra support (CONFIG_ULTRA) [n]
       AMD LANCE and PCnet (AT1500 and NE2100) support (CONFIG_LANCE) [n]
       3COM cards (CONFIG_NET_VENDOR_3COM) [n]
       Other ISA cards (CONFIG_NET_ISA) [n]
       EISA, VLB, PCI and on board controllers (CONFIG_NET_EISA) [n]
       Pocket and portable adaptors (CONFIG_NET_POCKET) [n]
       *




  This section is the most important, and the most involved. It is where
  you select what hardware devices you want to support. You can see that
  I have selected SLIP support with header compression, PPP, the WD80*3
  driver, and nothing else. Other options will appear depending on what
  you select. If you answered `n' to the `SLIP..' option you not be
  presented with the compressed slip or 16 channel options. Simply
  answer `y' to whatever you want to play with, and `n' to those that
  you don't.



       *
       * Filesystems
       *
        ...
        ...
       /proc filesystem support (CONFIG_PROC_FS) [y]
       NFS filesystem support (CONFIG_NFS_FS) [y]
        ...
        ...




  If you wish to run an NFS client then you will want to include the NFS
  filesystem type. You will need to include the /proc filesystem because
  a number of the network utilities use it.

  After you have completed the configuration, all that remains is to
  actually compile the kernel:



       # make dep
       # make




  Don't forget to make zlilo if the new kernel compiles and tests ok.

  8.1.  What do all those funky Networking options actually do?

  Newer kernels have a number of options that you are asked about when
  you do a make config. Generally you will not need to change these, but
  some of the options might be useful to you in certain circumstances.


     TCP/IP networking
        This one is obvious, it selects whether you configure the tcp/ip
        suite of protocols into your kernel. Chances are if you are
        reading this then you will want to answer `y' to this one.

     Dummy networking device
        This was added to allow slip and PPP users to configure an
        address on their linux machine that would not be dependent on
        their serial link being established. It is an easy way to give
        your linux machine two addresses.

     IP forwarding/gatewaying
        This determines what your kernel will do when it receives a
        datagram that has a destination address that is not one of its
        own devices. You must have this option selected if you want your
        kernel to act as an IP router. Most SLIP and PPP servers will
        want this option selected.

     IP multicasting
        This is alpha test code support for IP multicasting, examples of
        which include services such as `Internet Talk Radio' and live
        video. You will need additional programs to make use of this
        facility, this is just the kernel support.

     IP firewalling
        This option allows you to provide flexible security options for
        your linux machine. You can selectively enable/disable access to
        tcp/ip ports from any address ranges you choose. This also needs
        additional programs to support it.

     IP accounting
        This option is for those people that want to use their Linux
        machine to provide internet connectivity to others on a
        commercial basis. It allows you to count and record incoming and
        outgoing bytes on a per port and address basis. With the
        addition of suitable software this would allow you to produce
        seperate usage charges for each person using your systems
        networking capabilities.

     PC/TCP compatibility mode
        This option provides a work-around for a bug that causes
        problems when using the PC/TCP networking programs to talk to
        your linux machine. There is a PC/TCP bug which provokes a
        difficult to remedy Linux bug, and this option prevents the two
        clashing. Normally you would leave this disabled, but if you
        have users on your network who use PC/TCP then you may have to
        enable this option to prevent problems.

     Reverse ARP
        This option allows you to configure the RARP protocol into your
        kernel. This option was added to allow the booting of Sun 3
        systems. This is not generally very useful otherwise.

     Assume subnets are local
        This option selects whether you assume that your whole subnet is
        directly connected to your linux machine, or whether it might be
        bridged or otherwise subdivided at a lower layer. In practise it
        will make little difference if you leave it set at the default.

     Disable NAGLE algorithm
        This is a timing option that determines when a datagram should
        be transmitted. The default setting provides for the best
        throughput in most situations and you should leave this set as
        it is, as disabling it will degrade your throughput. This option
        can be selectively changed from within a program with a socket
        option, and you would normally be much better off leaving it set
        at the default and specifically writing your programs to disable
        the NAGLE algorithm if they require extremely fast
        interactivity.

     The IPX protocol
        This option selects whether you compile the IPX protocol support
        into your kernel. The IPX protocol is an internetworking
        protocol similar in function to the IP protocol. This protocol
        is one of those used by the Novell suite.

     Amateur Radio AX.25 Level 2
        This option selects whether you compile in the Amateur Radio
        AX.25 protocol suite. If you select this option then a new class
        of network sockets are available for programming. The AX.25
        protocol is used primarily by Amateur Radio Operators for packet
        radio use.


  9.  Configuring the Network Devices.

  If everything has gone ok so far, then you will have a Linux kernel
  which supports the network devices you intend to use, and you also
  have the network tools with which to configure them. Now comes the fun
  part! You'll need to configure each of the devices you intend to use.
  This configuration generally amounts to telling each device things
  like what its IP address will be, and what network it is connected to.

  In past versions of this document I have presented near complete
  versions of the various configuration files and included comments to
  modify or delete lines from them as appropriate. From this version
  onwards I will take a slightly different approach which I hope will
  result in you having a complete set of uncluttered configuration files
  that you have built from scratch so you know exactly what is in them,
  and why. I'll describe each of these files, and their function, as we
  come to them.


  9.1.  Configuring the special device files in /dev

  You do not need to configure any special device files in the /dev
  directory for Linux Networking. Linux does not need or use them as
  other operating systems might. The devices are built dynamically in
  memory by the kernel, and since they are only names there is no need
  for them to have an appearance directly to you. The kernel provides
  all of the programming hooks and interfaces that you need to utilise
  them effectively.


  9.2.  What information do I need before I begin ?

  Before you can configure the networking software, you will need to
  know a number of pieces of information about your network connection.
  Your network provider or administrator will be able to provide you
  with most of them.





  9.2.1.  IP Address.

  This is the unique machine address, in dotted decimal notation, that
  your machine will use. An example is 128.253.153.54. Your network
  administrator will provide you with this information.

  If you will be using a slip or plip connection you may not need this
  information, so skip it until we get to the slip device.

  If you're using the loopback device only, ie no ethernet, slip or plip
  support, then you won't need an ip address as the loopback port always
  uses the address 127.0.0.1.


  9.2.2.  Network Mask (`netmask').

  For performance reasons it is desirable to limit the number of hosts
  on any particular segment of a network. For this reason it is common
  for network administrators to divide their network into a number of
  smaller networks, known as subnets, which each have a portion of the
  network addresses assigned to them. The network mask is a pattern of
  bits, which when overlayed onto an address on your network, will tell
  you which subnetwork it belongs to. This is very important for
  routing, and if you find for example, that you can happily talk to
  people outside your network, but not to some people on your own
  network, then it is quite likely that you have specified an incorrect
  subnet mask.

  Your network adminstrators will have chosen the netmask when the
  network was designed, and therefore they should be able to supply you
  with the correct mask to use. Most networks are class-C subnetworks
  which use 255.255.255.0 as their netmask. Other larger networks use
  class-B netmasks (255.255.0.0). The NET-2/NET-3 code will
  automatically select a default mask when you assign an address to a
  device. The default assumes that your network has not been subnetted.

  The NET-2/NET-3 code will choose the following masks by default:



       For addresses with the first byte:
       1-127         255.0.0.0         (Class A)
       128-191       255.255.0.0       (Class B)
       192+          255.255.255.0     (Class C)




  if one of these doesn't work for you, try another. If this doesn't
  work ask your network administrator or local network guru (dime a
  dozen) for help.

  You don't need to worry about a netmask for the loopback port, or if
  you are running slip/plip.


  9.2.3.  Network Address.

  This is your IP address masked (bitwise AND) with your netmask.  For
  example:






  If your netmask is:           255.255.255.0
  and your IP address is:       128.253.154.32    &&
                                            ---------------
  your Network address is:      128.253.154.0     =





  9.2.4.  Broadcast Address.

  `A shout is a whisper that everyone hears whether they need to or not'

  This is normally your network address logically ORed with your netmask
  inverted. This is simpler than it sounds. For a Class-C network, with
  network mask 255.255.255.0, your Broadcast Address will be your
  network address (calculated above), logically ORed with 0.0.0.255, the
  network mask inverted.

  A worked example might look like:


       If your netmask is:          255.255.255.0      !
       the netmask inverted is:       0.  0.  0.255    =
       If your Network address is:  128.253.154.0      ||
                                     ----------------
       Your broadcast address is:   128.253.154.255    =




  Note that for historical reasons some networks use the network address
  as the broadcast address. If you have any doubts contact your network
  administrator.

  If you have access to a sniffer, or some other device capable of
  providing you with a trace of your network traffic, then you might be
  able to determine both the network and broadcast addresses by watching
  other traffic on the lan. Keep an eye open for, (or filter everything
  except), ethernet frames destined for the ethernet broadcast address:
  ff:ff:ff:ff:ff:ff.  If any of them has an IP source address of your
  local router, and the protocol ID is not ARP, then check the
  destination IP address, because this datagram may well be a RIP
  routing broadcast from your router, in which case the destination IP
  address will be your broadcast address.

  Once again, if you're not sure, check with your network administrator,
  they'd rather help you, than have you connect your machine in a
  misconfigured way.


  9.2.5.  Router (`Gateway') Address.

  `There must be some way out of here.'

  This is the address of the machine that connects your network to the
  rest of the Internet. It is your `gateway' to the outside world. A
  couple of conventions exist for allocating addresses to routers which
  your network might follow, they are: The router is the lowest numbered
  address on the network, the router is the highest numbered host on the
  network.  Probably the most common is the first, where the router will
  have an address that is mostly the same as your own, except with a .1
  as the last byte. eg. if your address is 128.253.154.32, then your
  router might be 128.253.154.1. The router can in fact have any address
  valid on your network and function properly, the address doesn't
  matter at all. There may in fact even be more than one router on your
  network. You will probably need to talk to your network adminstrator
  to properly identify your router address.

  If you're using only loopback then you don't need a router address. If
  you're using PPP then you also don't need your router address, because
  PPP will automatically determine the correct address for you. If
  you're using SLIP, then your router address will be your SLIP server
  address.


  9.2.6.  Nameserver Address.

  Most machines on the net have access to a name server which translates
  human tolerable hostnames into machine tolerable addresses, and vice
  versa. Your network administrators will again tell you the address of
  your nearest nameserver. You can in fact run a nameserver on your own
  machine by running named, in which case your nameserver address will
  be 127.0.0.1, the loopback port address.  However it is not required
  that you run named at all; see section `named' for more information.

  If you're only using loopback then you don't need to know the
  nameserver address since you're only going to be talking to your own
  machine.


  9.2.7.  NOTE for SLIP/PLIP/PPP users.

  You may or may not in fact need to know any of the above information.
  Whether you do or not will depend on exactly how your network
  connection is achieved, and the capabilities of the machine at the
  other end of the link. You'll find more detail in the section relevant
  to configuration of the SLIP/PLIP and PPP devices.


  9.3.  /etc/rc.d/rc.inet1,2 or /etc/rc.net

  While the commands to configure your network devices can be typed
  manually each time, you will probably want to record them somewhere so
  that your network is configured automatically when you boot your
  machine.

  The `rc' files are specifically designed for this purpose. For the
  non-unix-wizard: `rc' file are run at bootup time by the init program
  and start up all of the basic system programs such as syslog, update,
  and cron. They are analagous to the MS-DOS autoexec.bat file, and rc
  might stand for `runtime commands'. By convention these files are kept
  under the /etc directory. The Linux Filesystem Standard doesn't go so
  far as to describe exactly where your rc files should go, stating that
  it is ok for them to follow either the BSD (/etc/rc.*) or System-V
  (/etc/rc.d/rc*) conventions.  Alan, Fred and I all use the System-V
  convention, so that is what you will see described here. This means
  that these files are found in /etc/rc.d and are called rc.inet1 and
  rc.inet2. The first rc file that gets called at bootup time is
  /etc/rc, and it in turn calls others, such as rc.inet1, which in turn
  might called rc.inet2.  It doesn't really matter where they are kept,
  or what they are called, so long as init can find them.

  In some distributions the rc file for the network is called rc.net and
  is in the /etc subdirectory. The rc.net file on these systems is
  simply the rc.inet1 and the rc.inet2 files combined into one file that
  gets executed. It doesn't matter where the commands appear, so long as
  you configure the interfaces before starting the network daemons and
  applications.

  I will refer to these files as rc.inet1 and rc.inet2, and I keep them
  in the /etc/rc.d, so if you are using one of the distributions that
  uses rc.net, or you want to keep the files somewhere else, then you
  will have to make appropriate adjustments as you go.

  We will be building these files from scratch as we go.


  9.3.1.  rc.inet1

  The rc.inet1 file configures the basic tcp/ip interaces for your
  machine using two programs: /sbin/ifconfig, and /sbin/route.


  9.3.1.1.  ifconfig

  /sbin/ifconfig is used for configuring your interfaces with the
  parameters that they require to function, such as their IP address,
  network mask, broadcast addresses and similar. You can use the
  ifconfig command with no parameters to display the configuration of
  all network devices. Please check the ifconfig man page for more
  detail on its use.


  9.3.1.2.  route

  /sbin/route is used to create, modify, and delete entries in a table
  (the routing table) that the networking code will look at when it has
  a datagram that it needs to transmit. The routing table lists
  destination address, and the interface that that address is reachable
  via. You can use the route command with no parameters to display the
  contents of the routing table. Please check the route man page for
  more detail on its use.



  9.3.2.  rc.inet2

  The rc.inet2 file starts any network daemons such as inetd, portmapper
  and so on. This will be covered in more detail in section `rc.inet2',
  so for the moment we will concentrate on rc.inet1. I have mentioned
  this file here so that if you have some other configuration, such as a
  single rc.net file you will understand what the second half of it
  represents. it is important to remember that you must start your
  network applications and daemons after you have configured your
  network devices.


  9.4.  Configuring the Loopback device (mandatory).

  The loopback device isn't really a hardware device. It is a software
  construct that looks like a physical interface. Its function is to
  happily allow you to connect to yourself, and to test network software
  without actually having to be connected to a network of any kind. This
  is great if you are developing network software and you have a slip
  connection.  You can write and test the code locally, and then when
  you are ready to test it on a live network, eatablish your slip
  connection and test it out. You won't hurt others users if your
  program misbehaves.

  By convention, the loopback device always has an IP address of
  127.0.0.1 and so you will use this address when configuring it.

  The loopback device for Linux is called `lo'. You will now make the
  first entry into your rc.inet1 file. The following code fragment will
  work for you:


       #!/bin/sh
       #
       # rc.inet1   --  configures network devices.
       #
       # Attach the loopback device.
       /sbin/ifconfig lo 127.0.0.1
       #
       # Add a route to point to the loopback device.
       /sbin/route add 127.0.0.1
       # End loopback
       #




  You have used the ifconfig program to give the loopback interface its
  IP address, and route program to create an entry in the routing table
  that will ensure that all datagrams destined for 127.0.0.1 will be
  sent to the loopback port.

  There are two important points to note here.

  Firstly, the netmask and broadcast addresses have been allowed to take
  the default values for the loopback device described earlier in
  section `Network Mask'. To see what they are, try the ifconfig program
  without any arguments.



       # ifconfig
       lo        Link encap Local Loopback
                 inet addr 127.0.0.1  Bcast 127.255.255.255  Mask 255.0.0.0
                 UP BROADCAST LOOPBACK RUNNING  MTU 2000  Metric 1
                 RX packets 0 errors 0 dropped 0 overrun 0
                 TX packets 30 errors 0 dropped 0 overrun 0
       #




  Secondly, its not obvious how the route command chose the loopback
  device as the device for the route to 127.0.0.1.  The route program is
  smart enough to know that 127.0.0.1 belongs to the network supported
  by the loopback device. It works this out by checking the IP address
  and the netmask. You can use the route command with no arguments to
  display the contents of the routing table:



       # route
       Kernel routing table
       Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
       127.0.0.0       *               255.0.0.0       U     0      0       30 lo
       #




  Note: You might want to use the -n argument if your name resolver is
  not yet configured properly. The -n argument tells route to just
  display the numeric addresses, and to not bother looking up the name.





  9.5.  Configuring an ethernet device. (optional)

  You'll only be interested in this section  if you wish to configure an
  ethernet card, if not then skip on ahead to the next section.

  To configure an ethernet card is only slightly more complicated than
  configuring the loopback device. This time you should probably specify
  explicitly the network mask and the broadcast address, unless you are
  sure that the defaults will work ok, and they probably will.

  For this you will need the IP address that you have been assigned, the
  network mask in use on your network, and the broadcast address in use.

  The first ethernet device for a Linux system is called `eth0', the
  second `eth1' and so forth. You will now add a section to your
  rc.inet1 file. The following code fragment will work for you if you
  change the addresses specified for real ones:



       #
       # Attach an ethernet device
       #
       #  configure the IP address, netmask and broadcast address.
       /sbin/ifconfig eth0 IPA.IPA.IPA.IPA
       /sbin/ifconfig eth0 netmask NMK.NMK.NMK.NMK
       /sbin/ifconfig eth0 broadcast BCA.BCA.BCA.BCA
       #
       # add a network route to point to it:
       /sbin/route add -net NWA.NWA.NWA.NWA device eth0
       #
       # End ethernet
       #




  Where:

     IPA.IPA.IPA.IPA
        represents your IP Address.

     NMK.NMK.NMK.NMK
        represents your netmask.

     BCA.BCA.BCA.BCA
        represents your Broadcast address.

     NWA.NWA.NWA.NWA
        represents your Network Address.

  Note the use of the -net argument to the route command.  This tells
  route that the route to be added is a route to a network, and not to a
  host. There is an alternative method of achieving this, you can leave
  off the -net if you have the network address listed in the
  /etc/networks file. This is covered later in section `/etc/networks'.


