io Programmo 11/IOPROG_11.ISO/docs/ax25-h~1

Text File | 1997-06-30 | 130.0 KB | 3,342 lines

  Linux AX25-HOWTO, Amateur Radio.
  Terry Dawson, VK2KTJ, [e-mail]
  v1.4, 20 June 1997

  The Linux Operating System is perhaps the only operating system in the
  world that can boast native and standard support for the AX.25 packet
  radio protocol utilised by Amateur Radio Operators worldwide. This
  document aims to describe how to install and configure this support.

  1.  Introduction.

  This document was originally an appendix to the HAM-HOWTO, but grew
  too large to be reasonably managed in that fashion. This document
  describes how to install and configure the native AX.25, NetRom and
  Rose support for Linux. A few typical configurations are described
  that could be used as models to work from.

  The Linux implementation of the amateur radio protocols is very
  flexible.  To people relatively unfamiliar with the Linux operating
  system the configuration process may look daunting and complicated. It
  will take you a little time to come to understand how the whole thing
  fits together. You will find configuration very difficult if you have
  not properly prepared yourself by learning about Linux in general. You
  cannot expect to switch from some other environment to Linux without
  learning about Linux itself.

  1.1.  Changes from the previous version

  Additions:
          Added the section missing from the BayCom configuration section.
          Added 'hdlcdrv' to the list of modules needed to 'insmod' for BayCom.
          Added Rose Uplink and Downlink configuration - thanks Rick

  Corrections/Updates:
          Added kernel compile options into low level configuration section.
          Removed that nasty axctl error.
          Many small changes here and there to the BayCom and SoundModem sections.
          Hopefully I've unconfused the kernel/tools issue.
          Updated the home ftp site.

  ToDo:
          Fix up the SCC section, this is probably wrong.
          Expand on the programming section.
          Add some references to AX.25 and NetRom source documentation.

  1.2.  Other related documentation.

  There is a lot of related documentation. There are many documents that
  relate to Linux networking in more general ways and I strongly
  recommend you also read these as they will assist you in your efforts
  and provide you with stronger insight into other possible
  configurations.

  They are:

  The HAM-HOWTO <http://sunsite.unc.edu/LDP/HOWTO/HAM-HOWTO.html>,

  the NET-3-HOWTO <http://sunsite.unc.edu/LDP/HOWTO/NET-3-HOWTO.html>,

  the Ethernet-HOWTO <http://sunsite.unc.edu/LDP/HOWTO/Ethernet-
  HOWTO.html>,

  and:

  the Firewall-HOWTO <http://sunsite.unc.edu/LDP/HOWTO/Firewall-
  HOWTO.html>

  More general Linux information may be found by reference to other
  Linux HOWTO <http://sunsite.unc.edu/LDP/HOWTO/> documents.

  2.  Where to obtain new versions of this document.

  The best place to obtain the latest version of this document is from a
  Linux Documentation Project archive. The Linux Documentation Project
  runs a Web Server and this document appears there as The AX25-HOWTO
  <http://sunsite.unc.edu/LDP/HOWTO/AX25-HOWTO.html>. You can always
  contact me, but I pass new versions of the document directly to the
  LDP HOWTO coordinator, so if it isn't there then chances are I haven't
  finished it.

  3.  The Packet Radio Protocols and Linux.

  The AX.25 protocol offers both connected and connectionless modes of
  operation, and is used either by itself for point-point links, or to
  carry other protocols such as TCP/IP and NetRom.

  It is similar to X.25 level 2 in structure, with some extensions to
  make it more useful in the amateur radio environment.

  The NetRom protocol is an attempt at a full network protocol and uses
  AX.25 at its lowest layer as a datalink protocol. It provides a
  network layer that is an adapted form of AX.25. The NetRom protocol
  features dynamic routing and node aliases.

  The Rose protocol was conceived and first implemented by Tom Moulton
  W2VY and is an implementation of the X.25 packet layer protocol and is
  designed to operate with AX.25 as its datalink layer protocol. It too
  provides a network layer. Rose addresses take the form of 10 digit
  numbers. The first four digits are called the Data Network
  Identification Code (DNIC) and are taken from Appendix B of the CCITT
  X.121 recommendation. More information on the Rose protocol may be
  ontained from the RATS Web server <http://www.rats.org/>.

  Alan Cox developed some early kernel based AX.25 software support for
  Linux.  Jonathon Naylor <[e-mail]> has taken up ongoing
  development of the code, has added NetRom and Rose support and is now
  the developer of the AX.25 related kernel code. DAMA support was
  developed by Joerg, DL1BKE, [e-mail]. Baycom and
  SoundModem support were added by Thomas Sailer,
  <[e-mail]>. The AX.25 utility software is now maintained
  by me.

  The Linux code supports KISS based TNC's (Terminal Node Controllers),
  the Ottawa PI card, the Gracilis PacketTwin card and other Z8530 SCC
  based cards with the generic SCC driver and both the Parallel and
  Serial port Baycom modems. Thomas's new soundmodem driver supports
  Soundblaster and soundcards based on the Crystal chipset.

  The User programs contain a simple PMS (Personal Message System), a
  beacon facility, a line mode connect program, `listen' an example of
  how to capture all AX.25 frames at raw interface level and programs to
  configure the NetRom protocol. Included also are an AX.25 server style
  program to handle and despatch incoming AX.25 connections and a NetRom
  daemon which does most of the hard work for NetRom support.

  3.1.  How it all fits together.

  The Linux AX.25 implementation is a brand new implementation. While in
  many ways it may looks similar to NOS, or BPQ or other AX.25
  implementations, it is none of these and is not identical to any of
  them. The Linux AX.25 implementation is capable of being configured to
  behave almost identically to other implementations, but the
  configuration process is very different.

  To assist you in understanding how you need to think when configuring
  this section describes some of the structural features of the AX.25
  implementation and how it fits into the context of the overall Linux
  structure.