  9.6.  Configuring a SLIP device (optional)

  SLIP (Serial Line Internet Protocol) allows you to use tcp/ip over a
  serial line, be that a phone line with a dialup modem, or a leased
  line of some sort.  Of course to use slip you need access to a slip-
  server in your area. Many universities and businesses provide slip
  access all over the world.

  Slip uses the serial ports on your machine to carry IP datagrams. To
  do this it must take control of the serial device. Slip device names
  are named sl0, sl1 etc. How do these correspond to your serial devices
  ? The networking code uses what is called an ioctl (i/o control) call
  to change the serial devices into slip devices. There are two programs
  supplied that can do this, they are called dip and slattach


  9.6.1.  dip

  dip (Dialup IP) is a smart program that is able to set the speed of
  the serial device, command your modem to dial the remote end of the
  link, automatically log you into the remote server, search for
  messages sent to you by the server, and extract information for them
  such as your IP address, and perform the ioctl necessary to switch
  your serial port into slip mode. dip has a powerful scripting ability,
  and it is this that you can exploit to automate your logon procedure.

  dip used to be supplied with the net-tools, but since development of
  dip is now seperate, you have to source it seperately.  There have
  been a number of other versions of dip produced which offer a variety
  of new features. The dip-uri version seems to be the more popular, but
  I suggest you take a close look at each to determine which offers
  enhancements that you find useful. Since dip-uri is is so popular, the
  examples described in this document are based on current versions of
  it.

  You can find it at:

  sunsite.unc.edu


       /pub/Linux/system/Network/serial/dip337j-uri.tgz




  To install it, try the following:


       #
       # cd /usr/src
       # gzip -dc dip337j-uri.tgz | tar xvf -
       # cd dip.3.3.7j

       <edit Makefile>

       # make install
       #





  The Makefile assumes the existence of a group called uucp, but you
  might like to change this to either dip or slip depending on your
  configuration.


  9.6.2.  slattach

  slattach as contrasted with dip is a very simple program, that is very
  easy to use, but does not have the sophistication of dip.  It does not
  have the scripting ability, all it does is configure your serial
  device as a slip device. It assumes you have all the information you
  need and the serial line is established before you invoke it. slattach
  is ideal to use where you have a permanent connection to your server,
  such as a physical cable, or a leased line.


  9.6.3.  When do I use which ?

  You would use dip when your link to the machine that is your slip
  server is a dialup modem, or some other termporary link. You would use
  slattach when you have a leased line, perhaps a cable, between your
  machine and the server, and there is no special action needed to get
  the link working. See section `Permanent Slip connection' for more
  information.

  Configuring slip is much like configuring an Ethernet interface (read
  section `Configuring an ethernet device' above). However there are a
  few key differences.

  First of all, slip links are unlike ethernet networks in that there is
  only ever two hosts on the network, one at each end of the link.
  Unlike an ethernet that is available for use as soon are you are
  cabled, with slip, depending on the type of link you have, you may
  have to initialise your network connection in some special way.

  If you are using dip then this would not normally be done at boot
  time, but at some time later, when you were ready to use the link.  It
  is possible to automate this procedure. If you are using slattach then
  you will probably want to add a section to your rc.inet1 file.  This
  will be described soon.

  There are two major types of slip servers: Dynamic IP address servers
  and static IP address servers. Almost every slip server will prompt
  you to login using a username and password when dialing in. dip can
  handle logging you in automatically.


  9.6.4.  Static slip server with a dialup line and DIP.

  A static slip server in one in which you have been supplied an IP
  address that is exclusively yours. Each time you connect to the
  server, you will configure your slip port with that address. The
  static slip server will answer your modem call, possibly prompt you
  for a username and password, and then route any datagrams destined for
  your address to you via that connection. If you have a static server,
  then you may want to put entries for your hostname and IP address
  (since you know what it will be) into your /etc/hosts. You should also
  configure some other files such as: rc.inet2, host.conf, resolv.conf,
  /etc/HOSTNAME, and rc.local. Remember that when configuring rc.inet1,
  you don't need to add any special commands for your slip connection
  since it is dip that does all of the hard work for you in configuring
  your interface. You will need to give dip the appropriate information,
  and it will configure the interface for you after commanding the modem
  to establish the call, and logging you into your slip server.

  If this is how your slip server works then you can move to section
  `Using Dip' to learn how to configure dip appropriately.


  9.6.5.  Dynamic slip server with a dialup line and DIP.

  A dynamic slip server is one which allocates you an IP address
  randomly, from a pool of addresses, each time you logon. This means
  that there is no guarantee that you will have any particular address
  each time, and that address may well be used by someone else after you
  have logged off.  The netework administrator who configured the slip
  server will have assigned a pool of address for the slip server to
  use, when the server receives a new incoming call, it finds the first
  unused address, guides the caller through the login process, and then
  prints a welcome message that contains the IP address it has
  allocated, and will proceed to use that IP address for the duration of
  that call.

  Configuring for this type of server is similar to configuring for a
  static server, except that you must add a step where you obtain the IP
  address that the server has allocated for you and configure your slip
  device with that.

  Again, dip does the hard work, and new versions are smart enough to
  not only log you in, but to also be able to automatically read the IP
  address printed in the welcome message, and store it so that you can
  have it configure your slip device with it.

  If this is how your slip server works then you can move to section
  `Using Dip' to learn how to configure dip appropriately.


  9.6.6.  Using DIP.

  As explained earlier, dip is a powerful program that can simplify and
  automate the process of dialling into the slip server, logging you in,
  starting the connection, and configuring your slip devices with the
  appropriate ifconfig and route commands.

  Essentially to use dip you'll write a `dip script', which is basically
  a list of commands that dip understands that tell dip how to perform
  each of the actions you want it to perform. See sample.dip that comes
  supplied with dip to get an idea of how it works. dip is quite a
  powerful program, with many options.  Instead of going into all of
  them here you should looks at the man page, README and sample files
  that will have come with your version of dip.

  You may notice that the sample.dip script assumes that you're using a
  static slip server, so you know what your IP address is beforehand.
  For dynamic slip servers, the newer versions of dip include a command
  you can use to automatically read and configure your slip device with
  the IP address that the dynamic server allocates for you. The
  following sample is a modified verson of the sample.dip that came
  supplied with dip337j-uri.tgz, and is probably a good starting point
  for you.  You might like to save it as /etc/dipscript and edit it to
  suit your configuration:























  #
  # sample.dip    Dialup IP connection support program.
  #
  #               This file (should show) shows how to use the DIP
  #       This file should work for Annex type dynamic servers, if you
  #       use a static address server then use the sample.dip file that
  #       comes as part of the dip337-uri.tgz package.
  #
  #
  # Version:      @(#)sample.dip  1.40    07/20/93
  #
  # Author:       Fred N. van Kempen, <[e-mail]>
  #

  main:
  # Next, set up the other side's name and address.
  # My dialin machine is called 'xs4all.hacktic.nl' (== 193.78.33.42)
  get $remote xs4all.hacktic.nl
  # Set netmask on sl0 to 255.255.255.0
  netmask 255.255.255.0
  # Set the desired serial port and speed.
  port cua02
  speed 38400

  # Reset the modem and terminal line.
  # This seems to cause trouble for some people!
  reset

  # Note! "Standard" pre-defined "errlevel" values:
  #  0 - OK
  #  1 - CONNECT
  #  2 - ERROR
  #
  # You can change those grep'ping for "addchat()" in *.c...

  # Prepare for dialing.
  send ATQ0V1E1X4\r
  wait OK 2
  if $errlvl != 0 goto modem_trouble
  dial 555-1234567
  if $errlvl != 1 goto modem_trouble

  # We are connected.  Login to the system.
  login:
  sleep 2
  wait ogin: 20
  if $errlvl != 0 goto login_trouble
  send MYLOGIN\n
  wait ord: 20
  if $errlvl != 0 goto password_error
  send MYPASSWD\n
  loggedin:

  # We are now logged in.
  wait SOMEPROMPT 30
  if $errlvl != 0 goto prompt_error

  # Command the server into SLIP mode
  send slip\n
  wait SLIP 30
  if $errlvl != 0 goto prompt_error

  # Get and Set your IP address from the server.
  #   Here we assume that after commanding the slip server into SLIP
  #   mode that it prints your IP address
  get $locip remote 30
  if $errlvl != 0 goto prompt_error

  # Set up the SLIP operating parameters.
  get $mtu 296
  # Ensure "route add -net default xs4all.hacktic.nl" will be done
  default

  # Say hello and fire up!
  done:
  print CONNECTED $locip ---> $rmtip
  mode CSLIP
  goto exit

  prompt_error:
  print TIME-OUT waiting for SLIPlogin to fire up...
  goto error

  login_trouble:
  print Trouble waiting for the Login: prompt...
  goto error

  password:error:
  print Trouble waiting for the Password: prompt...
  goto error

  modem_trouble:
  print Trouble ocurred with the modem...
  error:
  print CONNECT FAILED to $remote
  quit

  exit:
  exit




  The above example assumes you are calling a dynamic slip server, if
  you are calling a static slip server, then the sample.dip file that
  comes with dip337j-uri.tgz should work for you.

  When dip is given the get $local command it searches the incoming text
  from the remote end for a string that looks like an IP address, ie
  strings numbers seperated by `.' characters. This modification was put
  in place specifically for dynamic slip servers, so that the process of
  reading the IP address granted by the server could be automated.

  The example above will automaticaly create a default route via your
  slip link, if this is not what you want, you might have an ethernet
  connection that should be your default route, then remove the default
  command from the script.  After this script has finished running, if
  you do an ifconfig command, you will see that you have a device sl0.
  This is your slip device.  Should you need to, you can modify its
  configuration manually, after the dip command has finished, using the
  ifconfig and route commands.

  Please note that dip allows you to select a number of different
  protocols to use with the mode command, the most common example is
  cslip for slip with compression. Please note that both ends of the
  link must agree, so you should ensure that whatever you select agrees
  with what your server is set to.

  The above example is fairly robust and should cope with most errors.
  Please refer to the dip man page for more information. Naturally you
  could, for example, code the script to do such things as redial the
  server if it doesn't get a connection within a prescribed period of
  time, or even try a series of servers if you have access to more than
  one.


  9.6.7.  Permament slip connection using a leased line and slattach.

  If you have a cable between two machines, or are fortunate enough to
  have a leased line, or some other permanent serial connection between
  your machine and another, then you don't need to go to all the trouble
  of using dip to set up your serial link. slattach is a very simple to
  use utility that will allow you just enough functionality to configure
  your connection.

  Since your connection will be a permanent one, you will want to add
  some commands to your rc.inet1 file. In essence all you need to do for
  a permament connection is ensure that you configure the serial device
  to the correct speed and switch the serial device into slip mode.
  slattach allows you to do this with one command. Add the following to
  your rc.inet1 file:



       #
       # Attach a leased line static slip connection
       #
       #  configure /dev/cua0 for 19.2kbps and cslip
       /sbin/slattach -p cslip -s 19200 /dev/cua0 &
       /sbin/ifconfig sl0 IPA.IPA.IPA.IPA pointopoint IPR.IPR.IPR.IPR up
       #
       # End static slip.




  Where:

     IPA.IPA.IPA.IPA
        represents your IP address.

     IPR.IPR.IPR.IPR
        represents the IP address of the remote end.

  slattach allocated the first unallocated slip device to the serial
  device specified. slattach starts with sl0. Therefore the first
  slattach command attaches slip device sl0 to the serial device
  specified, and sl1 the next time, etc.

  slattach allows you to configure a number of different protocols with
  the -p argument. In your case you will use either slip or cslip
  depending on whether you want to use compression or not.  Note: both
  ends must agree on whether you want compression or not.


  9.7.  Configuring a PLIP device. (optional)

  plip (Parallel Line IP), is like slip, in that it is used for
  providing a point to point network connection between two machines,
  except that it is designed to use the parallel printer ports on your
  machine instead of the serial ports. Because it is possible to
  transfer more than one bit at a time with a parallel port, it is
  possible to attain higher speeds with the plip interface than with a
  standard serial device. In addition, even the simplest of parallel
  ports, printer ports, can be used, in lieu of you having to purchase
  comparitively expensive 16550AFN UART's for your serial ports.


  Please note that some laptops use chipsets that will not work with
  PLIP because they do not allow some combinations of signals that PLIP
  relies on, that printers don't use.

  The Linux plip interface is compatible with the Crywyr Packet Driver
  PLIP, and this will mean that you can connect your Linux machine to a
  DOS machine running any other sort of tcp/ip software via plip.

  You have two options in using the PLIP driver. You can either compile
  the driver into your kernel, or use the modules package to load the
  module dynamically. I recommend just compiling it into your kernel as
  it is probably the easiest, and in most circumstances you will want
  the driver there all the time anyway.

  When compiling the kernel, there is only one file that might need to
  be looked at to configure plip. That file is
  /usr/src/linux/driver/net/CONFIG, and it contains plip timers in mS.
  The defaults are probably ok in most cases. You will probably need to
  increase them if you have an especially slow computer, in which case
  the timers to increase are actually on the other computer.

  The driver assumes the following defaults:


       device  i/o addr    IRQ
       ------  --------    -----
       plip0   0x3BC           5
       plip1   0x378           7
       plip2   0x278           2 (9)




  If your parallel ports don't match any of the above combinations then
  you can change the IRQ of a port using the ifconfig command using the
  `irq' paramater. Be sure to enable IRQ's on your printer ports in your
  ROM BIOS if it supports this option.

  To configure a plip interface, you will need to add the following
  lines to your rc.inet1 file:



       #
       # Attach a PLIP interface
       #
       #  configure first parallel port as a plip device
       /sbin/ifconfig plip0 IPA.IPA.IPA.IPA pointopoint IPR.IPR.IPR.IPR up
       #
       # End plip




  Where:

     IPA.IPA.IPA.IPA
        represents your IP address.

     IPR.IPR.IPR.IPR
        represents the IP address of the remote machine.

  The pointopoint parameter has the same meaning as for slip, in that it
  specifies the address of the machine at the other end of the link.


  In almost all respects you can treat a plip interface as though it
  were a slip interface, except that neither dip nor slattach need be,
  nor can be, used.


  9.7.1.  PLIP cabling diagram.

  plip has been designed to use cables with the same pinout as those
  commonly used by the better known of the MS-DOS based pc-pc file
  transfer programs.


  The pinout diagram (taken from /usr/src/linux/drivers/net/plip.c)
  looks as follows:



       Pin Name    Connect pin - pin
       ---------   -------------------------------
       GROUND      25 - 25
       D0->ERROR   2 - 15
       ERROR->D0   15 - 2
       D1->SLCT    3 - 13
       SLCT->D1    13 - 3
       D2->PAPOUT  4 - 12
       PAPOUT->D2  12 - 4
       D3->ACK     5 - 10
       ACK->D3     10 - 5
       D4->BUSY    6 - 11
       BUSY->D4    11 - 6
       D5          7*
       D6          8*
       D7          9*
       STROBE      1*
       FEED        14*
       INIT        16*
       SLCTIN      17*




  Notes: Do not connect the pins marked with an asterisk `*'.  Extra
  grounds are 18,19,20,21,22,23, and 24.

  If the cable you are using has a metallic shield, it should be
  connected to the metallic DB-25 shell at one end only.

  Warning: A miswired PLIP cable can destroy your controller card. Be
  very careful, and double check every connection to ensure you don't
  cause yourself any unnecessary work or heartache.

  While you may be able to run PLIP cables for long distances, you
  should avoid it if you can. The specifications for the cable allow for
  a cable length of about 1 metre or so. Please be very careful when
  running long plip cables as sources of strong electromagnetic fields
  such as lightning, power lines, and radio transmitters can interfere
  with and sometimes even damage your controller. If you really want to
  connect two of your computers over a large distance you really should
  be looking at obtaining a pair of thin-net ethernet cards and running
  some coaxial cable.


  10.  Routing. (mandatory)

  After you have configured all of your network devices you need to
  think about how your machine is going to route IP datagrams. If you
  have only one network device configured then your choice is easy, as
  all datagrams for any machine other than yours must go via that
  interface. If you have more than one network interface then your
  choice is a little more complicated. You might have both an ethernet
  device and slip connection to your machine at home. In this situation
  you must direct all datagrams for your machine at home via your slip
  interface, and all else via the ethernet device. Routing is actually a
  very simple mechanism, but don't worry if you find it slightly
  difficult to understand at first; everybody does.

  You can display the contents of your routing table by using the route
  command without any options.

  There are four commonly used routing mechanisms for unix network
  configurations.  I'll briefly discuss each in turn.


  10.1.  Static/Manual Routes.

  Static routing, as its name implies, is `hard coded' routing, that is,
  it will not change if your network suffers some failure, or if an
  alternate route becomes available. Static routes are often used in
  cases where you have a very simple network with no alternate routes
  available to a destination host, that is, there is only one possible
  network path to a destination host, or where you want to route a
  particular way to a host regardless of network changes.

  In Linux there is a special use for manual routes, and that is for
  adding a route to a slip or plip host where you have used the ifconfig
  pointopoint parameter. If you have a slip/plip link, and have the
  pointopoint parameter specifying the address of the remote host, then
  you should add a static route to that address so that the ip routing
  software knows how to route datagrams to that address. The route
  command you would use for the slip/plip link via leased line example
  presented earlier would be:



       #/sbin/route add IPR.IPR.IPR.IPR




  Where:

     IPR.IPR.IPR.IPR
        represents the IP address of the remote end.


  10.2.  Default Route.

  The default route mechanism is probably the most common and most
  useful to most end-user workstations and hosts on most networks. The
  default route is a special static route that matches every destination
  address, so that if there is no more specific route for a datagram to
  be sent to, then the default route will be used.

  If you have a configuration where you have only a single ethernet
  interface, or a single slip interface device defined then you should
  point your default route via it. In the case of an ethernet interface,
  the Linux kernel knows where to send datagrams for any host on your
  network. It works this out using the network address and the network
  mask as discussed earlier. This means that the only datagrams the
  kernel won't know how to properly route will be those for people not
  on your network. To make this work you would normally have your
  default route point to your router address, as it is your means of
  getting outside of your local network. If you are using a slip
  connection, then your slip server will be acting as your router, so
  your default route will be via your slip server.

  To configure your default route, add the following to your rc.inet1
  after all of your network device configurations:



       #
       # Add a default route.
       #
       /sbin/route add default gw RGA.RGA.RGA.RGA
       #




  Where:

     RGA.RGA.RGA.RGA
        represents your Router/Gateway Address.


  10.3.  Proxy ARP.

  This method is ugly, hazard prone and should be used with extreme
  care, some of you will want to use it anyway.

  Those with the greatest need for proxy arp will be those of you who
  are configuring your Linux machine as a slip dial-in server. For those
  of you who will be using PPP, the PPP daemon simplifies and automates
  this task, making it a lot safer to use.

  Normally when a tcp/ip host on your ethernet network wants to talk to
  you, it knows your IP address, but doesn't know what hardware
  (ethernet) address to send datagrams to. The ARP mechanism is there
  specifically to provide that mapping function between network address
  and hardware address. The ethernet protocol provides a special address
  that is recognised by all ethernet cards, this is called the broadcast
  address. ARP works by sending a specially formatted datagram
  containing the IP address of the host it wishes to discover the
  hardware address of, and transmits it to the ethernet broadcast
  address.  Every host will receive this datagram and the host that is
  configured with the matching IP address will reply with its hardware
  address. The host that performed the arp will then know what hardware
  address to use for the desired IP address.

  If you want to use your machine as a server for other machines, you
  must get your machine to answer ARP requests for their IP addresses on
  their behalf, as they will not be physically connected to the ethernet
  network. Lets say that you have been assigned a number of IP addresses
  on your local network that you will be offering to dial-in slip users.
  Lets say those addresses are: 128.253.154.120-124, and that you have
  an ethernet card with a hardware address of 00:00:C0:AD:37:1C. (You
  can find the hardware address of your ethernet card by using the
  ifconfig command with no options). To instruct your Linux server to
  answer arp requests by proxy for these addresses you would need to add
  the following commands to the end of your rc.inet1 file:







  #
  # Proxy ARP for those dialin users who will be using this
  #           machine as a server:
  #
  /sbin/arp -s 128.263.154.120 00:00:C0:AD:37:1C pub
  /sbin/arp -s 128.263.154.121 00:00:C0:AD:37:1C pub
  /sbin/arp -s 128.263.154.122 00:00:C0:AD:37:1C pub
  /sbin/arp -s 128.263.154.123 00:00:C0:AD:37:1C pub
  /sbin/arp -s 128.263.154.124 00:00:C0:AD:37:1C pub
  #
  # End proxy arps.




  The pub argument stands for `publish'. It is this argument that
  instructs your machine to answer requests for these addresses, even
  though they are not for your machine. When it answers it will supply
  the hardware address specified, which is of course its own hardware
  address.

  Naturally you will need to ensure that you have routes configured in
  your linux server that point these addresses to the slip device on
  which they will be connecting.

  If you are using PPP, you don't need to worry about manually messing
  with the arp table, as the pppd will manage those entries for you if
  you use the proxyarp parameter, and as long as the IP addresses of the
  remote machine and the server machine are in the same network. You
  will need to supply the netmask of the network on the server's pppd
  command line.


  10.4.  gated - the routing daemon.

  gated could be used in place of proxy arp in some cases, and would
  certainly be much cleaner, but its primary use is if you want your
  linux machine to act as an intelligent ip router for your network.
  gated provides support for a number of routing protocols. Among these
  are RIP, BGP, EGP, HELLO, and OSPF. The most commonly used in small
  networks being rip. rip stands for `Routing Information Protocol'. If
  you run gated, configured for rip, your linux machine will
  periodically broadcast a copy of its routing table to your network in
  a special format. In this way, all of the other machines on your
  network will know what addresses are accessible via your machine.

  gated can be used to replace proxy arp when all hosts on your network
  run either gated or routed. If you have a network where you use a
  mixture of manual and dynamic routes, you should mark any manual
  routes as passive to ensure that they aren't destroyed by gated
  because it hasn't received an update for them. The best way to add
  static routes if you are using gated is to add a static stanza to your
  /etc/gated.conf file. This is described below.

  gated would normally be started from your rc.inet2 which is covered in
  the next section. You might already see a daemon called routed
  running. gated is superior to routed in that it is more flexible and
  more functional. So you should use gated and not routed.


  10.4.1.  Obtaining gated

  Gated is available from:

  sunsite.unc.edu

  /pub/Linux/system/Network/daemons/gated11_bin.tgz





  10.4.2.  Installing gated

  The gated binary distribution comprises three programs and two sample
  configuration files.

  The programs are:


     gated
        the actual gated daemon.

     gdc
        the operational user interface for gated. gdc is for controlling
        the gated daemon, stopping and starting it, obtaining its status
        and the like.

     ripquery
        a diagnostic tool to query the known routes of a gateway using
        either a `rip query' or a `rip poll'.

  The configuration files are:


     gated.conf
        this is the actual configuration file for the gated daemon. It
        allows you to specify how gated will behave when it is running.
        You can enable and disable any of the routing protocols, and
        control the behaviour of those routing protocols running.

     gated.version
        a text file that describes the version number of the gated
        daemon

  The gated binary distribution will not install the gated files in the
  correct place for you. Fortunately there aren't very many, so its
  fairly simple to do.

  To install the binaries try the following:



       # cd /tmp
       # gzip -dc .../gated.linux.bin.tgz | tar xvf -
       # install -m 500 bin/gated /usr/sbin
       # install -m 444 bin/gated.conf bin/gated.version /etc
       # install -m 555 bin/ripquery bin/gdc /sbin
       # rm -rf /tmp/bin




  I keep the networking daemons in /usr/sbin, if yours are somewhere
  else then naturally you'll have to change the target directory. The
  sample gated configuration file included configures gated to emulate
  the old routed daemon. It will probably work for you in most
  circumstances, and it looks like this:




  #
  #  This configuration emulates routed.  It runs RIP and only sends
  #  updates if there are more than one interfaces up and IP forwarding is
  #  enabled in the kernel.
  #
  #       NOTE that RIP *will not* run if UDP checksums are disabled in
  #       the kernel.
  #
  rip yes ;
  traceoptions all;
  #




  If you have any static routes you wish to add, you can add them in a
  static stanza appended to your /etc/gated.conf as follows:



       #
       static {
       37.0.0.0 mask 255.0.0.0 gateway 44.136.8.97 ;
       host 44.136.8.100 gateway 44.136.8.97 ;
       } ;
       #




  The above example would create a static route to the Class A network
  37.0.0.0 via gateway 44.136.8.97, and a static route to a host with
  address 44.136.8.100 via gateway 44.136.8.97.  If you do this you do
  not need to add the routes using the route command, gated will add and
  manage the routes for you.


  To install the man files, try the following:



       # cd /tmp
       # gzip -dc .../gated.linux.man.tgz | tar xvf -
       # install -m 444 man/*.8 /usr/man/man8
       # install -m 444 man/*.5 /usr/man/man5
       # rm -rf /tmp/man




  The man files contain concise and detailed information on the
  configuration and use of gated. For information on configuring gated,
  refer to the gated-config man page.


  11.  Configuring the network daemons.

  As mentioned earlier, there are other files that you will need to
  complete your network installation. These files concern higher level
  configurations of the network software. Each of the important ones are
  covered in the following sub-sections, but you will find there are
  others that you will have to configure as you become more familiar
  with the network suite.



  11.1.  /etc/rc.d/rc.inet2 (the second half of rc.net)

  If you have been following this document you should at this stage have
  built an rc file to configure each of your network devices with the
  correct addresses, and set up whatever routing you will need for your
  particular network configuration. You will now need to actually start
  some of the higher level network software.

  Now would be a really good time to read Olaf's Network Administrators
  Guide, as it really should be considered the definitive document for
  this stage of the configuration process. It will help you decide what
  to include in this file, and more importantly perhaps, what not to
  include in this file. For the security conscious it is a fair
  statement to say that the more network services you have running, the
  more likely the chance of your system having a security hole: Run only
  what you need.

  There are some very important daemons (system processes that run in
  the background) that you will need to know a little about. The man
  pages will tell you more, but they are:


  11.1.1.  inetd.

  inetd is a program that sits in the background and manages internet
  connection requests and the like. It is smart enough that you don't
  need to leave a whole bunch of servers running when there is nothing
  connected to them.  When it sees an incoming request for a particular
  service, eg telnet, or ftp, it will check the /etc/services file, find
  what server program needs to be run to manage the request, start it,
  and hand the connection over to it. Imagine it as a master server for
  your internet servers. It also has a few simple standard services
  inbuilt. These are echo, discard and generate services used for
  various types of network testing. inetd doesn't manage all servers and
  services that you might run, but it manages most of the usual ones.
  Normally services such as udp based services, or services that manage
  their own connection multiplexing such as World Wide Web servers or
  muds would be run independently of inetd. Generally the documentation
  accompanying such servers will tell you whether to use inetd or not.


  11.1.2.  syslogd.

  syslogd is a daemon that handles all system logging. It accepts
  messages generated for it and will distribute them according to a set
  of rules contained in /etc/syslogd.conf. For example, certain types of
  messages you will want to send to the console, and also to a log file,
  where others you will want only to log to a file. syslogd allows you
  to specify what messages should go where.


  11.2.  A sample rc.inet2 file.

  The following is a sample rc.inet2 file that Fred built. It starts a
  large number of servers, so you might want to trim it down to just
  those services that you actually want to run. To trim it down, simply
  delete or comment out the stanzas (if to fi) that you don't need. All
  each stanza does is test that the relevant module is a file, that it
  exists, echoes a comment that you can see when you boot your machine,
  and then executes the commands with the arguments supplied to ensure
  that it runs happily in the background. For more detailed information
  on each of the deamons, check either the Network Administrators Guide
  or the relevant man pages.



  #! /bin/sh
  #
  # rc.inet2      This shell script boots up the entire INET system.
  #               Note, that when this script is used to also fire
  #               up any important remote NFS disks (like the /usr
  #               distribution), care must be taken to actually
  #               have all the needed binaries online _now_ ...
  #
  # Version:      @(#)/etc/rc.d/rc.inet2  2.18    05/27/93
  #
  # Author:       Fred N. van Kempen, <[e-mail]>
  #

  # Constants.
  NET="/usr/sbin"
  IN_SERV="lpd"
  LPSPOOL="/var/spool/lpd"

  # At this point, we are ready to talk to The World...
  echo -e "\nMounting remote file systems ..."
  /bin/mount -t nfs -v            # This may be our /usr runtime!!!

  echo -e "\nStarting Network daemons ..."
  # Start the SYSLOG daemon.  This has to be the first server.
  # This is a MUST HAVE, so leave it in.
  echo -n "INET: "
  if [ -f ${NET}/syslogd ]
  then
  echo -n "syslogd "
  ${NET}/syslogd
  fi

  # Start the SUN RPC Portmapper.
  if [ -f ${NET}/rpc.portmap ]
  then
  echo -n "portmap "
  ${NET}/rpc.portmap
  fi

  # Start the INET SuperServer
  # This is a MUST HAVE, so leave it in.
  if [ -f ${NET}/inetd ]
  then
  echo -n "inetd "
  ${NET}/inetd
  else
  echo "no INETD found.  INET cancelled!"
  exit 1
  fi

  # Start the NAMED/BIND name server.
  # NOTE: you probably don't need to run named.
  #if [ ! -f ${NET}/named ]
  #then
  #        echo -n "named "
  #        ${NET}/named
  #fi

  # Start the ROUTEd server.
  # NOTE: routed is now obselete. You should now use gated.
  #if [ -f ${NET}/routed ]
  #then
  #        echo -n "routed "
  #        ${NET}/routed -q #-g -s
  #fi

  # Start the GATEd server.
  if [ -f ${NET}/gated ]
  then
  echo -n "gated "
  ${NET}/gated
  fi

  # Start the RWHO server.
  if [ -f ${NET}/rwhod ]
  then
  echo -n "rwhod "
  ${NET}/rwhod -t -s
  fi

  # Start the U-MAIL SMTP server.
  if [ -f XXX/usr/lib/umail/umail ]
  then
  echo -n "umail "
  /usr/lib/umail/umail -d7 -bd </dev/null >/dev/null 2>&1 &
  fi

  # Start the various INET servers.
  for server in ${IN_SERV}
  do
  if [ -f ${NET}/${server} ]
  then
                  echo -n "${server} "
                  ${NET}/${server}
  fi
  done

  # Start the various SUN RPC servers.
  if [ -f ${NET}/rpc.portmap ]
  then
  if [ -f ${NET}/rpc.ugidd ]
  then
                  echo -n "ugidd "
                  ${NET}/rpc.ugidd -d
  fi
  if [ -f ${NET}/rpc.mountd ]
  then
                  echo -n "mountd "
                  ${NET}/rpc.mountd
  fi
  if [ -f ${NET}/rpc.nfsd ]
  then
                  echo -n "nfsd "
                  ${NET}/rpc.nfsd
  fi

  # Fire up the PC-NFS daemon(s).
  if [ -f ${NET}/rpc.pcnfsd ]
  then
                  echo -n "pcnfsd "
                  ${NET}/rpc.pcnfsd ${LPSPOOL}
  fi
  if [ -f ${NET}/rpc.bwnfsd ]
  then
                  echo -n "bwnfsd "
                  ${NET}/rpc.bwnfsd ${LPSPOOL}
  fi

  fi
  echo network daemons started.
  # Done!

  11.3.  Other necessary network configuration files.

  There are other network configuraiton files that you will need to
  configure if you want to have people connect to and use your machine
  as a host. If you have installed your linux from a distribution then
  you will probably already have copies of these files so just check
  them to make sure they look ok, and if not you can use the following
  samples.


  11.3.1.  A sample /etc/inetd.conf file.

  Your /etc/rc.d/rc.inet2 file will have started inetd, syslogd and the
  various rpc servers for you. You will now need to configure the
  network daemons that will be managed by inetd. inetd uses a
  configuration file called /etc/inetd.conf.

  The following is an example of how a simple configuration might look:



       #
       # The internal services.
       #
       # Authors:      Original taken from BSD UNIX 4.3/TAHOE.
       #               Fred N. van Kempen, <[e-mail]>
       #
       echo    stream tcp nowait root  internal
       echo    dgram  udp wait   root  internal
       discard stream tcp nowait root  internal
       discard dgram  udp wait   root  internal
       daytime stream tcp nowait root  internal
       daytime dgram  udp wait   root  internal
       chargen stream tcp nowait root  internal
       chargen dgram  udp wait   root  internal
       #
       # Standard services.
       #
       ftp     stream tcp nowait root  /usr/sbin/tcpd in.ftpd ftpd
       telnet  stream tcp nowait root  /usr/sbin/tcpd in.telnetd
       #
       # Shell, login, exec and talk are BSD protocols.
       #
       shell   stream tcp nowait root  /usr/sbin/tcpd in.rshd
       login   stream tcp nowait root  /usr/sbin/tcpd in.rlogind
       exec    stream tcp nowait root  /usr/sbin/tcpd in.rexecd
       talk    dgram  udp wait   root  /usr/sbin/tcpd in.talkd
       ntalk   dgram  udp wait   root  /usr/sbin/tcpd in.talkd
       #
       # Status and Information services.
       #
       finger  stream tcp nowait root  /usr/sbin/tcpd in.fingerd
       systat  stream tcp nowait guest /usr/sbin/tcpd /usr/bin/ps -auwwx
       netstat stream tcp nowait guest /usr/sbin/tcpd /bin/netstat
       #
       # End of inetd.conf.




  The inetd man page describes what each of the fields are, but put
  simply, each entry describes what program should be executed when an
  incoming connection is received on the socket listed as the first
  entry. Those entries which have incoming where the program name and
  arguments would be are those services that are provided internally by
  the inetd program.
  The conversion between the service name in the first column, and the
  actual socket number it refers to is performed by the /etc/services
  file.


  11.3.2.  A sample /etc/services file.

  The /etc/services file is a simple table of Internet service names and
  the socket number and protocol is uses. This table is used by a number
  of programs including inetd, telnet and tcpdump.  It makes life a
  little easier by allowing us to refer to services by name rather than
  by number.