  Simplified Protocol Layering Diagram

       -----------------------------------------------
       | AF_AX25 | AF_NETROM |  AF_INET    | AF_ROSE |
       |=========|===========|=============|=========|
       |         |           |             |         |
       |         |           |    TCP/IP   |         |
       |         |           ----------    |         |
       |         |   NetRom           |    | Rose    |
       |         -------------------------------------
       |            AX.25                            |
       -----------------------------------------------

  This diagram simply illustrates that NetRom, Rose and TCP/IP all run
  directly on top of AX.25, but that each of these protocols is treated
  as a seperate protocol at the programming interface. The `AF_' names
  are simply the names given to the `Address Family' of each of these
  protocols when writing programs to use them. The important thing to
  note here is the implicit dependence on the configuration of your
  AX.25 devices before you can configure your NetRom, Rose or TCP/IP
  devices.

  Software module diagram on Linux Network Implementation

  ----------------------------------------------------------------------------
   User    | Programs  |   call        node    ||  Daemons | ax25d  mheardd
           |           |   pms         mheard  ||          | inetd  netromd
  ----------------------------------------------------------------------------
           | Sockets   | open(), close(), listen(), read(), write(), connect()
           |           |------------------------------------------------------
           |           |    AF_AX25   |  AF_NETROM  |   AF_ROSE   |  AF_INET
           |------------------------------------------------------------------
  Kernel   | Protocols |    AX.25     |   NetRom    |     Rose    | IP/TCP/UDP
           |------------------------------------------------------------------
           | Devices   |    ax0,ax1   |  nr0,nr1    | rose0,rose1 | eth0,ppp0
           |------------------------------------------------------------------
           | Drivers   |  Kiss   PI2   PacketTwin   SCC   BPQ     | slip ppp
           |           |      Soundmodem      Baycom              | ethernet
  ----------------------------------------------------------------------------
  Hardware | PI2 Card, PacketTwin Card, SCC card, Serial port, Ethernet Card
  ----------------------------------------------------------------------------

  This diagram is a little more general than the first. This diagram
  attempts to show the relationship between user applications, the ker¡
  nel and the hardware.  It also shows the relationship between the
  Socket application programming interface, the actual protocol modules,
  the kernel networking devices and the device drivers. Anything in this
  diagram is dependent on anything underneath it, and in general you
  must configure from the bottom of the diagram upwards.  So for exam¡
  ple, if you want to run the call program you must also configure the
  Hardware, then ensure that the kernel has the appropriate device
  driver, that you create the appropriate network device, that the ker¡
  nel includes the desired protocol that presents a programming inter¡
  face that the call program can use. I have attempted to lay out this
  document in roughly that order.

  4.  The AX.25/NetRom/Rose software components.

  The AX.25 software is comprised of three components, the kernel
  source, the network configuration tools and the utility programs.

  The version 2.0.xx Linux kernels include the AX.25, NetRom, Z8530 SCC,
  PI card and PacketTwin drivers by default. These have been
  significantly enhanced in the 2.1.* kernels. Unfortunately, the rest
  of the 2.1.*  kernels makes them fairly unstable at the moment and not
  a good choice for a production system. To solve this problem Jonathon
  Naylor has prepared a patch kit which will bring the amateur radio
  protocol support in a 2.0.28 kernel up to the standard of the 2.1.*
  kernels. This is very simple to apply, and provides a range of
  facilities not present in the standard kernel such as Rose support.

  4.1.  Finding the kernel, tools and utility packages.

  4.1.1.  The kernel source:

  The kernel source can be found in its usual place at:

  ftp.funet.fi

       /pub/Linux/PEOPLE/Linus/v2.0/linux-2.0.30.tar.gz

  The current version of Jonathons upgrade patch is available at:

  ftp.pspt.fi

       /pub/linux/ham/ax25/ax25-module-14b.tar.gz

  4.1.2.  The network tools:

  The latest alpha release of the standard Linux network tools support
  AX.25 and NetRom and can be found at:

  ftp.inka.de

  /pub/comp/Linux/networking/net-tools/net-tools-1.33.tar.gz

  The latest ipfwadm package can be found at:

  ftp.xos.nl

       /pub/linux/ipfwadm/

  4.1.3.  The AX25 utilities:

  There are two different families of AX25-utilities. One is for the
  2.0.* kernels and the other will work with either the 2.1.* kernels or
  the 2.0.*+moduleXX kernels. The ax25-utils version number indicate the
  oldest version of kernel that they will work with. Please choose a
  version of the ax25-utils appropriate to your kernel. The following
  are working combinations.  You must use one of the following
  combinations, any other combination will not work, or will not work
  well.

       Linux Kernel            AX25 Utility set
       ---------------------   -------------------------
       linux-2.0.29            ax25-uitls-2.0.12c.tar.gz
       linux-2.0.28+module12   ax25-utils-2.1.22b.tar.gz
       linux-2.0.30+module14   ax25-utils-2.1.42.tar.gz
       linux-2.1.22++          ax25-utils-2.1.22b.tar.gz
       linux-2.1.42++          ax25-utils-2.1.42.tar.gz

  The AX.25 utility programs can be found at:

  ftp.pspt.fi <ftp://ftp.pspt.fi/pub/linux/ham/ax25/>

  or at:

  sunsite.unc.edu <ftp://sunsite.unc.edu/pub/Linux/apps/ham/>

  5.  Installing the AX.25/NetRom/Rose software.

  To successfully install AX.25 support on your linux system you must
  configure and install an appropriate kernel and then install the AX.25
  utilities.

  5.1.  Compiling the kernel.

  If you are already familiar with the process of compiling the Linux
  Kernel then you can skip this section, just be sure to select the
  appropriate options when compiling the kernel. If you are not, then
  read on.

  The normal place for the kernel source to be unpacked to is the
  /usr/src directory into a subdirectory called linux.  To do this you
  should be logged in as root and execute a series of commands similar
  to the following:

       # mv linux linux.old
       # cd /usr/src
       # tar xvfz linux-2.0.30.tar.gz
       # tar xvfz /pub/net/ax25/ax25-module-14b.tar.gz
       # patch -p0 </usr/src/ax25-module-14b/ax25-2.0.30-2.1.42-5.diff
       # cd linux

  After you have unpacked the kernel source and applied the upgrade, you
  need to run the configuration script and choose the options that suit
  your hardware configuration and the options that you wish built into
  your kernel.  You do this by using the command:

       # make menuconfig

  You might also try:

       # make config

  I'm going to describe the full screen method (menuconfig) because it
  is easier to move around, but you use whichever you are most
  comfortable with.

  In either case you will be offered a range of options at which you
  must answer `Y' or `N'. (Note you may also answer `M' if you are using
  modules.  For the sake of simplicity I will assume you are not, please
  make appropriate modifications if you are).

  The options most relevant to an AX.25 configuration are:

  Code maturity level options  --->
      ...
      [*] Prompt for development and/or incomplete code/drivers
      ...
  General setup  --->
      ...
      [*] Networking support
      ...
  Networking options  --->
      ...
      [*] TCP/IP networking
      [?] IP: forwarding/gatewaying
      ...
      [?] IP: tunneling
      ...
      [?] IP: Allow large windows (not recommended if <16Mb of memory)
      ...
      [*] Amateur Radio AX.25 Level 2
      [?] Amateur Radio NET/ROM
      [?] Amateur Radio X.25 PLP (Rose)
      ...
  Network device support  --->
      [*] Network device support
      ...
      [*] Radio network interfaces
      [?] BAYCOM ser12 and par96 driver for AX.25
      [?] Soundcard modem driver for AX.25
      [?] Soundmodem support for Soundblaster and compatible cards
      [?] Soundmodem support for WSS and Crystal cards
      [?] Soundmodem support for 1200 baud AFSK modulation
      [?] Soundmodem support for 4800 baud HAPN-1 modulation
      [?] Soundmodem support for 9600 baud FSK G3RUH modulation
      [?] Serial port KISS driver for AX.25
      [?] BPQ Ethernet driver for AX.25
      [?] Gracilis PackeTwin support for AX.25
      [?] Ottawa PI and PI/2 support for AX.25
      [?] Z8530 SCC KISS emulation driver for AX.25
      ...

  The options I have flagged with a `*' are those that you must must
  answer `Y' to. The rest are dependent on what hardware you have and
  what other options you want to include. Some of these options are
  described in more detail later on, so if you don't know what you want
  yet, then read ahead and come back to this step later.

  After you have completed the kernel configuration you should be able
  to cleanly compile your new kernel:

       # make dep
       # make clean
       # make zImage

  maake sure you move your arch/i386/boot/zImage file wherever you want
  it and then edit your /etc/lilo.conf file and rerun lilo to ensure
  that you actually boot from it.

  5.1.1.  A word about Kernel modules

  I recommend that you don't compile any of the drivers as modules. In
  nearly all installations you gain nothing but additional complexity.
  Many people have problems trying to get the modularised components
  working, not because the software is faulty but because modules are
  more complicated to install and configure.

  If you've chosen to compile any of the components as modules, then
  you'll also need to use:

       # make modules
       # make modules_install

  to install your modules in the appropriate location.

  You will also need to add some entries into your /etc/conf.modules
  file that will ensure that the kerneld program knows how to handle the
  kernel modules. You should add/modify the following:

       alias net-pf-3     ax25
       alias net-pf-6     netrom
       alias net-pf-11    rose
       alias tty-ldisc-1  slip
       alias tty-ldisc-3  ppp
       alias tty-ldisc-5  mkiss
       alias bc0          baycom
       alias nr0          netrom
       alias pi0a         pi2
       alias pt0a         pt
       alias scc0         optoscc    (or one of the other scc drivers)
       alias sm0          soundmodem
       alias tunl0        newtunnel
       alias char-major-4 serial
       alias char-major-5 serial
       alias char-major-6 lp

  5.1.2.  What's new in 2.0.*+ModuleXX or 2.1.* Kernels ?

  The 2.1.* kernels have enhanced versions of nearly all of the
  protocols and drivers. The most significant of the enhancements are:

     modularised
        the protocols and drivers have all been modularised so that you
        can insmod and rmmod them whenever you wish. This reduces the
        kernel memory requirements for infrequently used modules and
        makes development and bug hunting much simpler. That being said,
        it also makes configuration slightly more difficult.

     All drivers are now network drivers
        all of the network devices such as Baycom, SCC, PI, Packettwin
        etc now present a normal network interface, that is they now
        look like the ethernet driver does, they no longer look like
        KISS TNC's. A new utility called net2kiss allows you to build a
        kiss interface to these devices if you wish.
     bug fixed
        there have been many bug fixes and new features added to the
        drivers and protocols. The Rose protocol is one important
        addition.

  5.2.  The network configuration tools.

  Now that you have compiled the kernel you should compile the new
  network configuration tools. These tools allow you to modify the
  configuration of network devices and to add routes to the routing
  table.

  The new alpha release of the standard net-tools package includes
  support for AX.25 and NetRom support. I've tested this and it seems to
  work well for me.

  5.2.1.  Building the standard net-tools release.

  Don't forget to read the Release file and follow any instructions
  there. The steps I used to compile the tools were:

       # cd /usr/src
       # tar xvfz net-tools-1.33.tar.gz
       # cd net-tools-1.33
       # make config

  At this stage you will be presented with a series of configuration
  questions, similar to the kernel configuration questions. Be sure to
  include support for all of the protocols and network devices types
  that you intend to use. If you do not know how to answer a particular
  question then answer `Y'.

  The tools will compile cleanly against the source after you remove the
  first line "usage und man page, info text von alexey" from the file
  arp.c.

  When the compilation is complete, you should use the:

       # make install

  command to install the programs in their proper place.