  The following is a sample of what a simple /etc/services file might
  look like:



















































  #
  # /etc/services - database of service name, socket number
  #                 and protocol.
  #
  # Original Author:
  #     Fred N. van Kempen, <[e-mail]>
  #
  tcpmux     1/tcp
  echo       7/tcp
  echo       7/udp
  discard    9/tcp   sink null
  discard    9/udp   sink null
  systat     11/tcp  users
  daytime    13/tcp
  daytime    13/udp
  netstat    15/tcp
  chargen    19/tcp  ttytst source
  chargen    19/udp  ttytst source
  ftp-data   20/tcp
  ftp        21/tcp
  telnet     23/tcp
  smtp       25/tcp  mail
  time       37/tcp  timserver
  time       37/udp  timserver
  name       42/udp  nameserver
  whois      43/tcp  nicname    # usually to sri-nic
  domain     53/tcp
  domain     53/udp
  finger     79/tcp
  link       87/tcp  ttylink
  hostnames  101/tcp hostname   # usually to sri-nic
  sunrpc     111/tcp
  sunrpc     111/tcp portmapper # RPC 4.0 portmapper TCP
  sunrpc     111/udp
  sunrpc     111/udp portmapper # RPC 4.0 portmapper UDP
  auth       113/tcp authentication
  nntp       119/tcp usenet     # Network News Transfer
  ntp        123/tcp            # Network Time Protocol
  ntp        123/udp            # Network Time Protocol
  snmp       161/udp
  snmp-trap  162/udp
  exec       512/tcp            # BSD rexecd(8)
  biff       512/udp comsat
  login      513/tcp            # BSD rlogind(8)
  who        513/udp whod       # BSD rwhod(8)
  shell      514/tcp cmd        # BSD rshd(8)
  syslog     514/udp            # BSD syslogd(8)
  printer    515/tcp spooler    # BSD lpd(8)
  talk       517/udp            # BSD talkd(8)
  ntalk      518/udp            # SunOS talkd(8)
  route      520/udp routed     # 521/udp too
  timed      525/udp timeserver
  mount      635/udp            # NFS Mount Service
  pcnfs      640/udp            # PC-NFS DOS Authentication
  bwnfs      650/udp            # BW-NFS DOS Authentication
  listen     1025/tcp listener  # RFS remote_file_sharing
  ingreslock 1524/tcp           # ingres lock server
  nfs        2049/udp           # NFS File Service
  irc        6667/tcp           # Internet Relay Chat
  # End of services.




  The telnet entry tells us that the telnet service uses socket number
  23 and the tcp protocol. The domain entry tells us that the Domain
  Name Service uses socket number 52 and both tcp and udp protocols. You
  should have an appropriate /etc/services entry for each
  /etc/inetd.conf entry.


  11.3.3.  A sample /etc/protocols file.

  The /etc/protocols file is a table of protocol name with its
  corresponding protocol number. Since the number of protocols in use is
  small this file is quite trivial.



       #
       # /etc/protocols - database of protocols.
       #
       # Original Author:
       #   Fred N. van Kempen, <[e-mail]>
       #
       ip   0   IP   # internet protocol
       icmp 1   ICMP # internet control message protocol
       igmp 2   IGMP # internet group multicast protocol
       ggp  3   GGP  # gateway-gateway protocol
       tcp  6   TCP  # transmission control protocol
       pup  12  PUP  # PARC universal packet protocol
       udp  17  UDP  # user datagram protocol
       idp  22  IDP
       raw  255 RAW
       #
       # End of protocols.





  11.4.  Name Resolution.

  Name Resolution is the process of converting a hostname in the
  familiar dotted notation (e.g. tsx-11.mit.edu) into an IP address
  which the network software understands. There are two principal means
  of achieving this in a typical installation, one simple, and one more
  complex.


  11.4.1.  /etc/hosts

  /etc/hosts contains a list of ip addresses and the hostnames they map
  to. In this way, you can refer to other machines on the network by
  name, as well as their ip address. Using a nameserver (see section
  `named') allows you to do the same name->ip address translation
  automatically. (Running named allows you to run your own nameserver on
  your linux machine).  This file needs to contain at least an entry for
  127.0.0.1 with the name localhost. If you're not only using loopback,
  you need to add an entry for your ip address, with your full hostname
  (such as loomer.vpizza.com). You may also wish to include entries for
  your gateways and network addresses.

  For example, if loomer.vpizza.com has the ip address 128.253.154.32,
  the /etc/hosts file would contain:







  # /etc/hosts
  # List of hostnames and their ip addresses
  127.0.0.1               localhost
  128.253.154.32          loomer.vpizza.com loomer
  # end of hosts




  Once again you will need to edit this file to suit your own needs. If
  you're only using loopback, the only line in /etc/hosts should be for
  127.0.0.1, with both localhost and your hostname after it.

  Note that in the second line, above, there are two names for
  128.253.154.32: loomer.vpizza.com and just loomer.  The first name is
  the full hostname of the system, called the "Fully Qualified Domain
  Name", and the second is an alias for it. The second allows you to
  type only rlogin loomer instead of having to type the entire hostname.
  You should ensure that you put the Fully Qualified Domain Name in the
  line before the alias name.


  11.4.2.  named - do I need thee ?

  `I dub thee ..'

  named is the nameserver daemon for many unix-like operating systems.
  It allows your machine to serve the name lookup requests, not only for
  itself, but also for other machines on the network, that is, if
  another machine wants to find the address for `goober.norelco.com',
  and you have this machines address in your named database, then you
  can service the request and tell other machines what `goobers' address
  is.

  Under older implementations of Linux tcp/ip, to create aliases for
  machine names, (even for your own machine), you had to run named on
  your Linux machine to do the hostname to IP address conversion. One
  problem with this is that named is comparitively difficult to set up
  properly, and maintain.  To solve this problem, a program called
  hostcvt.build was made available on Linux systems to translate your
  /etc/hosts file into the many files that make up named database files.
  However even with this problem overcome, named still uses CPU overhead
  and causes network traffic.

  The bottom line is this: You do not need to run named on your Linux
  system. The SLS instructions will probably tell you to run
  hostcvt.build to setup named. This is simply unnecessary unless you
  want to make your Linux system function as a nameserver for other
  machines, in which case you probably should learn some more about
  named anyway. When looking up hostnames, your linux machine will first
  check the /etc/hosts file, and then ask the nameserver out on the net.

  The only reason you may want to run named would be if:


  o  You're setting up a network of machines, and need a nameserver for
     one of them, and don't have a nameserver out on the net somewhere.

  o  Your network administrators want you to run your Linux system as a
     nameserver for some reason.

  o  You have a slow slip connection, and want to run a small cache-only
     nameserver on your Linux machine so that you don't have to go out
     on the serial line for every name lookup that occurs. If you're
     only going to be connecting to a small number of hosts on the net,
     and you know what their addresses are, then you can put them in
     your hosts file and not need to query a nameserver at all.
     Generally namelookup isn't that slow and should work fine over a
     slip link anyway.

  o  You want to run a nameserver for fun and excitement.

  In general, you do NOT need to run named: this means that you can
  comment it out from your rc.inet2 file, and you don't have to run
  hostcvt.build. If you want to alias machine names, for example, if you
  want to refer to loomer.vpizza.com as just loomer, then you can add as
  alias in /etc/hosts instead. There is no reason to run named unless
  you have a specific requirement to do so. If you have access to a
  nameserver, (and your network administrators will tell you its
  address), and most networks do, then don't bother running named.

  If you're only using loopback, you can run named and set your
  nameserver address to 127.0.0.1, but since you are the only machine
  you can talk to, this would be quite bizzarre, as you'd never need to
  call it.


  11.4.3.  /etc/networks

  The /etc/networks file lists the names and addresses of your own, and
  other, networks. It is used by the route command, and allows you to
  specify a network by name, should you so desire.

  Every network you wish to add a route to using the route command
  should have an entry in the /etc/networks file, unless you also
  specify the -net argument in the route command line.

  Its format is simliar to that of /etc/hosts file above, and an example
  file might look like:



       #
       # /etc/networks: list all networks that you wish to add route commands
       #                for in here
       #
       default         0.0.0.0         # default route    - recommended
       loopnet         127.0.0.0       # loopback network - recommended
       mynet           128.253.154.0   # Example network CHANGE to YOURS
       #
       # end of networks





  11.4.4.  /etc/host.conf

  The system has some library functions called the resolver library.
  This file specifies how your system will lookup host names. It should
  contain at least the following two lines:



       order hosts,bind
       multi on




  These two lines tell the resolve libraries to first check the
  /etc/hosts file, and then to ask the nameserver (if one is present).
  The multi entry allows you to have multiple IP addresses for a given
  machine name in /etc/hosts.

  This file comes from the implementation of the resolv+ bind library
  for Linux. You can find further documentation in the resolv+(8) man
  page if you have it. If you don't, it can be obtained from:

  sunsite.doc.ic.ac.uk


       /computing/comms/tcpip/nameserver/resolv+/resolv+2.1.1.tar.Z




  This file contains the resolv+.8 man page for the resolver library.


  11.4.5.  /etc/resolv.conf

  This file actually configures the system name resolver, and contains
  two types of entries: The addresses of your nameservers (if any), and
  the name of your domain, if you have one. If you're running your own
  nameserver (i.e running named on your Linux machine), then the address
  of your nameserver is 127.0.0.1, the loopback address.

  Your domain name is your fully qualified hostname (if you're a
  registered machine on the Internet, for example), with the hostname
  component removed.  That is, if your full hostname is
  loomer.vpizza.com, then your domain name is vpizza.com, without the
  hostname loomer.

  For example, if you machine is goober.norelco.com, and has a
  nameserver at the address 128.253.154.5, then your /etc/resolv.conf
  file would look like:



       domain norelco.com
       nameserver 127.253.154.5




  You can specify more than one nameserver. Each one must have a
  nameserver entry in the resolv.conf file.

  Remember, if you're running on loopback, you don't need a nameserver.


  11.4.6.  Configuring your Hostname - /etc/HOSTNAME

  After you have configured everything else, there is one small task
  that remains, you need to configure your own machine with a name. This
  is so that application programs like sendmail can know who you are to
  accept mail, and so that your machine can identify itself to other
  machines that it might be connected to.

  There are two programs that are used to configure this sort of
  information, and they are commonly misused. They are hostname and
  domainname.

  If you are using a release of net-tools earlier than 1.1.38 then you
  can include a command in your /etc/rc file that looks like this:


       /bin/hostname -S




  and this will cause the hostname command to read a file called
  /etc/HOSTNAME which it expects will contain a "Fully Qualified Domain
  Name", that is, your machines hostname including the domainname. It
  will split the F.Q.D.N. into its DNS hostname and domainname
  components and set them appropriately for you.

  For example, the machine above would have the file /etc/HOSTNAME:



       goober.norelco.com




  If you are using the hostname that came with net-tools-1.1.38 or
  later, then you would add a command at the end of your
  /etc/rc.d/rc.inet1 file like:



       /bin/hostname goober.norelco.com




  or if you have upgraded from a previous release, you could add:



       /bin/hostname -F /etc/HOSTNAME




  and it would behave in the same way as for the earlier version.

  The /bin/domainname command is for setting the N.I.S.  domain name NOT
  the D.N.S. domain name. You do not need to set this unless you are
  running NIS, which is briefly described later.


  11.5.  Other files.

  There are of course many other files in the /etc directory which you
  may need to dabble with later on. Instead of going into them here, I'm
  going to provide the bare minimum to get you on the net. More
  information is available in Olaf's Network Administration Guide. It
  picks up where this HOWTO ends, and some more information will be
  provided in later versions of this document.

  Once you have all of the files set up, and everthing in the right
  place, you should be able to reboot you new kernel, and net away to
  your hearts content.  However I strongly suggest that you keep a
  bootable copy of your old kernel and possibly even a `recovery disk',
  in case something goes wrong, so that you can get back in and fix it.
  You might try HJLu's `single disk boot disk', or `disk1' from an SLS
  distribution.



  12.  Advanced Configurations.

  The configurations above have described how a typical Linux
  workstation might be configured for normal end-user operation. Some of
  you will have other requirements which will require slightly more
  advanced configurations. What follows are examples of some the more
  common of these.

  The details of the AX.25, Ottawa PI and generic SCC drivers have been
  moved to the HAM-HOWTO <http://sunsite.unc.edu/mdw/HOWTO/HAM-
  HOWTO.html>.


  12.1.  PPP - Point to Point Protocol.

  The Point to Point Protocol is a modern and efficient protocol for
  conveying multiple protocols, tcp/ip for one, across serial links,
  that a lot of people use in place of slip. It offers enhanced
  functionality, error detection and security options. It corrects a
  number of deficiencies that are found in slip, and is suitable for
  both asynchronous links and synchronous links alike.

  An important feature of PPP operation is dynamic address allocation,
  and this feature will almost certainly be exploited by your PPP
  server. This feature allows a PPP client, with a specially formatted
  frame, to request its address from the server. In this way
  configuration is somewhat less messy than with slip, since this
  ability to retrieve your address must occur outside of the protocol.

  The authors of the Linux port are Michael Callahan,
  <[e-mail]> and  Al Longyear, <[e-mail]>.
  Most of this information has come from the documentation that
  accompanies the PPP software. The documentation is quite complete, and
  will tell you much more than I present here.

  The Linux PPP code has come out of Alpha testing and is now available
  as a public release. The 1.0.0 Linux PPP code is based on Paul
  Mackerras's free PPP for BSD-derivative operating systems. The 1.0.0
  release is based on version 2.1.1 of the free PPP code.

  The PPP code comes in two parts. The first is a kernel module which
  handles the assembly and disassembly of the frames, and the second is
  a set of protocols called LCP, IPCP, UPAP and CHAP, for negotiating
  link options, bringing the link into a functioning state and for
  authentication.


  12.1.1.  Why would I use PPP in place of SLIP ?

  You would use PPP in place of SLIP for a few reasons. The most common
  are:


     Your Internet Provider supports only PPP
        The most obvious reason you would use PPP in favour of SLIP is
        when your Internet Provider supports PPP and not SLIP. Ok, I
        said it was obvious.

     You have a normally noisy serial line
        PPP provides a frame check sequence for each and every frame
        transmitted, SLIP does not. If you have a noisy serial line, and
        you are using SLIP, your error correction will be performed end
        to end, that is between your machine and the destination
        machine, whereas with PPP the error detection occurs locally,
        between your machine and the PPP server. This makes for faster
        recovery from errors.
     You need to make use of some other feature PPP offers.
        PPP provides a number of features that SLIP does not. You might
        for example want to carry not only IP, but also DECNET, or
        AppleTalk frames over your serial link. PPP will allow you to do
        this.


  12.1.2.  Where to obtain the PPP software.

  The ppp software is available from:

  sunsite.unc.edu


       /pub/Linux/system/Networking/serial/ppp-2.1.2d.tar.gz




  This file contains the kernel source, and the pppd source and binary.
  Version 1.0.0 is meant for use with kernels 1.0.x and 1.1.x.


  12.1.3.  Installing the PPP software.

  Installation of the PPP software is fairly straightforward.


  12.1.3.1.  The kernel driver.

  Some support for ppp has been built into the kernel for some time.  so
  you are advised to run a modern kernel. Configuring the kernel is
  fairly easy, the following should work ok:



       # make config   (remembering to answer yes to PPP support)
       # make dep
       # make          (remember to install the new kernel after recompiling!)




  When you reboot with the new kernel you should see messages at boot
  time that look something like these:



       PPP: version 0.2.7 (4 channels) NEW_TTY_DRIVERS OPTIMIZE_FLAGS
       TCP compression code copyright 1989 Regents of the University of California
       PPP line discipline registered.




  These indicate that the PPP support has in fact been compiled into
  your kernel.

  Now, try looking at the contents of /proc/net/dev. You should be
  careful not to use more or less on the files in the /proc filesystem,
  as some of them check the filesize first and it is a feature of the
  /proc filesystem that the files are zero length, so use:


       # cat /proc/net/dev

  It should look something like this:



       Inter-|   Receive                  |  Transmit
        face |packets errs drop fifo frame|packets errs drop fifo colls carrier
       lo:        0    0    0    0    0        0    0    0    0     0    0
       ppp0:      0    0    0    0    0        0    0    0    0     0    0
       ppp1:      0    0    0    0    0        0    0    0    0     0    0
       ppp2:      0    0    0    0    0        0    0    0    0     0    0
       ppp3:      0    0    0    0    0        0    0    0    0     0    0




  This indicates that the kernel driver is installed correctly.


  12.1.3.2.  pppd

  To extract the ppp software and associated utilities the following
  should work ok:



       # cd /usr/src
       # gzip -dc ppp-2.1.2d.tar.gz | tar xvf -




  If you want to recompile pppd, type make in the pppd subdirectory of
  the installation.  There will be some warnings when compiling lcp.c,
  upap.c and chap.c but these are OK.

  If you want to recompile chat, consult README.linux in the chat
  directory.

  To install, type make install in the chat and pppd directories.   This
  will put chat and pppd binaries in /usr/sbin and the pppd.8 manual
  page in /usr/man/man8.

  pppd needs to be run as root. You can either make it suid root or just
  use it when you are root. make install will try to install it suid
  root, so if you are root when you try to install it, it should work
  ok.


  12.1.4.  Configuring and using the PPP software.

  Like slip, you can configure the PPP software as either a client or a
  server.  The chat program performs a similar function to the dip
  program in that it is used to automate the dialling and login
  procedure to the remote machine, unlike dip though, it does not
  perform the ioctl to convert the serial line into a PPP line. This is
  performed by the pppd program. pppd can act as either the client or
  the server. When used as a client, it normally invokes the chat
  program to perform the connection and login, and then it takes over by
  performing the ioctl to change the line discipline to ppp, performs a
  number of steps in configuring your machine to talk to the remote
  machine and then steps out of the way to let you operate.

  Please refer to the pppd and chat man pages for more information.
  Please also refer to the README file that comes with the ppp software,
  as its description of the operation of these utilities is much more
  complete than I have described here.
  12.1.4.1.  Configuring a PPP client by dial-up modem.

  This is perhaps what most of you will want to do, so it appears first.
  You would use this configuration when you have a network provider who
  supports ppp by dialup modem. When you want to establish your
  connection you simply have to invoke the pppd program with appropriate
  arguments.

  The following example might look a little confusing at first, but it
  is easier to understand if you can see that all it is doing is taking
  a command line for the chat program as its first argument and then
  others for itself later.



       pppd connect 'chat -v "" ATDT5551212 CONNECT "" ogin: ppp word: password'\
       /dev/cua1 38400 debug crtscts modem defaultroute 192.1.1.17:




  What this says is:


  o  Invoke the chat program with the command line:


       chat -v "" ATDT5551212 CONNECT "" ogin: ppp word: password




  Which says: Dial 5551212, wait for the `CONNECT' string, transmit a
  carriage return, wait for the string `ogin:', transmit the string
  `ppp', wait for the string `word:', transmit the string `password',
  and quit.

  o  Use serial device /dev/cua1

  o  Set its speed to 38400 bps.

  o  debug means log status messages to syslog

  o  crtscts means use hardware handshaking to the modem - recommended.

  o  modem means that pppd will attempt to hang up the call before and
     after making the call.

  o  defaultroute instructs pppd to add a routing entry that makes this
     the default route. In most cases this will be what you want.

  o  192.1.1.17: says to set the ppp interfaces address to 192.1.1.17.
     This argument normally looks like x.x.x.x:y.y.y.y, where x.x.x.x is
     your ip address, and y.y.y.y is the ip address of the server. If
     you leave off the server's address, pppd will ask for it, and
     x.x.x.x will be set to your machines ip address.

  Please refer to the pppd and chat man pages for more information.
  Please also refer to the README file that comes with the ppp software,
  as its description of the above is much more complete than I have
  described here.





  12.1.4.2.  Configuring a PPP client via a leased line.

  Configuring a PPP client via a leased line is very simple. You will
  still use the pppd program, but since you won't need to establish the
  modem link the arguments to the chat program can be much simpler.

  The example I'm presenting here assumes that the ppp server doesn't
  require any special login procedure. I do this because every login
  procedure will be different, and if you are simply running a local
  connection then it is possible that you might have it set up this way.



       pppd defaultroute noipdefault debug \
       kdebug 2 /dev/cua0 9600




  This will open the serial device, generate the ioctl to change it into
  a pppdevice, set your default route via the ppp interface.  The
  noipdefault argument instructs the pppd program to request the address
  to use for this device from the server. Debug messages will go to
  syslog. The kdebug 2 argument causes the debug messages to be set to
  level 2, this will give you slightly more information on what is going
  on. It will use /dev/cua0 at 9600 bps.

  If your ppp server does require some sort of login procedure, you can
  easily use the chat program as in the example for the dialup server to
  perform that function for you.

  Please refer to the pppd and chat man pages for more information.
  Please also refer to the README file that comes with the ppp software,
  as its description of the above is much more complete than I have
  described here.


  12.1.4.3.  Configuring a PPP server.

  Configuring a PPP server is similar to establishing a slip server.
  You can create a special `ppp' account, which uses an executable
  script as its login shell. The /etc/passwd entry might look like:



       ppp:EncPasswd:102:50:PPP client login:/tmp:/etc/ppp/ppplogin




  and the /etc/ppp/ppplogin script might look like:



       #!/bin/sh
       exec /usr/sbin/pppd passive :192.1.2.23




  The address that you provide will be the address that the calling
  machine will be assigned.

  Naturally, if you want multiple users to have simultaneous access you
  would have to create a number of startup scripts and individual
  accounts for each to use, as you can only put one ip address in each
  script.


  12.1.5.  Where to obtain more information on PPP, or report bugs.

  Most discussion on PPP for Linux takes place on the PPP mailing list.

  To join the Linux linux-ppp channel on the mail list server, send mail
  to:



       [e-mail]

       with the line:

       subscribe linux-ppp

       in the message body. The subject line is ignored.




  Please remember that when you are reporting bugs or problems you
  should include as much information relevant to the problem as you can
  to assist those that will help you understand your problem.

  You might also like to check out:

  RFCS 1548, 1331, 1332, 1333, and 1334. These are the definitive
  documents for PPP.

  W. Richard Stevens also describes PPP in his book `TCP/IP Illustrated
  Volume 1', (Addison-Wessley, 1994, ISBN 0-201-63346-9).


  12.2.  Configuring Linux as a Slip Server.

  If you have a machine that is perhaps network connected, that you'd
  like other people be able to dial into, and provide network services,
  then you will need to configure your machine as a server. If you want
  to use slip as the serial line protocol, then currently you have three
  options as to how to configure your Linux machine as a slip server. My
  preference would be to use the first presented, sliplogin, as it seems
  the easiest to configure and understand, but I will present a summary
  of each, so you make your mind.


  12.2.1.  Slip Server using sliplogin.

  sliplogin is a program that you can use in place of the normal login
  shell for slip users that converts the terminal line into a slip line.
  It allows you to configure your Linux machine as either a static
  address server, users get the same address everytime they call in, or
  a dynamic address server, where users get an address allocated for
  them which will not necessarily be the same as the last time they
  called.

  The caller will login as per the standard login process, entering
  their username and password, but instead of being presented with a
  shell after their login, sliplogin is executed which searches its
  configuration file (/etc/slip.hosts) for an entry with a login name
  that matches that of the caller. If it locates one, it configures the
  line as an 8bit clean line, and uses an ioctl call to convert the line
  discipline to slip. When this process is complete, the last stage of
  configuration takes place, where sliplogin invokes a shell script
  which configures the slip interface with the relevant ip address,
  netmask and sets appropriate routing in place.  This script is usually
  called /etc/slip.login, but in a similar manner to getty, if you have
  certain callers that require special initialisation, then you can
  create configuration scripts called /etc/slip.login.loginname that
  will be run instead of the default specifically for them.

  There are either three or four files that you need to configure to get
  sliplogin working for you. I will detail how and where to get the
  software, and how each is configured in detail. The files are:


  o  /etc/passwd, for the dialin user accounts.

  o  /etc/slip.hosts, to contain the information unique to each dial-in
     user.

  o  /etc/slip.login, which manages the configuration of the routing
     that needs to be performed for the user.

  o  /etc/slip.tty, which is required only if you are configuring your
     server for dynamic address allocation and contains a table of
     addresses to allocate

  o  /etc/slip.logout, which contains commands to clean up after the
     user has hung up or logged out.


  12.2.1.1.  Where to get sliplogin

  sliplogin can be obtained from:

  sunsite.unc.edu


       /pub/Linux/system/Network/serial/sliplogin-1.3.tar.gz




  The tar file contains both source, precompiled binaries and a man
  page.

  To ensure that only authorised users will be able to run sliplogin
  program, you should add an entry to your /etc/group file similar to
  the following:



        ..
       slip::13:radio,fred
        ..




  When you install the sliplogin package, the Makefile will change the
  group ownership of the sliplogin program to slip, and this will mean
  that only users who belong to that group will be able to execute it.
  The example above will allow only users radio and fred to execute
  sliplogin.

  To install the binaries into your /sbin directory, and the man page
  into section 8, do the following:


       # cd /usr/src
       # gzip -dc .../sliplogin-1.3.tar.gz | tar xvf -
       # cd src
       # make install




  If you want to recompile the binaries before installation, add a make
  clean before the make install. If you want to install the binaries
  somewhere else, you will need to edit the Makefile install rule.

  Please read the README files that come with the package for more
  information.


  12.2.1.2.  Configuring /etc/passwd for Slip hosts.

  Normally you would create some special logins for Slip callers in your
  /etc/passwd file. A convention commonly followed is to use the
  hostname of the calling host with a capital `S' prefixing it. So, for
  example, if the calling host is called radio then you could create a
  /etc/passwd entry that looked like:



       Sradio:FvKurok73:1427:1:radio slip login:/tmp:/sbin/sliplogin




  It doesn't really matter what the account is called, so long as it is
  meaningful to you.

  Note: the caller doesn't need any special home directory, as they will
  not be presented with a shell from this machine, so /tmp is a good
  choice.  Also note that sliplogin is used in place of the normal login
  shell.


  12.2.1.3.  Configuring /etc/slip.hosts

  The /etc/slip.hosts file is the file that sliplogin searches for
  entries matching the login name to obtain configuration details for
  this caller. It is this file where you specify the ip address and
  netmask that will be assigned to the caller, and configured for their
  use. Sample entries for two hosts, one a static configuration for host
  radio, and another, a dynamic configuration for user host albert might
  look like:



       #
       Sradio    44.136.8.99    44.136.8.100   0xffffff00   normal
       Salbert   44.136.8.99    DYNAMIC        0xffffff00   compressed
       #




  The /etc/slip.hosts file entries are:


  1. the login name of the caller.


  2. ip address of the server machine, ie this machine.

  3. ip address that the caller will be assigned. If this field is coded
     DYNAMIC then an ip address will be allocated based on the
     information contained in your /etc/slip.tty file discussed later.
     Note: you must be using at least version 1.3 of sliplogin for this
     to work.

  4. the netmask assigned to the calling machine in hexadecimal notation
     eg 0xffffff00 for a Class C network mask.

  5. optional parameters to enable/disable compression and other
     features.

  Note: You can use either hostnames or IP addresses in dotted decimal
  notation for fields 2 and 3. If you use hostnames then those hosts
  must be resolvable, that is, your machine must be able to locate an ip
  address for those hostnames, otherwise the script will fail when it is
  called. You can test this by trying trying to telnet to the hostname,
  if you get the Trying nnn.nnn.nnn... message then your machine has
  been able to find an ip address for that name. If you get the message
  Unknown host, then it has not. If not, either use ip addresses in
  dotted decimal notation, or fix up your name resolver configuration
  (See section Name Resolution).

  The most commonly used optional paramaters for the opt1 and opt2
  fields are:


     normal
        to enable normal uncompressed slip.

     compressed
        to enable van Jacobsen header compression (cslip)

  Naturally these are mutually exclusive, you can use one or the other.
  For more information on the other options available, refer to the man
  pages.


  12.2.1.4.  Configuring the /etc/slip.login file.

  After sliplogin has searched the /etc/slip.hosts and found a matching
  entry, it will attempt to execute the /etc/slip.login file to actually
  configure the slip interface with its ip address and netmask.

  The sample /etc/slip.login file supplied with the sliplogin package
  looks like this:



       #!/bin/sh -
       #
       #       @(#)slip.login  5.1 (Berkeley) 7/1/90
       #
       # generic login file for a slip line.  sliplogin invokes this with
       # the parameters:
       #     $1       $2        $3       $4         $5        $6    $7-n
       #   slipunit ttyspeed loginname local-addr remote-addr mask opt-args
       #
       /sbin/ifconfig $1 $4 pointopoint $5 mtu 1500 -trailers up
       /sbin/route add $5
       arp -s $5 <hw_addr> pub
       exit 0
       #

  You will note that this script simply uses the ifconfig and route
  commands to configure the slip device with its ipaddress, remote ip
  address and netmask, and creates a route for the remote address via
  the slip device. Just the same as you would if you were using the
  slattach command.

  Note also the use of Proxy ARP to ensure that other hosts on the same
  ethernet as the server machine will know how to reach the dial-in
  host.  The <hw_addr> field should be the hardware address of the
  ethernet card in the machine. If your server machine isn't on an
  ethernet network then you can leave this line out completely.


  12.2.1.5.  Configuring the /etc/slip.logout file.

  When the call drops out, you want to ensure that the serial device is
  restored to its normal state so that future callers will be able to
  login correctly.  This is achieved with the use of the
  /etc/slip.logout file. It is quite simple in format.



       #!/bin/sh -
       #
       #               slip.logout
       #
       /sbin/ifconfig $1 down
       /sbin/route del $5
       arp -d $5
       exit 0
       #




  All it does is `down' the interface and delete the manual route
  previously created. It also uses the arp command to delete any proxy
  arp put in place, again, you don't need the arp command in the script
  if your server machine does not have an ethernet port.


  12.2.1.6.  Configuring the /etc/slip.tty file.

  If you are using dynamic ip address allocation (have any hosts
  configured with the DYNAMIC keyword in the /etc/slip.hosts file, then
  you must configure the /etc/slip.tty file to list what addresses are
  assigned to what port. You only need this file if you wish your server
  to dynamically allocate addresses to users.

  The file is a table that lists the tty devices that will support dial-
  in slip connections and the ip address that should be assigned to
  users who call in on that port.

  Its format is as follows:


       # slip.tty    tty -> IP address mappings for dynamic SLIP
       # format: /dev/tty?? xxx.xxx.xxx.xxx
       #
       /dev/ttyS0      192.168.0.100
       /dev/ttyS1      192.168.0.101
       #




  What this table says is that callers that dial in on port /dev/ttyS0
  who have their remote address field in the /etc/slip.hosts file set to
  DYNAMIC will be assigned an address of 192.168.0.100.

  In this way you need only allocate one address per port for all users
  who do not require an dedicated address for themselves. This helps you
  keep the number of addresses you need down to a minimum to avoid
  wastage.


  12.2.2.  Slip Server using dip.

  Let me start by saying that some of the information below came from
  the dip man pages, where how to run Linux as a slip server is briefly
  documented. Please also beware that the following has been based on
  the dip337j-uri.tgz package and probably will not apply to other
  versions of dip.

  dip has an input mode of operation, where it automatically locates an
  entry for the user who invoked it and configures the serial line as a
  slip link according to information it finds in the /etc/diphosts file.
  This input mode of operation is activated by invoking dip as diplogin.
  This therefore is how you use dip as a slip server, by creating
  special accounts where diplogin is used as the login shell.

  The first thing you will need to do is to make a symbolic link as
  follows:



       # ln -sf /usr/sbin/dip /usr/sbin/diplogin




  You then need to add entries to both your /etc/passwd and your
  /etc/diphosts files. The entries you need to make are formatted as
  follows:

  To configure Linux as a slip server with dip, you need to create some
  special slip accounts for users, where dip (in input mode) is used as
  the login shell. A suggested convention is that of having all slip
  accounts begin with a capital `S', eg `Sfredm'.

  A sample /etc/passwd entry for a slip user looks like:



       Sfredm:ij/SMxiTlGVCo:1004:10:Fred:/tmp:/usr/sbin/diplogin
       ^^         ^^        ^^  ^^   ^^   ^^   ^^
       |          |         |   |    |    |    \__ diplogin as login shell
       |          |         |   |    |    \_______ Home directory
       |          |         |   |    \____________ User Full Name
       |          |         |   \_________________ User Group ID
       |          |         \_____________________ User ID
       |          \_______________________________ Encrypted User Password
       \__________________________________________ Slip User Login Name




  After the user logs in, the login(1) program, if it finds and verifies
  the user ok, will execute the diplogin command. dip, when invoked as
  diplogin knows that it should automatically assume that it is being
  used a login shell. When it is started as diplogin the first thing it
  does is use the getuid() function call to get the userid of whoever
  has invoked it. It then searches the /etc/diphosts file for the first
  entry that matches either the userid or the name of the tty device
  that the call has come in on, and configures itself appropriately.  By
  judicious decision as to whether to give a user an entry in the
  diphosts file, or whether to let the user be given the default
  configuration you can build your server in such a way that you can
  have a mix of static and dynamically assigned address users.

  dip will automatically add a `Proxy-ARP' entry if invoked in input
  mode, so you do not need to worry about manually adding such entries.


  12.2.2.1.  Configuring /etc/diphosts

  /etc/diphosts is used by dip to lookup preset configurations for
  remote hosts. These remote hosts might be users dialing into your
  linux machine, or they might be for machines that you dial into with
  your linux machine.

  The general format for /etc/diphosts is as follows:



        ..
       Suwalt::145.71.34.1:145.71.34.2:255.255.255.0:SLIP uwalt:CSLIP,1006
       ttyS1::145.71.34.3:145.71.34.2:255.255.255.0:Dynamic ttyS1:CSLIP,296
        ..




  The fields are:

  1. login name: as returned by getpwuid(getuid()) or tty name.

  2. unused: compat. with passwd

  3. Remote Address: IP address of the calling host, either numeric or
     by name

  4. Local Address: IP address of this machine, again numeric or by name

  5. Netmask: in dotted decimal notation

  6. Comment field: put whatever you want here.

  7. protocol: Slip, CSlip etc.

  8. MTU: decimal number

  An example /etc/net/diphosts entry for a remote slip user might be:



       Sfredm::145.71.34.1:145.71.34.2:255.255.255.0:SLIP uwalt:SLIP,296




  which specifies a slip link with remote address of 145.71.34.1, and
  MTU of 296, or:



       Sfredm::145.71.34.1:145.71.34.2:255.255.255.0:SLIP uwalt:CSLIP,1006

  which specifies a cslip-capable link with remote address 145.71.34.1,
  and MTU of 1006.

  Therefore, all users who you wish to be allowed a statically allocated
  dial-up IP access should have an entry in the /etc/diphosts and if you
  want users who call a particular port to have their details
  dynamically allocated you must have an entry for the tty device and do
  not configure a user based entry. You should remember to configure at
  least one entry for each tty device that your dialup users use to
  ensure that a suitable configuration is available for them regardless
  of which modem they call in on.

  When a user logs in, they will receive a normal login and password
  prompt, at which they should enter their slip-login userid and
  password. If they check out ok, then the user will see no special
  messages, they should just change into slip mode at their end, and
  then they should be able to connect ok, and be configured with the
  parameters from the diphosts file.


  12.2.3.  slip server using the dslip package.

  Matt Dillon <[e-mail]> has written a package that
  does not only dial-in but also dial-out slip. Matt's package is a
  combination of small programs and scripts that manage your connections
  for you. You will need to have tcsh installed as at least one of the
  scripts requires it. Matt supplies a binary copy of the expect utility
  as it too is needed by one of the scripts. You will most likely need
  some experience with expect to get this package working to your
  liking, but don't let that put you off.

  Matt has written a good set of installation instructions in the README
  file, so I won't bother repeating them.

  You can get the dslip package from its home site at:

  apollo.west.oic.com


       /pub/linux/dillon_src/dslip203.tgz




  or from:

  sunsite.unc.edu


       /pub/Linux/system/Network/serial/dslip203.tgz




  Read the README file, and create the /etc/passwd and /etc/group
  entries before doing a make install.