  If you wish to use the IP firewall facilities then you will need the
  latest firewall administration tool ipfwadm. This tool replaces the
  older ipfw tool which will not work with new kernels.

  I compiled the ipfwadm utility with the following commands:

  # cd /usr/src
  # tar xvfz ipfwadm-2.0beta2.tar.gz
  # cd ipfwadm-2.0beta2
  # make install
  # cp ipfwadm.8 /usr/man/man8
  # cp ipfw.4 /usr/man/man4

  5.3.  The AX.25 user and utility programs.

  After you have successfully compiled and booted your new kernel, you
  need to compile the user programs. To compile and install the user
  programs you should use a series of commands similar to the following:

       # cd /usr/src
       # tax xvfz ax25-utils-2.1.42.tar.gz
       # cd ax25-utils-2.1.42
       # make config
       # make
       # make install

  The files will be installed under the /usr directory by default in
  subdirectories: bin, sbin, etc and man.

  If this is a first time installation, that is you've never installed
  any ax25 utilities on your machine before you should also use the:

       # make installconf

  command to install some sample configuration files into the /etc/ax25/
  directory from which to work.

  If you get messages something like:

  gcc -Wall -Wstrict-prototypes -O2 -I../lib -c call.c
  call.c: In function `statline':
  call.c:268: warning: implicit declaration of function `attron'
  call.c:268: `A_REVERSE' undeclared (first use this function)
  call.c:268: (Each undeclared identifier is reported only once
  call.c:268: for each function it appears in.)

  then you should double check that you have the ncurses package
  properly installed on your system. The configuration script attempts
  to locate your ncurses packages in the common locations, but some
  installations have ncurses badly installed and it is unable to locate
  them.

  6.  A note on callsigns, addresses and things before we start.

  Each AX.25 and NetRom port on your system must have a callsign/ssid
  allocated to it. These are configured in the configuration files that
  will be described in detail later on.

  Some AX.25 implementations such as NOS and BPQ will allow you to
  configure the same callsign/ssid on each AX.25 and NetRom port. For
  somewhat complicated technical reasons Linux does not allow this. This
  isn't as big a problem in practise as it might seem.

  This means that there are things you should be aware of and take into
  consideration when doing your configurations.

  1. Each AX.25 and NetRom port must be configured with a unique
     callsign/ssid.

  2. TCP/IP will use the callsign/ssid of the AX.25 port it is being
     transmitted or received by, ie the one you configured for the AX.25
     interface in point 1.

  3. NetRom will use the callsign/ssid specified for it in its
     configuration file, but this callsign is only used when your NetRom
     is speaking to another NetRom, this is not the callsign/ssid that
     AX.25 users who wish to use your NetRom `node' will use. More on
     this later.

  4. Rose will, by default, use the callsign/ssid of the AX.25 port,
     unless the Rose callsign has been specifically set using the
     `rsparms' command.  If you set a callsign/ssid using the `rsparms'
     command then Rose will use this callsign/ssid on all ports.

  5. Other programs, such as the `ax25d' program can listen using any
     callsign/ssid that they wish and these may be duplicated across
     different ports.

  6. If you are careful with routing you can configure the same IP
     address on all ports if you wish.

  6.1.  What are all those T1, T2, N2 and things ?

  Not every AX.25 implementation is a TNC2. Linux uses nomenclature that
  differs in some respects from that you will be used to if your sole
  experience with packet is a TNC. The following table should help you
  interpret what each of the configurable items are, so that when you
  come across them later in this text you'll understand what they mean.

  -------------------------------------------------------------------
  Linux  | TAPR TNC | Description
  -------------------------------------------------------------------
  T1     | FRACK    | How long to wait before retransmitting an
         |          | unacknowledged frame.
  -------------------------------------------------------------------
  T2     | RESPTIME | The minimum amount of time to wait for another
         |          | frame to be received before transmitting
         |          | an acknowledgement.
  -------------------------------------------------------------------
  T3     | CHECK    | The period of time we wait between sending
         |          | a check that the link is still active.
  -------------------------------------------------------------------
  N2     | RETRY    | How many times to retransmit a frame before
         |          | assuming the connection has failed.
  -------------------------------------------------------------------
  Idle   |          | The period of time a connection can be idle
         |          | before we close it down.
  -------------------------------------------------------------------
  Window | MAXFRAME | The maximum number of unacknowledged
         |          | transmitted frames.
  -------------------------------------------------------------------

  6.2.  Run time configurable parameters

  The 2.1.* and 2.0.* +moduleXX kernels have a new feature that allows
  you to change many previously unchangable parameters at run time. If
  you take a careful look at the /proc/sys/net/ directory structure you
  will see many files with useful names that describe various parameters
  for the network configuration. The files in the /proc/sys/net/ax25/
  directory each represents one configured AX.25 port. The name of the
  file relates to the name of the port.

  The structure of the files in /proc/sys/net/ax25/<portname>/ is as
  follows:

  FileName              Meaning              Values                  Default
  ip_default_mode       IP Default Mode      0=DG 1=VC               0
  ax25_default_mode     AX.25 Default Mode   0=Normal 1=Extended     0
  backoff_type          Backoff              0=Linear 1=Exponential  1
  connect_mode          Connected Mode       0=No 1=Yes              1
  standard_window_size  Standard Window      1  <= N <= 7            2
  extended_window_size  Extended Window      1  <= N <= 63           32
  t1_timeout            T1 Timeout           1s <= N <= 30s          10s
  t2_timeout            T2 Timeout           1s <= N <= 20s          3s
  t3_timeout            T3 Timeout           0s <= N <= 3600s        300s
  idle_timeout          Idle Timeout         0m <= N                 20m
  maximum_retry_count   N2                   1  <= N <= 31           10
  maximum_packet_length AX.25 Frame Length   1  <= N <= 512          256

  In the table T1, T2 and T3 are given in seconds, and the Idle Timeout
  is given in minutes. But please note that the values used in the
  sysctl interface are given in internal units where the time in seconds
  is multiplied by 10, this allows resolution down to 1/10 of a second.
  With timers that are allowed to be zero, eg T3 and Idle, a zero value
  indicates that the timer is disabled.

  The structure of the files in /proc/sys/net/netrom/ is as follows:

  FileName                       Values                  Default
  default_path_quality                                   10
  link_fails_count                                       2
  network_ttl_initialiser                                16
  obsolescence_count_initialiser                         6
  routing_control                                        1
  transport_acknowledge_delay                            50
  transport_busy_delay                                   1800
  transport_maximum_tries                                3
  transport_requested_window_size                        4
  transport_timeout                                      1200

  The structure of the files in /proc/sys/net/rose/ is as follows:

  FileName                       Values                  Default
  acknowledge_hold_back_timeout                          50
  call_request_timeout                                   2000
  clear_request_timeout                                  1800
  link_fail_timeout                                      1200
  maximum_virtual_circuits                               50
  reset_request_timeout                                  1800
  restart_request_timeout                                1800
  routing_control                                        1
  window_size                                            3

  To set a parameter all you need to do is write the desired value to
  the file itself, for example to check and set the Rose window size
  you'd use something like:

       # cat /proc/sys/net/rose/window_size
       3
       # echo 4 >/proc/sys/net/rose/window_size
       # cat /proc/sys/net/rose/window_size
       4

  7.  Configuring an AX.25 port.

  Each of the AX.25 applications read a particular configuration file to
  obtain the parameters for the various AX.25 ports configured on your
  Linux machine.  For AX.25 ports the file that is read is the
  /etc/ax25/axport file.  You must have an entry in this file for each
  AX.25 port you want on your system.

  7.1.  Creating the AX.25 network device.

  The network device is what is listed when you use the `ifconfig'
  command. This is the object that the Linux kernel sends and receives
  network data from. Nearly always the network device has a physical
  port associated with it, but there are occasions where this isn't
  necessary. The network device does relate directly to a device driver.

  In the Linux AX.25 code there are a number of device drivers. The most
  common is probably the KISS driver, but others are the SCC driver(s),
  the Baycom driver and the SoundModem driver.
  Each of these device drivers will create a network device when it is
  started.

  7.1.1.  Creating a KISS device.

  Kernel Compile Options:

       General setup  --->
           [*] Networking support
       Network device support  --->
           [*] Network device support
           ...
           [*] Radio network interfaces
           [*] Serial port KISS driver for AX.25

  Probably the most common configuration will be for a KISS TNC on a
  serial port.  You will need to have the TNC preconfigured and
  connected to your serial port.  You can use a communications program
  like minicom or seyon to configure the TNC into kiss mode.

  To create a KISS device you use the kissattach program. In it simplest
  form you can use the kissattach program as follows:

       # /usr/sbin/kissattach /dev/ttyS0 radio
       # kissparms -p radio -t 100 -s 100 -r 25

  The kissattach command will create a KISS network device. These
  devices are called `ax[0-9]'. The first time you use the kissattach
  command it creates `ax0', the second time it creates `ax1' etc. Each
  KISS device has an associated serial port.

  The kissparms command allows you to set various KISS parameters on a
  KISS device.

  Specifically the example presented would create a KISS network device
  using the serial device `/dev/ttyS0' and the entry from the
  /etc/ax25/axports with a port name of `radio'. It then configures it
  with a txdelay and slottime of 100 milliseconds and a ppersist value
  of 25.

  Please refer to the man pages for more information.

  7.1.1.1.  Configuring for Dual Port TNC's

  The mkiss utility included in the ax25-utils distribution allows you
  to make use of both modems on a dual port TNC. Configuration is fairly
  simple. It works by taking a single serial device connected to a
  single multiport TNC and making it look like a number of devices each
  connected to a single port TNC. You do this before you do any of the
  AX.25 configuration. The devices that you then do the AX.25
  configuration on are pseudo-TTY interfaces, (/dev/ttyp*), and not the
  actual serial device. Pseudo-TTY devices create a kind of pipe through
  which programs designed to talk to tty devices can talk to other
  programs designed to talk to tty devices. Each pipe has a master and a
  slave end. The master end is generally called `/dev/ptyp*' and the
  slave ends are called `/dev/ttyp*'. There is a one to one relationship
  between masters and slaves, so /dev/ptyp0 is the master end of a pipe
  with /dev/ttyp0 as its slave. You must open the master end of a pipe
  before opening the slave end. mkiss exploits this mechanism to split a
  single serial device into seperate devices.

  Example: if you have a dual port tnc and it is connected to your
  /dev/ttyS0 serial device at 9600 bps, the command:

       # /usr/sbin/mkiss -s 9600 /dev/ttyS0 /dev/ptyp0 /dev/ptyp1
       # /usr/sbin/kissattach /dev/ttyp0 port1
       # /usr/sbin/kissattach /dev/ttyp1 port2

  would create two pseudo-tty devices that each look like a normal
  single port TNC. You would then treat /dev/ttyp0 and /dev/ttyp1 just
  as you would a conventional serial device with TNC connected. This
  means you'd then use the kissattach command as described above, on
  each of those, in the example for AX.25 ports called port1 and port2.
  You shouldn't use kissattach on the actual serial device as the mkiss
  program uses it.

  The mkiss command has a number of optional arguments that you may wish
  to use. They are summarised as follows:

     -c enables the addition of a one byte checksum to each KISS frame.
        This is not supported by most KISS implementation, it is
        supported by the G8BPG KISS rom.

     -s <speed>
        sets the speed of the serial port.

     -h enables hardware handshaking on the serial port, it is off by
        default. Most KISS implementation do not support this, but some
        do.

     -l enables logging of information to the syslog logfile.