  12.3.  Using the Automounter Daemon - AMD.

  This section has been supplied by Mitch DSouza, and I've included it
  with minimal editing, as he supplied it. Thanks Mitch.



  12.3.1.  What is an automounter, and why would I use one ?

  An automounter provides a convenient means of mounting filesystems on
  demand, i.e. when requried. This will reduce both the server and the
  client load, and provides a great deal of flexibility even with non-
  NFS mounts. It also offers a redundancy mechanism whereby a mount
  point will automatically switch to a secondary server should a primary
  one be unavailable. A rather useful mount called the union mount gives
  the automounter the ability to merge the contents of multiple
  directories into a single directory. The documentation msut be read
  thoroughly to make full use of its extensive capabilities.

  A few important points must be remembered - (in no particular order):


  o  amd maps are not compatible with Sun maps, which in turn are not
     compatible with HP maps ad infinitum. The point here however is
     that amd is freely available and compatible with all the systems
     mentioned above and more, thus giving you the ability to share maps
     if amd is installed throughout your network. Mitch uses it with a
     mixture of Linux/Dec/NeXt/Sun machines.

  o  Sun automount maps can be converted to amd style maps by using the
     perl script in the contrib directory - automount2amd.pl.

  o  You must have the portmapper running before starting amd.

  o  UFS mounts do not timeout.

  o  UFS mounts, in the case of Linux only, have been extended to deal
     with all varieties of native filesystems (i.e. minix, ext, ext2,
     xiafs ...) with the default being minix. This undocumented feature
     is accessed in the opts option like:


        ..., opts:=type=msdos,conv=auto




  o  Do not mount over existing directories unless you use a direct
     automount option, otherwise it is like mounting your disk on /home
     when some user directory is /home/fred.

  o  Always turn on full logging with the `-x all' option to amd if you
     have any troubles. Check also what the command:


       % amq -ms




  reports, as it will indicate problems as they occur.

  o  GNU getopt() is too clever for its own good sometimes. You should
     always use `--' before the non-options e.g.


       # /etc/amd -x all -l syslog -a /amd -- /net /etc/amd.net






  12.3.2.  Where to get AMD, the automounter daemon.

  amd can be obtained from:

  sunsite.unc.edu


       /pub/Linux/system/Misc/mount/amd920824upl67.tar.gz




  This contains ready-to-run binaries, full sources and documentation in
  texinfo format.


  12.3.3.  An example AMD configuration.

  You do not configure the automounter from the /etc/fstab file, which
  you will already be using to contain information about your
  fileystems, instead it is command line driven.

  To mount two nfs filesystems using your /etc/fstab file you would use
  two entries that looked like:



       server-1:/export/disk  /nfs/server-1  nfs  defaults
       server-2:/export/disk  /nfs/server-2  nfs  defaults




  i.e. you were nfs mounting server-1 and server-2 on your linux disk on
  the /nfs/server-1 and /nfs/server-2 directories.

  After commenting out, or deleting the above lines from your /etc/fstab
  file, you could amd to perform the same task with the following
  syntax:



       /etc/amd -x all -l syslog -a /amd -- /nfs /etc/amd.server
       |      | |    | |       | |     |  | |  | |             |
       |      | |    | |       | |     |  | |  | |             |
       `------' `----' `-------' `-----' -' `--' `-------------'
       |        |      |         |      |   |    |
       (1)      (2)    (3)       (4)    (5) (6)  (7)




  Where:


  1. The full amd binary path (obviously optional) depending on your
     $PATH setting, so just `amd' may be specified here.

  2. `-x all' means turn full logging on. Read the documentation for the
     other logging levels

  3. `-l syslog' means log the message via the syslog daemon. This could
     mean put it to a file, dump it, or pass it, to an unused tty
     console. This (syslog) can be changed to the name of a file, i.e.
     `-l foo' will record to a file called foo.

  4. `-a /amd' means use the /amd directory as a temporary place for
     automount points. This directory is created automatically by amd
     and should be removed before starting amd in your /etc/rc scripts.

  5. `--' means tell getopt() to stop attempting to parse the rest of
     the command line for options. This is especially useful when
     specifying the `type:=' options on the command line, otherwise
     getopt() tries to decode it incorrectly.

  6. `/nfs' is the real nfs mount point. Again this is automatically
     created and should not generally contain subdirectories unless the
     `type:=direct' option is used.

  7. The amd map (i.e. a file) named `amd.server' contains the lines:



       # /etc/amd.server
       /defaults    opts:=rw;type:=nfs
       server-1     rhost:=server-1;rfs:=/export/disk
       server-2     rhost:=server-2;rfs:=/export/disk





  Once started and successfully running, you can query the status of the
  mounts with the command:



       % amq -ms




  Now if you say:



       % ls /nfs




  you should see no files. However the command:



       % ls /nfs/server-1




  will mount the host `server-1' automatically. voila! amd is running.
  After the default timeout has expired, this will automatically be
  unmounted. Your /etc/password file could contain entries like:



        ...
       linus:EncPass:10:0:God:/nfs/server-1/home/linus:/bin/sh
       mitch:EncPass:20:10:Mitch DSouza:/nfs/server-1/home/mitch:/bin/tcsh
       matt:EncPass:20:10:Matt Welsh:/nfs/server-1/home/matt:/bin/csh


  which would mean that when Linus, Matt, or Mitch are logged in, their
  home directory will be remotely mounted from the appropriate server,
  and umounted when they log out.


  12.4.  Using Linux as a router

  Linux will function just fine as a router. You should run a routing
  daemon such as gated, or if you have simple routing requirements use
  hard coded routes. If you are using a late version kernel (1.1.*) then
  you should ensure that you have answered `y' to:



       IP forwarding/gatewaying (CONFIG_IP_FORWARD) [y] y




  when building your kernel.

  Olaf Kirch's Network Administrators Guide discusses network design and
  routing issues, and you should read it for more information. A
  reference to it is in the "Related Documentation" section of this
  document.


  12.5.  NIS - Sun Network Information System.

  There is now an NIS-HOWTO <http://sunsite.unc.edu/mdw/HOWTO/NIS-
  HOWTO.html> which you should read if you are interested in using NIS.
  It details how to obtain, install and configure the NIS system for
  Linux.



  13.  Experimental and Developmental modules.

  There are a number of people developing new features and modules for
  the Linux networking code. Some of these are in quite an advanced
  state (read working), and it is these that I intend to include in this
  section until they are standard release code, when they will be moved
  forward.

  The AX25 section has been relocated into the HAM-HOWTO
  <http://sunsite.unc.edu/mdw/HOWTO/HAM-HOWTO.html> because it was
  fairly specific to Amateur Radio.


  13.1.  snmp agent.

  There is an experimental snmp agent for linux, ported from the cmu-
  snmp source by Erik Schoenfelder, <[e-mail]>.

  It is available from:

  ftp.ibr.cs.tu-bs.de


       /pub/local/cmu-snmp2.1.2l3-src.tar.gz




  Please read the file called cmu-snmp2.1.2l3.README, as it contains
  information that you will need to know about the package.
  This package provides a nearly complete MIB-II variable set. and parts
  of the host MIB. Setting of system group variables is provided. The
  private community string is setable in the config file.

  nstat.tar.gz contains a formatter of the output from /proc/net/snmp
  called nstat.

  You will need Linux v1.1.60 and libc v4.6.27 or higher to compile and
  run the agent.


  13.2.  Experimental Token Ring driver

  An experimental Token Ring driver is being developed by Peter De
  Schrijver <[e-mail]>. His latest version, at the time
  of writing is available in the Linux 1.3.* kernel release kernels.
  For older kernel versions the driver patches are located at:

  linux3.cc.kuleuven.ac.be


       /pub/Linux/TokenRing/TokenRing.patch-1.2.0.gz




  ftp.cs.kuleuven.ac.be


       /pub/unix/linux/TokenRing.patch-1.1.64.gz




  There are a number of patch files against various kernel versions.
  Just pick the one that suits your kernel.

  Note also that there are versions of the network tools to suit Token
  Ring in the same directory at linux3.cc.kuleven.ac.be.

  Most boards based on IBM's TROPIC chipset should work now. The
  following boards are known to be working with the driver :


  o  IBM Token Ring Adapter II

  o  IBM Token Ring 16/4 Adapter

  o  IBM Token Ring Adapter/A

  o  IBM Token Ring 16/4 Adapter/A

  o  HyperRing Classic 16/4

  Boards which use the TI chipset or busmastering DMA won't work with
  the current driver. However someone is working on a driver for the IBM
  busmaster adapters.


  13.3.  V.35 interface board

  V.35 is a C.C.I.T.T. standard interface that provides a high speed
  balanced serial interface suitable for speeds up to about 2 Mbps. The
  use of differential pair balanced transmission allows the V.35
  interface to support longer cables than can the more familiar
  V.24/RS232C type interface and higher data rates.
  13.3.1.  Internet Technologies International XNET-1

  Matti Aarnio <[e-mail]> represents Internet Technologies
  International <mailto:[e-mail]>.  They have an 8 bit X.21 card
  available called the XNET-1 which will work for V.35 with an
  appropriate cable. You can obtain information on the card itself from:


  Internet Technologies International OY,
  Helsinki, Finland  <[e-mail]>
  Internet Technologies International OY (Ltd)
  PO BOX 51
  00641 Helsinki
  FINLAND
  Fax: [phone]



  The driver for the card is available from ftp.funet.fi
  <ftp://ftp.funet.fi/pub/Linux/kernel/xnet-sync-driver.tar.gz>


  13.3.2.  SDL Communications N2 card.

  SDL Communications <http://www.ici.net/cust_pages/sdl/sdl.html>
  produce a variety of controller cards supporting V.35 for ISA based
  machines.

  The beta release driver can be found at:

  ftp.sdlcomm.com


       /business/sdlcomm/n2/linux




  For further information you can contact Rubin Dhillon at SDL Sales
  <mailto:[e-mail]>



  13.4.  IPX bridge program

  Vinod G Kulkarni <[e-mail]> has cowritten some software
  for linux that will allow it to act as an IPX bridge.

  The software is available from:

  sunsite.unc.edu


       /pub/Linux/Systems/Network/router/ipxbridge.tar.gz





  13.5.  IPX RIP and SAP support.

  Alex Liu <[e-mail] has written support for the Novell RIP and
  SAP protocols to allow your linux machine to act as a Novell router.

  This software is alpha and includes a kernel patch. Be warned that you
  should take the usual precautions when testing this software.
  You can obtain the software from:

  sunsite.unc.edu


       /pub/Linux/Incoming/ipxripd-002.tar.gz (until it is moved)
       /pub/Linux//system/Network/router/ipxripd-002.tar.gz




  A README file is included, and you should read this for installation
  and configuration details.


  13.6.  Demand Dial SLIP/PPP package

  Eric Schenk <[e-mail]> has written a demand dial daemon
  that will work with either SLIP or PPP. It relies on you having a slip
  device configured which the daemon connects to via a pty. When your
  slip connection is not active all datagrams for non local hosts will
  be routed to this device, and the daemon will detect them, when it
  receives a datagram it executes a script to activate your network
  link, and then reroutes datagrams to that link.

  The software is available at:

  sunsite.unc.edu


       /pub/Linux/system/Network/serial/diald-0.7.tar.gz




  Note: You must configure your kernel so that it includes the slip
  driver, even if you only want to run PPP.

  The included documentation describes how to install and configure the
  software.


  13.7.  ISDN support

  There are various ISDN support efforts underway. The ones that I know
  of are:


  13.7.1.  3Com-Sonix PC/Arpeggio driver

  Alan Cox has started a driver for the 3Com arpeggio ISDN card. It is
  currently capable of supporting Async PPP only.

  sunsite.unc.edu


       /pub/Linux/kernel/patches/network/sonix.tgz





  13.7.2.  DIEHL SCOM card

  sunsite.unc.edu

  /pub/Linux/kernel/patches/network/isdndrv-0.1.1.tar.gz





  13.7.3.  ICN ISDN and/or Teles ISDN card and/or Creatix AVM ISDN board

  Fritz Elfert, Jan den Ouden and Thinking Objects have written a linux
  driver for the ICN ISDN card. Some of the documentation for this
  driver is in German.  There seem to be various versions of this driver
  around that apparently support other ISDN cards, if you obtain one and
  it doesn't support your card take a look at another of the sites. You
  can obtain them from:

  ftp.franken.de


       /pub/isdn4linux/




  or: ftp.gwdg.de


       /pub/linux/misc/isdn4linux/





  13.7.4.  Euro-ISDN card ?

  Matthias Urlichs <[e-mail]> has developed some
  experimental Streams based ISDN support for Linux. The most recent
  version was for kernel version 1.3.* and is reported to work.

  It is available at:

  ftp.uni-stuttgart.de


       /pub/systems/linux/isdn/ftp.noris.de/




  Be warned, the documentation is in German, and the code is designed to
  support the european ISDN network. Matthias is working on a english
  version of the documentation.


  13.7.5.  Combinet's Everyware 1000 ISDN card

  Joel Katz <[e-mail]> has developed a driver for Combinet's
  Everyware 1000 series of plug-in ISDN cards.

  It is available from: sunsite.unc.edu


       /pub/Linux/kernel/patches/network/combinet1000isdn-1.02.tar.gz




  13.7.6.  More information:

  Harald Milz has put together a World Wide Web page for Linux ISDN
  support and it is available at Linux ISDN Web Page
  <http://www.ix.de/ix/linux/linux-isdn.html>.  A more generic site
  containing information about ISDN is available at Dan Kegel's ISDN
  home page <http://alumni.caltech.edu/~dank/isdn/>.


  13.8.  System-V Streams

  The LiS (Linux Streams) project has formed to develop and implement
  System-V Streams for Linux. They have a World Wide Web page at Linux
  Streams Web Page <http://www.uc3m.es/~LiS/> where the status of the
  project can be obtained and where you can locate contact information
  and test code.


  13.9.  ATM (Asynchronous Transfer Mode) support.

  Werner Almesberger has put together a World Wide site on the topic of
  Linux support for ATM. It is available at lrcwww.epfl.ch
  <http://lrcwww.epfl.ch/linux-atm/>.  There is experimental software
  which supports raw ATM connections and some basic IP over ATM
  available at the pre-alpha stage and this can be obtained from the Web
  Site. The site contains a good deal of interesting information on ATM.

  A mail list has been establised to discuss ATM for Linux and you can
  subscribe by sending a mail message with the body subscribe linux-atm
  to: [e-mail]


  13.10.  Appletalk support.

  If you have some Apple machines on your network that you'd like your
  linux machine to be able to share filesystems and printers with then
  the linux appletalk support is what you are after.

  The following information was supplied mostly by Cees de Groot
  <[e-mail] who compiled it from his own experience with
  assistance from Dana Basken <[e-mail]> and others on
  the net.


  13.10.1.  Building the kernel with Appletalk DDP support

  Alan Cox has developed some experimental and working support for the
  Apple Ethertalk specification. It is now a part of the later 1.2.*
  revision kernels and the new linux 1.3.* revision kernels so to build
  the kernel support for it you need only compile up a recent kernel,
  make sure you select the following configuration option:



       #
       # cd /usr/src/linux
       # make config
        ...
        ...
           Appletalk DDP ? y
        ...
        ...
       #



  13.10.2.  Building the Appletalk configuration tools and daemons.

  You will need some additional software as the kernel support only
  provides enough to do basic networking, none of the higher layer
  protocols are implented in the kernel.

  Wesley Craig <[e-mail] represents a team called the Research
  Systems Unix Group at the University of Michigan, and they have
  produced a package called netatalk which provides software that
  implements the Appletalk protocol stack and some useful utilities.

  You can obtain it from:

  University of Michigan
  <ftp://terminator.rs.itd.umich.edu/unix/netatalk/>

  you will need at least version 1.3.3b2 as earlier versions did not
  support Linux.

  To build and install that package something like:



       # cd /usr/src
       # tar xvfz .../netatalk
       - You may want to edit the `Makefile' at this point, specifically to change
         the DESTDIR variable which defines where the files will be installed later.
         Teh default of /usr/local/atalk is fairly safe.
       - You should then just have to make the software. My `uname' program wasn't
         in the /bin directory so I edited the Makefile to reflect this change too.
       # make
       - as root:
       # make install




  You should then end up with a whole range of new commands to play
  with.


  13.10.3.  Configuring the Appletalk software.

  The first thing you need to do to make it all work is add the contents
  of the services.atalk file to your /etc/services file, just append it
  to the end of the file.

  The next step is to create the appletalk configuration files in the
  /usr/local/atalk/etc directory (or whereever you installed the
  package).

  The first file to create is the /usr/local/atalk/etc/Atalkd.conf file.
  To start this file needs only one line that gives the name of the
  network device that support the network that your Apple machines are
  on:



       eth0




  The Appletalk daemon program will add extra details after it is run.


  13.10.4.  Exporting a Linux filesystems via Appletalk.

  You can export filesystems from your linux machine to the network so
  that Apple machine on the network can share them.

  To do this you must configure the
  /usr/local/atalk/etc/AppleVolumes.system file.

  Full details on how to do this and what the various options are can be
  found in the afpd man page.

  A sample would look like:



       /tmp Scratch
       /home/ftp/pub Public




  Which would export your /tmp filesystem as AppleShare Volume
  `Scratch', and your ftp public directory as AppleShare Volume
  `Public'.  The volume names are not mandatory, the daemon will choose
  some for you, but it won't hurt to specify them anyway.