  7.1.2.  Creating a Baycom device.

  Kernel Compile Options:

       Code maturity level options  --->
           [*] Prompt for development and/or incomplete code/drivers
       General setup  --->
           [*] Networking support
       Network device support  --->
           [*] Network device support
           ...
           [*] Radio network interfaces
           [*] BAYCOM ser12 and par96 driver for AX.25

  Thomas Sailer, <[e-mail]>, despite the popularly held
  belief that it would not work very well, has developed Linux support
  for Baycom modems. His driver supports the Ser12 serial port, Par96
  and the enhanced PicPar parallel port modems.  Further information
  about the modems themselves may be obtained from the Baycom Web site
  <http://www.baycom.de/>.

  Your first step should be to determine the i/o and addresses of the
  serial or parallel port(s) you have Baycom modem(s) connected to.
  When you have these you must configure the Baycom driver with them.

  The BayCom driver creates network devices called: bc0, bc1, bc2 etc.
  when it is configured.

  The sethdlc utility allows you to configure the driver with these
  parameters, or, if you have only one Baycom modem installed you may
  specify the parameters on the insmod commmand line when you load the
  Baycom module.

  For example, a simple configuration.  Disable the serial driver for
  COM1: then configure the Baycom driver for a Ser12 serial port modem
  on COM1: with the software DCD option enabled:

       # setserial /dev/ttyS0 uart none
       # insmod hdlcdrv
       # insmod baycom mode="ser12*" iobase=0x3f8 irq=4

  Par96 parallel port type modem on LPT1: using hardware DCD detection:

       # insmod hdlcdrv
       # insmod baycom mode="par96" iobase=0x378 irq=7 options=0

  This is not really the preferred way to do it. The sethdlc utility
  works just as easily with one device as with many.

  The sethdlc man page has the full details, but a couple of examples
  will illustrate the most important aspects of this configuration. The
  following examples assume you have already loaded the Baycom module
  using:

       # insmod hdlcdrv
       # insmod baycom

  or that you compiled the kernel with the driver inbuilt.

  Configure the bc0 device driver as a Parallel port Baycom modem on
  LPT1: with software DCD:

       # sethdlc -p -i bc0 mode par96 io 0x378 irq 7

  Configure the bc1 device driver as a Serial port Baycom modem on COM1:

  # sethdlc -p -i bc1 mode "ser12*" io 0x3f8 irq 4

  7.1.3.  Configuring the AX.25 channel access parameters.

  The AX.25 channel access parameters are the equivalent of the KISS
  ppersist, txdelay and slottime type parameters. Again you use the
  sethdlc utility for this.

  Again the sethdlc man page is the source of the most complete
  information but another example of two won't hurt:

  Configure the bc0 device with TxDelay of 200 mS, SlotTime of 100 mS,
  PPersist of 40 and half duplex:

       # sethdlc -i bc0 -a txd 200 slot 100 ppersist 40 half

  Note that the timing values are in milliseconds.

  7.1.3.1.  Configuring the Kernel AX.25 to use the BayCom device

  The BayCom driver creates standard network devices that the AX.25
  Kernel code can use. Configuration is much the same as that for a PI
  or PacketTwin card.

  The first step is to configure the device with an AX.25 callsign. The
  ifconfig utility may be used to perform this.

       # /sbin/ifconfig bc0 hw ax25 VK2KTJ-15 up

  will assign the BayCom device bc0 the AX.25 callsign VK2KTJ-15.
  Alternatively you can use the axparms command, you'll still need to
  use the ifconfig command to bring the device up though:

       # ifconfig bc0 up
       # axparms -setcall bc0 vk2ktj-15

  The next step is to create an entry in the /etc/ax25/axports file as
  you would for any other device. The entry in the axports file is
  associated with the network device you've configured by the callsign
  you configure. The entry in the axports file that has the callsign
  that you configured the BayCom device with is the one that will be
  used to refer to it.

  You may then treat the new AX.25 device as you would any other. You
  can configure it for TCP/IP, add it to ax25d and run NetRom or Rose
  over it as you please.

  7.1.4.  Creating a SoundModem device.

  Kernel Compile Options:

       Code maturity level options  --->
           [*] Prompt for development and/or incomplete code/drivers
       General setup  --->
           [*] Networking support
       Network device support  --->
           [*] Network device support
           ...
           [*] Radio network interfaces
           [*] Soundcard modem driver for AX.25
           [?] Soundmodem support for Soundblaster and compatible cards
           [?] Soundmodem support for WSS and Crystal cards
           [?] Soundmodem support for 1200 baud AFSK modulation
           [?] Soundmodem support for 4800 baud HAPN-1 modulation
           [?] Soundmodem support for 9600 baud FSK G3RUH modulation

  Thomas Sailer has built a new driver for the kernel that allows you to
  use your soundcard as a modem. Connect your radio directly to your
  soundcard to play packet! Thomas recommends at least a 486DX2/66 if
  you want to use this software as all of the digital signal processing
  is done by the main CPU.

  The driver currently emulates 1200 bps AFSK, 4800 HAPN and 9600 FSK
  (G3RUH compatible) modem types. The only sound cards currently
  supported are SoundBlaster and WindowsSoundSystem Compatible models.
  The sound cards require some circuitry to help them drive the Push-To-
  Talk circuitry, and information on this is available from Thomas's
  SoundModem PTT circuit web page
  <http://www.ife.ee.ethz.ch/~sailer/pcf/ptt_circ/ptt.html>. There are
  quite a few possible options, they are: detect the sound output from
  the soundcard, or use output from a parallel port, serial port or midi
  port. Circuit examples for each of these are on Thomas's site.

  The SoundModem driver creates network devices called: sm0, sm1, sm2
  etc when it is configured.

  Note: the SoundModem driver competes for the same resources as the
  Linux sound driver. So if you wish to use the SoundModem driver you
  must ensure that the Linux sound driver is not installed. You can of
  course compile them both as modules and insert and remove them as you
  wish.

  7.1.4.1.  Configuring the sound card.

  The SoundModem driver does not initialise the sound card. The
  ax25-utils package includes a utility to do this called `setcrystal'
  that may be used for SoundCards based on the Crystal chipset. If you
  have some other card then you will have to use some other software to
  initialise it.  Its syntax is fairly straightforward:

       setcrystal [-w wssio] [-s sbio] [-f synthio] [-i irq] [-d dma] [-c dma2]

  So, for example, if you wished to configure a soundblaster card at i/o
  base address 0x388, irq 10 and DMA 1 you would use:
       # setcrystal -s 0x388 -i 10 -d 1

  To configure a WindowSoundSystem card at i/o base address 0x534, irq
  5, DMA 3 you would use:

       # setcrystal -w 0x534 -i 5 -d 3

  The [-f synthio] parameter is the set the synthesiser address, and the
  [-c dma2] parameter is to set the second DMA channel to allow full
  duplex operation.

  7.1.4.2.  Configuring the SoundModem driver.

  When you have configured the soundcard you need to configure the
  driver telling it where the sound card is located and what sort of
  modem you wish it to emulate.

  The sethdlc utility allows you to configure the driver with these
  parameters, or, if you have only one soundcard installed you may
  specify the parameters on the insmod commmand line when you load the
  SoundModem module.

  For example, a simple configuration, with one SoundBlaster soundcard
  configured as described above emulating a 1200 bps modem:

       # insmod hdlcdrv
       # insmod soundmodem mode="sbc:afsk1200" iobase=0x220 irq=5 dma=1

  This is not really the preferred way to do it. The sethdlc utility
  works just as easily with one device as with many.

  The sethdlc man page has the full details, but a couple of examples
  will illustrate the most important aspects of this configuration. The
  following examples assume you have already loaded the SoundModem
  modules using:

       # insmod hdlcdrv
       # insmod soundmodem

  or that you compiled the kernel with the driver inbuilt.

  Configure the driver to support the WindowsSoundSystem card we
  configured above to emulate a G3RUH 9600 compatible modem as device
  sm0 using a parallel port at 0x378 to key the Push-To-Talk:

       # sethdlc -p -i sm0 mode wss:fsk9600 io 0x534 irq 5 dma 3 pario 0x378

  Configure the driver to support the SoundBlaster card we configured
  above to emulate a 4800 bps HAPN modem as device sm1 using the serial
  port located at 0x2f8 to key the Push-To-Talk:

       # sethdlc -p -i sm1 mode sbc:hapn4800 io 0x388 irq 10 dma 1 serio 0x2f8

  Configure the driver to support the SoundBlaster card we configured
  above to emulate a 1200 bps AFSK modem as device sm1 using the serial
  port located at 0x2f8 to key the Push-To-Talk:

       # sethdlc -p -i sm1 mode sbc:afsk1200 io 0x388 irq 10 dma 1 serio 0x2f8

  7.1.4.3.  Configuring the AX.25 channel access parameters.

  The AX.25 channel access parameters are the equivalent of the KISS
  ppersist, txdelay and slottime type parameters. You use the sethdlc
  utility for this as well.

  Again the sethdlc man page is the source of the most complete
  information but another example of two won't hurt:

  Configure the sm0 device with TxDelay of 100 mS, SlotTime of 50mS,
  PPersist of 128 and full duplex:

       # sethdlc -i sm0 -a txd 100 slot 50 ppersist 128 full

  Note that the timing values are in milliseconds.

  7.1.4.4.  Setting the audio levels and tuning the driver.

  It is very important that the audio levels be set correctly for any
  radio based modem to work. This is equally true of the SoundModem.
  Thomas has developed some utility programs that make this task easier.
  They are called smdiag and smmixer.

     smdiag
        provides two types of display, either an oscilloscope type
        display or an eye pattern type display.

     smmixer
        allows you to actually adjust the transmit and receive audio
        levels.

  To start the smdiag utility in 'eye' mode for the SoundModem device
  sm0 you would use:

       # smdiag -i sm0 -e

  To start the smmixer utility for the SoundModem device sm0 you would
  use:

       # smmixer -i sm0

  7.1.4.5.  Configuring the Kernel AX.25 to use the SoundModem

  The SoundModem driver creates standard network devices that the AX.25
  Kernel code can use. Configuration is much the same as that for a PI
  or PacketTwin card.

  The first step is to configure the device with an AX.25 callsign.  The
  ifconfig utility may be used to perform this.

       # /sbin/ifconfig sm0 hw ax25 VK2KTJ-15 up

  will assign the SoundModem device sm0 the AX.25 callsign VK2KTJ-15.
  Alternatively you can use the axparms command, but you still need the
  ifconfig utility to bring the device up:

       # ifconfig sm0 up
       # axparms -setcall sm0 vk2ktj-15

  The next step is to create an entry in the /etc/ax25/axports file as
  you would for any other device. The entry in the axports file is
  associated with the network device you've configured by the callsign
  you configure. The entry in the axports file that has the callsign
  that you configured the SoundModem device with is the one that will be
  used to refer to it.

  You may then treat the new AX.25 device as you would any other. You
  can configure it for TCP/IP, add it to ax25d and run NetRom or Rose
  over it as you please.

  7.1.5.  Creating a PI card device.

  Kernel Compile Options:

       General setup  --->
           [*] Networking support
       Network device support  --->
           [*] Network device support
           ...
           [*] Radio network interfaces
           [*] Ottawa PI and PI/2 support for AX.25

  The PI card device driver creates devices named `pi[0-9][ab]'. The
  first PI card detected will be allocated `pi0', the second `pi1' etc.
  The `a' and `b' refer to the first and second physical interface on
  the PI card. If you have built your kernel to include the PI card
  driver, and the card has been properly detected then you can use the
  following command to configure the network device:

       # /sbin/ifconfig pi0a hw ax25 VK2KTJ-15 up

  This command would configure the first port on the first PI card
  detected with the callsign VK2KTJ-15 and make it active. To use the
  device all you now need to do is to configure an entry into your
  /etc/ax25/axports file with a matching callsign/ssid and you will be
  ready to continue on.