  13.10.5.  Sharing your Linux printer across Appletalk.

  You can share your linux printer with your Apple machines quite
  simply.  You need to run the papd program which is the Appletalk
  Printer Access Protocol Daemon. When you run this program it will
  accept requests from your Apple machines and spool the print job to
  your local line printer daemon for printing.

  You need to edit the /usr/local/atalk/etc/papd.conf file to configure
  the daemon. The syntax of this file is the same as that of your usual
  /etc/printcap file. The name you give to the definition is registered
  with the Appletalk naming protocol, NBP.

  A sample configuration might look like:



       TricWriter:\
          :pr=lp:op=cg:




  Which would make a printer named `TricWriter' available to your
  Appletalk network, and all accepted jobs would be printed to the linux
  `lp' printer using lpd.


  13.10.6.  Starting the appletalk software.

  Ok, you should now be ready to test this basic configuration. There is
  an rc file supplied with the netatalk package that should work ok for
  you, so all you should have to do is:



       # /usr/local/atalk/etc/rc.atalk


  and all should startup and run ok. You should see no error messages
  and the software will send messages to the console indicating each
  stage as it starts.


  13.10.7.  Testing the appletalk software.

  To test that the software is functioning properly, go to one of your
  Apple machines, pull down the Apple menu, select the Chooser, click on
  AppleShare, and your Linux box should appear.


  13.10.8.  Caveats of the appletalk software.


  o  You may need to start the Appletalk support before you configure
     your IP network. If you have problems starting the Appletalk
     programs, or if after you start them you have trouble with your IP
     network, then try starting the Appletalk software before you run
     your /etc/rc.d/rc.inet1 file.

  o  The afpd (Apple Filing Protocol Daemon) severely messes up your
     hard disk. Below the mount points it creates a couple of
     directories: directory you access it will create a .AppleDouble
     below it so it can store resource forks, etc. So think twice before
     exporting /, you will have a great time cleaning up afterwards.

  o  The afpd program expects clear text passwords from the Macs.
     Security could be a problem, so be very careful when you run this
     daemon on a machine connected to the Internet, you have yourself to
     blame if somebody nasty does something bad.

  o  The existing diagnostic tools such as netstat and ifconfig don't
     support Appletalk. The raw information is available in the
     /proc/net/ directory if you need it.


  13.11.  IP_MASQUERADE - allow a number of hosts to pretend to be one.

  If you are one of the many people who have some sort of local network
  at home, whether it be a couple of machine connected via a
  slip/plip/ppp link to each other, or a number of machines connected to
  a private ethernet network who also has a dial-up Internet connection
  then you have probably at one time or another wanted the machines not
  directly connected to be able to communicate with the Internet. This
  is normally achieved by getting a valid register IP network address
  for your local network and asking your Internet Service Provider to
  kindly provide a network route to your network connection instead of
  the single host route they were previously providing. Unfortunately
  many Internet Service Providers will ask you to provide a good deal
  more dollars for the priveledge of better utilising the bandwidth of
  your connection and you probably don't much like that idea.

  IP_MASQUERADING provides a clever solution to this problem by making
  all of the machines on your network look like one very active
  networked machine.  It does this by performing real-time, on the fly
  address translations. Most of the code was authored by Pauline
  Middelink <[e-mail]>.

  Ken Eaves <[e-mail] provided most the information contained
  below and also provides the facilities to run the `masq' mailing list,
  so if you find the following helpful, thank Ken.




  13.11.1.  Obtaining the `masq' software.

  The IP_Masquerade software currently comes as a patch to the later
  linux 1.2.* series kernels and a new version of the ipfw command.  The
  ipfw program that comes with the net-tools software releases to
  configure it does not yet have the `masquerade' option built into it.
  The kernel you are using must support the ip_firewalling option for
  ip_masquerade to work.

  The patch file is available from:

  ftp.eves.com


       /pub/masq




  In this directory you will find patch files, new versions of the ipfw
  command and Ken's original Masquerade FAQ on which this text is based.

  The patch file is called masq-patch.1.2.n, so you must retrieve it.
  The files ipfw and ipfw-for-1.3.10 are for kernel version 1.2.* and
  1.3.10 respectively.


  13.11.2.  How do I install and compile the patch ?

  Assuming you have the source to a recent 1.2.* version kernel
  installed in the /usr/src/linux directory you would do the following:



       #
       # cd /usr/src
       # patch -p0 <.../masq-patch.1.2.n 2>patch.errs
       - check the patch.errs file for the string `fail'. If you can't find
         it then the patch applied successfully. If you can find it then something
         may have gone wrong double check that you have the correct version of
         kernel source.
       # cd /usr/src/linux
       # make config
       - You must answer `y' to:
         ...
         IP: forwarding/gatewaying (CONFIG_IP_FORWARD) [y]
         IP: firewalling (CONFIG_IP_FIREWALL) [y]
         IP: masquerading (ALPHA) [y]
         ...
       - The rest of the options you should answer as you normally would.
       # make dep
       # make clean
       - Build as you normally would, normally this would be:
       # make zlilo
       #




  After making sure that you are actually running your newly built
  kernel you need only ensure that you have a working copy of the ipfw
  program.  ipfw is normally installed in the /sbin so after testing the
  masquerade version you can simply copy it to /sbin/ipfw.  This is all
  that is necessary to get the kernel support installed.


  13.11.3.  How do I configure the IP_MASQUERADE software ?

  How you configure the IP_MASQUERADE function depends completely on how
  your network is built. The general idea is as follows: all of your
  local machine that you want to have access to the Internet must have
  their network default route pointing to your linux machine supporting
  IP_MASQUERADE.  Secondly, you must have an entry in the linux firewall
  table that says that your local machines should be masqueraded.

  To configure the IP-MASQUERADE function you use the ipfw command.  The
  ipfw command is normally used to configure the Linux firewall facility
  and because your masquerading host is acting as a firewall of sorts
  ipfw has been modified to take on this additional function.

  I'll present two example configurations that will probably cover most
  situations, if you have anything more complicated than these designs
  then you probably have the experience to work it out for yourself.

  Two machines connected to each other by slip or ppp:



        .-------.             .-------.
        |       |    slip     | linux |   slip/ppp
        | local |-----//------| masq  |-----//-------> To ISP
        |       |             | svr   |
        ._______.             ._______.

                ^            ^         ^
                |            |         |
           192.168.0.2   192.168.0.1  dynamically assigned





  Your /etc/rc.d/rc.inet1 file would have something like the following
  appended:



        ...
        ...
       # Allow machine 192.168.0.2 to be masqueraded to everybody
       ipfw a m all from 192.168.0.2/32 to 0.0.0.0/0
        ...
        ...




  Note the iii.iii.iii.iii/nn syntax. You might wonder what the /nn
  means and how you calculate it. This syntax is a means of encoding
  both an ip address and a netmask. What this syntax says is all
  addresses in which the first nn bits match those of iii.iii.iii.iii.
  The above example is for a single host, so all bits must match, since
  there are 32 bits in an IP address the syntax is /32.

  A private ethernet network of machines sharing a single internet link:







   .-------.    _
   |       | .2 |
   | local |----|
   |       |    | <-- Ethernet lan
   ._______.    |     192.168.0.0 netmask 255.255.255.0
                |
                |
   .-------.    |        .-------.
   |       | .3 |     .1 | linux |   slip/ppp
   | local |----|--------| masq  |-----//-------> To ISP
   |       |    |        | svr   |
   ._______.    -        ._______.

                                  ^
                                  |
                                 dynamically assigned




  For this configuration you have a single entry that describes the
  whole network, so you would use something like:



        ...
        ...
       # Allow all machines on network 192.168.0.0 to be masqueraded to everybody
       ipfw a m all from 192.168.0.2/24 to 0.0.0.0/0
        ...
        ...




  Again note the relationship between the netmask (255.255.255.0) and
  the ipfw syntax. A class C network (255.255.255.0) has 24 bits in its
  netmask.

  To make the job a little easier for you, here is a table of common
  network masks against matching bits:



       netmask             ipfw
       ---------------     ----
       255.0.0.0           /8
       255.255.0.0.0       /16
       255.255.255.0       /24
       255.255.255.128     /25
       255.255.255.192     /26
       255.255.255.224     /27
       255.255.255.240     /28
       255.255.255.248     /29
       255.255.255.255     /32





  13.11.4.  Where is IP_MASQUERADE being discussed ?

  There is a support mailing list at [e-mail].  To sign up email to
  [e-mail] and ask Ken to add you to the `masq' list. You can ask
  questions here or submit bug reports. When submitting bug reports
  please remember to include relevant details.
  13.12.  IPALIAS - multiple address per interface.

  If you are running a world wide web server and want to support
  multiple virtual servers, or your network support multiple subnets on
  the same piece of wire then you'll need to be able to have your
  machine respond to more than one address per interface.

  A facility called ipalias allows you to configure more than one
  address per interface.

  Robert Sanders <[e-mail]> has written linux support for
  this feature. It comes as a set of patches against linux kernel
  version 1.2.1.

  You can obtain it from:

  ftp.procyon.com


       /pub/linux/ipalias




  To install it you need the 1.2.1 kernel source installed and then:



       # cd /usr/src/linux
       # patch -p1 .../alias-patch-1.2.1-v1
       # make config
       # make dep; make clean; make zlilo




  You will also need to get the alias-net-tools.tar.gz file as it
  contains new versions of the ifconfig and netstat commands.


  13.12.1.  Configuring ip aliases.

  To configure an ip alias use the new ifconfig command as follows:



       # ifconfig eth0 alias 198.71.200.5




  This presumes that you already have the device configured to operate
  on your network and that you want 198.71.200.5 configured as a second
  address.


  14.  Diagnostic tools - How do I find out what is wrong?

  In this section I'll briefly describe some of the commonly used
  diagnostic tools that are available for your Linux network, and how
  you might use them to identify the cause of your network problems, or
  to teach yourself a bit more about how tcp/ip networking works. I'll
  gloss over some of the detail of how the tools work because this
  document is not an appropriate forum for describing that sort of
  detail, but I hope I'll have presented enough information that you'll
  have an understanding of how to use the tool, and to better understand
  the relevant man page or other documentation.


  14.1.  ping - are you there?

  The ping tool is located in the NetKit-B distribution as detailed
  above in the `Network Applications' section. ping, as the name
  implies, allows you to transmit a datagram at another host that it
  will reflect back at you if it is alive and working ok and the network
  in between is also ok. In its simplest form you would simply say:



       # ping gw
       PING gw.vk2ktj.ampr.org (44.136.8.97): 56 data bytes
       64 bytes from 44.136.8.97: icmp_seq=0 ttl=254 time=35.9 ms
       64 bytes from 44.136.8.97: icmp_seq=1 ttl=254 time=22.1 ms
       64 bytes from 44.136.8.97: icmp_seq=2 ttl=254 time=26.0 ms
       ^C

       --- gw.vk2ktj.ampr.org ping statistics ---
       3 packets transmitted, 3 packets received, 0% packet loss
       round-trip min/avg/max = 22.1/28.0/35.9 ms
       #




  What ping has done is resolved the hostname to an address, and using
  the icmp protocol has transmitted an icmp echo request datagram to the
  remote host periodically. For each echo request that the remote host
  receives it will formulate an icmp echo reply datagram which it will
  transmit back to you. Each line beginning with `64 bytes from ...'
  represents an echo reply received in response to an echo request. Each
  line tells you the address of the host that sent you the reply, the
  sequence number to which the reply was for, the time to live field and
  the total round trip time that was taken. The round trip time is the
  time between when the echo request datagram is transmitted, and the
  corresponding echo reply is received. This can be used as a measure of
  how fast or slow the network connection between the two machines is.

  The last two lines tell you how many datagrams were transmitted, how
  many valid responses were received and what percentage of the
  datagrams were lost. The percentage lost figure is a measure of how
  good or error free the network connection is. High percentage lost
  figures indicate such problems as a high error rate on a link
  somewhere between the hosts, exhausted capacity on a router or link
  somewhere, or high collision rate on an ethernet lan. You can use ping
  to identify where this problem might be by running ping sessions to
  each of the routed points that make up the network path. When you find
  that you can ping somewhere without any datagram loss, but pinging
  anywhere past there causes you packet loss, you can deduce that the
  problem lies somewhere between those two points.


  14.2.  traceroute - How do I get there?

  The traceroute tool is found in the NetKit-A distribution detailed
  earlier. traceroute is primarily used for testing and displaying the
  path that your network connection would take to a destination host.
  traceroute also uses the icmp protocol, but it uses a clever trick to
  get each point along the path to send it back a reply as it creeps its
  way along. Its trick is to manually manipulate the time to live field
  of the datagrams it transmits. The time to live field is a mechanism
  that ensures that rogue datagrams do not get caught in a routing loop.
  Each time a datagram passes through a router it decrements the time to
  live field by one. If the time to live reaches zero then that router
  or host sends an icmp time to live expired message back to the host
  who transmitted the datagram to let it know the datagram has expired.
  traceroute uses this mechanism by sending a series of udp datagrams
  with the time to live beginning set at one, and incrementing each step
  it takes. By recording the addresses from the icmp time to live
  expired replies it receives in response to the datagrams dying it can
  determine the path taken to get to the destination.  An example of its
  use would look something like:



       # traceroute minnie.vk1xwt.ampr.org
       traceroute to minnie.vk1xwt (44.136.7.129), 30 hops max, 40 byte packets
        1  gw (44.136.8.97)  51.618 ms  30.431 ms  34.396 ms
        2  gw.uts (44.136.8.68) 2017.322 ms  2060.121 ms 1997.793 ms
        3  minnie.vk1xwt (44.136.7.129) 2205.335 ms  2319.728 ms  2279.643 ms
       #




  The first column tells us how many hops away (what the ttl value was),
  the second column is the hostname and address that responded if it
  could be resolved or just its address if it could not. The third,
  fourth and fifth columns are the round trip time for three consecutive
  datagrams to that point.  This tells us that the first hop in the
  network route is via gw.vk2ktj, and the three figures following are
  the round trip times to that router. The next hop was via
  gw.uts.ampr.org, and minnie.vk1xwt.ampr.org is one hop further away.
  You can deduce information about the network route by looking at the
  difference in times between each step in the route. You can see that
  the round trip times to gw are fairly fast, it is an ethernet
  connected host. gw.uts is substantially slower to get to than gw, it
  is across a low speed radio link, so you have the ethernet time plus
  the radio link time added together.  minnie.vk1xwt is only slightly
  slower than gw.uts, they are connected via a high speed network.

  If you perform a traceroute and you see the string !N appear after the
  time figure, this indicates that your traceroute program received a
  network unreachable response. This message tells you that the host or
  router who sent you the message did not know how to route to the
  destination address. This normally indicates that there is a network
  link down somewhere.  The last address listed is as far as you get
  before you find the faulty link.

  Similarly if you see the string !H this indicates that a host
  unreachable message has been received. This might suggest that you got
  as far as the ethernet that the remote host is connected to, but the
  host itself is not responding or is faulty.


  14.3.  tcpdump - capturing and displaying network activity.

  Adam Caldwell <[e-mail]> has ported the tcpdump
  utlility to linux. tcpdump allows you to take traces of network
  activity by intercepting the datagrams on their way in and out of your
  machine. This is useful for diagnosing difficult to identify network
  problems.

  You can find the source and binaries at: 103mor2.cs.ohiou.edu
  <ftp://ftp.funet.fi/pub/OS/Linux/PEOPLE/Linus/net-
  source/tools/tcpdump-3.0.3.tar.gz>

  tcpdump decodes each of the datagrams that it intercepts and displays
  them in a slightly cryptic looking format in text. You would use
  tcpdump if you were trying to diagnose a problem like protocol errors,
  or strange disconnections, as it allows you to actually see what has
  happened on the network. To properly use tcpdump you would need some
  understanding of the protocols and how they work, but it is useful for
  simpler duties such as ensuring that datagrams are actually leaving
  your machine on the correct port if you are trying to diagnose routing
  problems and for seeing if you are receiving datagrams from remote
  destinations.

  A sample of tcpdump output looks like this:



       # tcpdump -i eth0
       tcpdump: listening on eth0
       13:51:36.168219 arp who-has gw.vk2ktj.ampr.org tell albert.vk2ktj.ampr.org
       13:51:36.193830 arp reply gw.vk2ktj.ampr.org is-at 2:60:8c:9c:ec:d4
       13:51:37.373561 albert.vk2ktj.ampr.org > gw.vk2ktj.ampr.org: icmp: echo request
       13:51:37.388036 gw.vk2ktj.ampr.org > albert.vk2ktj.ampr.org: icmp: echo reply
       13:51:38.383578 albert.vk2ktj.ampr.org > gw.vk2ktj.ampr.org: icmp: echo request
       13:51:38.400592 gw.vk2ktj.ampr.org > albert.vk2ktj.ampr.org: icmp: echo reply
       13:51:49.303196 albert.vk2ktj.ampr.org.1104 > gw.vk2ktj.ampr.org.telnet: S 700506986:700506986(0) win 512 <mss 1436>
       13:51:49.363933 albert.vk2ktj.ampr.org.1104 > gw.vk2ktj.ampr.org.telnet: . ack 1103372289 win 14261
       13:51:49.367328 gw.vk2ktj.ampr.org.telnet > albert.vk2ktj.ampr.org.1104: S 1103372288:1103372288(0) ack 700506987 win 2048 <mss 432>
       13:51:49.391800 albert.vk2ktj.ampr.org.1104 > gw.vk2ktj.ampr.org.telnet: . ack 134 win 14198
       13:51:49.394524 gw.vk2ktj.ampr.org.telnet > albert.vk2ktj.ampr.org.1104: P 1:134(133) ack 1 win 2048
       13:51:49.524930 albert.vk2ktj.ampr.org.1104 > gw.vk2ktj.ampr.org.telnet: P 1:28(27) ack 134 win 14335

        ..
       #




  When you start tcpdump without arguments it grabs the first (lowest
  numbered) network device that is not the loopback device. You can
  specify which device to monitor with a command line argument as shown
  above.  tcpdump then decodes each datagram transmitted or received and
  displays them, one line each, in a textual form. The first column is
  obviously the time the datagram was transmitted or received. The
  remainder of the line is then dependent on the type of datagram. The
  first two lines in the sample are what an arp request from
  albert.vk2ktj for gw.vk2ktj look like. The next four lines are two
  pings from albert.vk2ktj to gw.vk2ktj, note that tcpdump actually
  tells you the name of the icmp datagram transmitted or received. The
  greater-than (>) symbol tells you which way the datagram was
  transmitted, that is, from who, to who. It points from the sender, to
  the receiver. The remainder of the sample trace are the establishment
  of a telnet connection from albert.vk2ktj to gw.vk2ktj.

  The number or name at the end of each hostname tells you what socket
  number is being used. tcpdump looks in your /etc/services file to do
  this translation.

  tcpdump explodes each of the fields, and so you can see the values of
  the window and mss parameters in some of the datagrams.

  The man page documents all of the options available to you.

  Note for PPP users: The version of tcpdump that is currently available
  does not support the PPP suite of protocols. Al Longyear has produced
  a pair of patches to correct this, but these have not been built into
  a tcpdump distribution yet. The patch files are located in the same
  directory on sunsite.unc.edu as the tcpdump package.


  14.4.  icmpinfo - logs icmp messages received.

  ICMP then Internet Control Message Protocol conveys useful information
  about the health of your IP network. Often ICMP messages are received
  and acted on silently with you never knowing of their presence.
  icmpinfo is a tool that will allow you to view ICMP messages much like
  tcpdump does.  Laurent Demailly <[e-mail]> took the bsd ping
  source and modified it heavily.

  Version 1.10 is available from:

  hplyot.obspm.fr


       /net/icmpinfo-1.10.tar.gz




  Compilation is as simple as:



       # cd /usr/src
       # cd icmpinfo-1.10
       # gzip -dc icmpinfo-1.10.tar.gz | tar xvf -
       # make




  You must be SuperUser to run icmpinfo. icmpinfo can either decode to
  the tty it was called from or send its output to the syslog utility.

  To test out how it works, try running icmpinfo and starting a
  traceroute to a remote host. You will see the icmp messages that
  traceroute uses listed on the output.



  15.  Some Frequently Asked Questions, with brief Answers.

  Following are some questions and answers that are commonly asked.


  15.1.  General questions:



     I have only a dialin terminal access to a machine on the net, can I
        use
        this as a network connection ?"  Yes you can, take a look at
        TERM. TERM allows you you to run network connections over a
        normal terminal session. It requires some modifications to the
        network applications to work with it, but binaries and sources
        are available for the most common ones already. take a look at
        the TERM-HOWTO <http://sunsite.unc.edu/mdw/HOWTO/Term-
        HOWTO.html> for lots more information.


     When I telnet/ftp/rlogin to my machine it takes forever, why?
        You do not have your name resolver configured properly. Reread
        the section on /etc/resolv.conf. You must have at least a
        nameserver entry configured.


     I want to build my own standalone network, what addresses do I use
        ?
        RFC1597 has specifically reserved some IP addresses for private
        networks.  You should use these as they prevent anything nasty
        happening if you accidentally get connected to the Internet. The
        addresses reserved are:


          10.0.0.0        -   10.255.255.255
          172.16.0.0      -   172.31.255.255
          192.168.0.0     -   192.168.255.255




     Note, reserved network addresses are of classes A, B and C, so you
     are not restricted in your network design or size. Since you won't
     be connecting to the Internet it doesn't matter if you use the same
     address as some other group or network, just so long as the
     addresses you use are unique within your network.


     I want the machines on my local network to work via my dial-ip
        Internet connection, how do I do it?
        You have three options. They are as follows:

     o  Ask your Internet Service Provider to provide a network route to
        you instead of a host route. This is likely to be expensive but
        is the best performing and technical option.

     o  Set up your machine that supports your dial-up link as a `SOCKS'
        based firewall. This will inherently provide a proxy function
        where the outside world thinks it is your router machine doing
        the talking where in fact it is doing it on behalf of the
        machines on your network. Check the Firewall-HOWTO
        <http://sunsite.unc.edu/mdw/HOWTO/Firewall-HOWTO.html> for
        detailed information on how to do this. This will require the
        machines on your network to have client programs that support
        the SOCKS capability.

     o  Configure and run the IP-Masquerade software. This is probably
        the simplest way, as it is fairly straightforward to do and
        doesn't require special clients on your machines. This software
        very cleverly performs address translations that make the
        machines on your network look like they are the machine
        supporting your dial-up connection. There are some limitations
        to how well this will work, but it is much lighter-weight than
        running a full firewall gateway.


     If sunacm.swan.ac.uk is down, how do I get the files specified ?
        `sunacm' is mirrored on:

        ftp.Uni-Mainz.DE


          /pub/Linux/packages/Net2Debugged




     and/or:

     ftp.infomagic.com


     /pub/mirrors/linux/sunacm





     How do I know what version of kernel/net code I am running ?
        The network code and kernel now have synchronised version
        numbers, so try:

        uname -a

        or:

        cat /proc/version


     How do I change the message that telnet users are given at connect?
        The /etc/issue is the message that is given to normal getty
        users when they login. Some telnetd programs use a different
        file /etc/issue.net instead. So if you find that changing your
        issue file doesn't work, try changing the other.



  15.2.  Error messages:



     I keep getting the error `eth0: transmit timed out'. What does this
        mean?
        This usually means that your Ethernet cable is unplugged, or
        that the setup parameters for your card (I/O address, IRQ, etc.)
        are not set correctly.  Check the messages at boot time and make
        sure that your card is recognized with the correct Ethernet
        address. If it is, check that there is no conflict with any
        other hardware in your machine, eg you might have a soundblaster
        sharing the same IRQ or i/o control port.


     I get errors `check Ethernet cable' when using the network.
        You probably have your Ethernet card configured incorrectly.
        Double check the settings in /usr/src/linux/drivers/net/CONFIG.
        If this checks out ok, you may in fact have a cabling problem,
        check the cables are plugged in securely.



  15.3.  Routing questions:



     Why do I get the message `obselete route request' when I use the
        route command ?
        You are using a version of route that is older than your kernel.
        You should upgrade to a newer version of route. Refer to the
        "The network configuration tool suite" section of this document
        for information on where to obtain the tool set.


     Why do I get a `network unreachable' message when I try and net-
        work?
        This message means that yours, or some other, machine doesn't
        know how to route to the host that you are attempting to ping or
        connect to. If it occurs for all hosts that you try, then it is
        probable that you don't have your default route set up properly,
        reread the `routing' section.


     I can ping my server/gateway, but can't ping or connect to anyone
        remote.
        This is probably due to a routing problem. Reread the `routing'
        section in this document. If this looks ok, then make sure that
        the host you are attempting to connect to has a route to you. If
        you are a dialin user then this is a common cause of problems,
        ensure that your server is either running a routing program like
        gated or routed, or that it is `prox arping' for you, otherwise
        you will be able to get datagrams to the remote host, but it
        won't know how to return datagrams to you.



  15.4.  Using Linux with fileservers/NFS:



     How do I use my existing Novell fileserver with my Linux machine ?
        If you have the Novell NFS Daemon code then it is easy, just NFS
        mount the Novell volume that you wish to use. If you don't, and
        you are really desperate to be able to do this, and you have a
        spare pc machine laying about, you are in luck. You can run a
        program called Stan's Own Server on the spare PC. First,
        configure the pc as a novell workstation with maps to the
        directories you want to nfs mount, then run SOS, and export
        those drive maps.  SOS is available from
        spdcc.com:pub/sos/sossexe.zoo


     Files get corrupted when running NFS over a network.
        Certain vendors (Sun primarily) shipped many machines running
        NFS without UDP checksums. Great on ethernet, suicide otherwise.
        UDP checksums can be enabled on most file servers. Linux has it
        enabled by default from pl13 onwards - but both ends need to
        have it enabled...


     Why are my NFS files all read only ?
        The Linux NFS server defaults to read only. RTFM the `exports'
        and nfsd manual pages. With non Linux servers you may also need
        to alter /etc/exports



  15.5.  slip questions:



     What do I do if I don't know my slip servers address ?
        dip doesn't really need to know the address of your slip server
        for slip to function. The remote option was added as a
        convenience so that dip could automate the ifconfig and route
        commands for you. If you don't know, and cannot find out the
        address of your slip server then Peter D. Junger
        [e-mail] has suggested that he simply used
        his own address wherever a dip script called for a remote
        address. This is a small kludge but it works ok, as the server's
        address never actually appears in the slip headers anyway.


     `dip' only works for root. How do I make it work for others?
        dip needs to be setuid root to do some of the things it needs to
        do, such as modifying the routing table. Uri Blumenthal
        recommends the following:

     o  Create a new group called dip in your /etc/group file, and place
        each person who you want to allow dial out operation in it.

     o  Then when logged in as root, do the following:

        # chown root.dip /usr/bin/dip
        # chmod u=rx,g=x,o= /usr/bin/dip
        # chmod u+s /usr/bin/dip



     Dial-In users will be restricted in what they can do by what is
     contained in the /etc/diphosts file.


     I get `DIP: tty: set_disc(1): Invalid argument', why?
        This usually suggests that your kernel has not been compiled
        with slip support in it. Check that /proc/net/dev contains
        devices called sl0, sl1 etc. It could also mean that your
        version of dip is very old. You should upgrade to a newer
        version.


     When I ping a host I get `wrong data byte #17...', why?
        This generally means that you have your modem configured for
        XON/XOFF flow control. SLIP must have an eight bit clean line,
        so you cannot use XON/XOFF flow control. Hardware handshaking
        works better anyway, use it.


     With SLIP I can ping my server, and other hosts, but telnet or ftp
        don't
        work."  This is most likely caused by a disagreement on the use
        of header compression between your server and your machine.
        Double check that both ends either are, or are not, using
        compression. They must match.


     How can I hang up the phone line when I'm done using SLIP?
        If you use dip to dial out on the SLIP line, just `dip -k'
        should do the trick. If not, try to kill the dip process that is
        running. When dip dies it should hang up the call. To give it
        the best chance to clean up after itself, try killing the
        process in the following sequence: `kill <pid>', `kill -hup
        <pid>', and finally, if the dip process still refuses to die,
        try `kill -9 <pid>'. The same philosophy should be applied to
        all unix processes that you are attempting to kill.


     I see a lot of overrun errors on my slip port, why ?
        The older network tools incorrectly report number of packets
        compressed as the number of packets overrun. This has been
        corrected, and shouldn't occur of you are running the new
        version kernel and tools. If it still is it probably indicates
        that your machine isn't keeping up with the rate of data
        incoming. If you are not using 16550AFN UARTs then you should
        upgrade to them. 16450, or 8250 generate an interrupt for every
        character they receive and are therefore very reliant on the
        processor to be able to find time to stop what it is doing an
        collect the character from them to ensure none get lost. The
        16550AFN has a 16 character FIFO, and they only generate
        interrupts when the FIFO is nearly full, or when they have had
        character waiting, this means that less interrupts get generated
        for the same amount of data, and that less time is spent
        servicing your serial port. If you want to use multiple serial
        ports you should mandatorily upgrade to 16550AFN UARTs anyway.


     Can I use two slip interfaces ?
        Yes. If you have, for example, three machines which you would
        like to interconnect, then you most certainly could use two slip
        interfaces on one machine and connect each of the other machines
        to it. Simply configure the second interface as you did the
        first. NOTE that the second interface will require a different
        IP address to the first. You may need to play with the routing a
        bit to get it to do what you want, but it should work.


     I have a multiport i/o card, how do I use more than 4 slip ports ?
        The kernel slip comes with a default of a maximum of 4 slip
        devices configured, this is set in the
        /usr/src/linux/drivers/net/slip.h file.  To increase it, say to
        16, change the #define SL_NRUNIT to 16, in place of the 4 that
        will be there. You also need to edit
        /usr/src/linux/drivers/net/Space.c and add sections for sl4, sl5
        etc. You can copy the existing driver definition as a template
        to make it easier. You will need to recompile the kernel for the
        change to take effect.



  15.6.  PPP questions.

  You should refer to the PPP-HOWTO
  <http://sunsite.unc.edu/mdw/HOWTO/PPP-HOWTO.html> for a list of PPP
  questions and answers compiled by Al Longyear.


  16.  Quick Guide - SLIP Server

  Configuring your linux machine as a slip server is a deceptively
  simple thing to do. The actual process is simple, but there are a
  number of different aspects to the configuration and understanding how
  each of the stages interact with each other is what will help you
  diagnose any problems you experience.  Here are the steps that you
  must follow to configure your linux machine as a slip server:


  1. Assemble your hardware. Avoid IRQ and shared memory conflicts. Test
     each of the serial ports by connecting a dumb terminal to each of
     the ports and use a null modem cable and a comms program like
     minicom or seyon to talk to each. Make sure you can send and
     receive characters. If you intend running a number of serial ports
     then try to use a smart serial board or use 16550AFN UARTs. This
     will help ease some of the work of handling interrupts generated by
     the serial ports.

  2. Build your kernel, make sure it has networking configured, IP
     Forwarding enabled, and SLIP configured. Make sure you configure
     CSLIP if you wish to use it. Double check you have IP Forwarding
     enabled.

  3. Install your kernel. Test the kernel. Check the /proc/net/dev file
     and make sure that you have sl0 and other slip devices listed. If
     not then you have probably made some error in configuring your
     kernel, or you are not actually running your new kernel.

  4. Configure a getty on the serial port(s) that you wish to use for
     your incoming calls. You should refer to the Serial-HOWTO
     <http://sunsite.unc.edu/mdw/HOWTO/Serial-HOWTO.html> for a
     description of how to do this. Remember to configure your modem so
     that the DCD pin tracks received carrier, this is how your getty
     will detect an incoming call.

  5. Test the getty to make sure it works. It is important that you do
     this before you start worrying about the actual SLIP configuration.
     Try dialing into your system, you should get a login: prompt and be
     able to login normally.

  6. Decide how you want your server to allocate addresses. If you want
     your users to get the same address each time they call then you
     want a static server, if you want to minimise the number of
     addresses you use and don't care what address your users are
     allocated then you want a dynamic server.

  7. Decide how you are going to build the SLIP server, whether you are
     going to use sliplogin, dip or dslip. If you wish to use the
     sliplogin package then refer to the "Slip Server using Sliplogin"
     section. If you are going to use dip then refer to section "Slip
     Server using DIP". If you want to build your slip server using the
     dslip package then refer to section "Slip Server using dslip".
     Ensure you have the appropriate software, it is a recent version
     and compile the software if necessary.

  8. If the addresses you are allocating to you slip users are part of
     your ethernet network, then make sure you read the Proxy ARP
     section and configure a proxy arp for each address. You may do this
     in the /etc/sliplogin and /etc/sliplogout files if you are using
     the sliplogin package. If the addresses you are allocating are from
     a network seperate to your ethernet network then you can use either
     proxy arp or gated. If you use gated then refer to the "gated"
     section.

  9. Test your slip server.



  17.  Known Bugs.

  The Linux networking code is still an evolving thing. It still has
  bugs though they are becoming less frequently reported now. The Linux
  Networking News <http://iifeak.swan.ac.uk/NetNews.html> is a World
  Wide Web page maintained by Alan Cox which contains information on the
  status of the NET-3 networking code. You can obtain information on
  what is known and what isn't, by reading the
  /usr/src/linux/net/inet/README file that accompanies the kernel
  source, or by joining the linux-net channel.


  18.  Copyright Message.

  The NET-2-HOWTO is copyright by Terry Dawson and Matt Welsh. A
  verbatim copy of this document may be reproduced and distributed in
  any medium, physical or electronic without permission of the authors.
  Translations are similarly permitted without express permission if
  such translations include a notice stating who performed the
  translation, and that it is a translation.  Commercial redistribution
  is allowed and encouraged, however, the authors would like to be
  notified of any such distributions.

  Short quotes may be used without prior consent by the authors.
  Derivative works and partial distributions of the NET-2-HOWTO must
  include either a verbatim copy of this file, or make a verbatim copy
  of this file available.  If the latter is the case, a pointer to the
  verbatim copy must be stated at a clearly visible place.

  In short, we wish to promote dissemination of this information through
  as many channels as possible. However, we wish to retain copyright on
  this HOWTO document, and would like to be notified of any plans to
  redistribute it.  Further we desire that ALL information provided in
  this HOWTO be disseminated.

  If you have any questions relating to the conditions of this
  copyright, please contact Matt Welsh, the Linux HOWTO coordinator, at:
  [e-mail]


  19.  Miscellaneous, and Acknowledgements.

  There are so many people who have contributed comments and suggestions
  for this update that I have forgotten who you are. Thanks.

  Please, if you have any comments or suggestions then mail them to me.
  I'm fairly busy these days, so I might not get back to you straight
  away, but I will certainly consider any suggestion you have.

  The Linux networking code has come a long way, and it hasn't been an
  easy trip, but the developers, all of them, have done an excellent job
  in getting together something that is functional, versatile, flexible,
  and free for us to use. We all owe them a great debt of thanks. Linus,
  Ross, Fred, Alan, the Alpha/Beta testers, the tools developers, and
  those offering moral support have all contributed to the code as it is
  today.

  For those that have an itch they want to scratch, happy hacking, here
  it is.


  regards Terry Dawson, vk2ktj.

  <[e-mail]>, or <[e-mail]>