  The PI card driver was written by David Perry, <[e-mail]>

  7.1.6.  Creating a PacketTwin device.

  Kernel Compile Options:

       General setup  --->
           [*] Networking support
       Network device support  --->
           [*] Network device support
           ...
           [*] Radio network interfaces
           [*] Gracilis PackeTwin support for AX.25

  The PacketTwin card device driver creates devices named `pt[0-9][ab]'.
  The first PacketTwin card detected will be allocated `pt0', the second
  `pt1' etc. The `a' and `b' refer to the first and second physical
  interface on the PacketTwin card. If you have built your kernel to
  include the PacketTwin card driver, and the card has been properly
  detected then you can use the following command to configure the
  network device:

       # /sbin/ifconfig pt0a hw ax25 VK2KTJ-15 up

  This command would configure the first port on the first PacketTwin
  card detected with the callsign VK2KTJ-15 and make it active. To use
  the device all you now need to do is to configure an entry into your
  /etc/ax25/axports file with a matching callsign/ssid and you will be
  ready to continue on.

  The PacketTwin card driver was written by Craig Small VK2XLZ,
  <[e-mail]>.

  7.1.7.  Creating a generic SCC device.

  Kernel Compile Options:

       General setup  --->
           [*] Networking support
       Network device support  --->
           [*] Network device support
           ...
           [*] Radio network interfaces
           [*] Z8530 SCC KISS emulation driver for AX.25

  Joerg Reuter, DL1BKE, [e-mail] has developed generic
  support for Z8530 SCC based cards. His driver is configurable to
  support a range of different types of cards and present an interface
  that looks like a KISS TNC so you can treat it as though it were a
  KISS TNC.

  7.1.7.1.  Obtaining and building the configuration tool package.

  While the kernel driver is included in the standard kernel
  distribution, Joerg distributes more recent versions of his driver
  with the suite of configuration tools that you will need to obtain as
  well.

  You can obtain the configuration tools package from:

  db0bm.automation.fh-aachen.de

       /incoming/dl1bke/

  or:

  insl1.etec.uni-karlsruhe.de

       /pub/hamradio/linux/z8530/

  or:

  ftp.ucsd.edu

       /hamradio/packet/tcpip/linux
       /hamradio/packet/tcpip/incoming/

  You will find multiple versions, choose the one that best suits the
  kernel you intend to use:

  z8530drv-2.4a.dl1bke.tar.gz   2.0.*
  z8530drv-utils-3.0.tar.gz    2.1.6 or greater

  The following command were what I used to compile and install the
  package for kernel version 2.0.25:

       # cd /usr/src
       # gzip -dc z8530drv-2.4a.dl1bke.tar.gz | tar xvpofz -
       # cd z8530drv
       # make clean
       # make dep
       # make module         # If you want to build the driver as a module
       # make for_kernel     # If you want the driver to built into your kernel
       # make install

  After the above is complete you should have three new programs
  installed in your /sbin directory: gencfg, sccinit and sccstat. It is
  these programs that you will use to configure the driver for your
  card.

  You will also have a group of new special device files created in your
  /dev called scc0 .. scc7. These will be used later and will be the
  `KISS' devices you will end up using.

  If you chose to 'make for_kernel' then you will need to recompile your
  kernel. To ensure that you include support for the z8530 driver you
  must be sure to answer `Y' to: `Z8530 SCC kiss emulation driver for
  AX.25' when asked during a kernel `make config'.

  If you chose to 'make module' then the new scc.o will have been
  installed in the appropriate /lib/modules directory and you do not
  need to recompile your kernel. Remember to use the insmod command to
  load the module before your try and configure it.

  7.1.7.2.  Configuring the driver for your card.

  The z8530 SCC driver has been designed to be as flexible as possible
  so as to support as many different types of cards as possible. With
  this flexibility has come some cost in configuration.

  There is more comprehensive documentation in the package and you
  should read this if you have any problems. You should particularly
  look at doc/scc_eng.doc or doc/scc_ger.doc for more detailed
  information. I've paraphrased the important details, but as a result
  there is a lot of lower level detail that I have not included.

  The main configuration file is read by the sccinit program and is
  called /etc/z8530drv.conf. This file is broken into two main stages:
  Configuration of the hardware parameters and channel configuration.
  After you have configured this file you need only add:

       # sccinit

  into the rc file that configures your network and the driver will be
  initialised according to the contents of the configuration file. You
  must do this before you attempt to use the driver.

  7.1.7.2.1.  Configuration of the hardware parameters.

  The first section is broken into stanzas, each stanza representing an
  8530 chip. Each stanza is a list of keywords with arguments. You may
  specify up to four SCC chips in this file by default. The #define
  MAXSCC 4 in scc.c can be increased if you require support for more.

  The allowable keywords and arguments are:

     chip
        the chip keyword is used to separate stanzas. It will take
        anything as an argument. The arguments are not used.

     data_a
        this keyword is used to specify the address of the data port for
        the z8530 channel `A'. The argument is a hexadecimal number e.g.
        0x300

     ctrl_a
        this keyword is used to specify the address of the control port
        for the z8530 channel `A'. The arguments is a hexadecimal number
        e.g. 0x304

     data_b
        this keyword is used to specify the address of the data port for
        the z8530 channel `B'. The argument is a hexadecimal number e.g.
        0x301

     ctrl_b
        this keyword is used to specify the address of the control port
        for the z8530 channel `B'. The arguments is a hexadecimal number
        e.g. 0x305

     irq
        this keyword is used to specify the IRQ used by the 8530 SCC
        described in this stanza. The argument is an integer e.g. 5

     pclock
        this keyword is used to specify the frequency of the clock at
        the PCLK pin of the 8530. The argument is an integer frequency
        in Hz which defaults to 4915200 if the keyword is not supplied.

     board
        the type of board supporting this 8530 SCC. The argument is a
        character string. The allowed values are:

        PA0HZP
           the PA0HZP SCC Card

        EAGLE
           the Eagle card

        PC100
           the DRSI PC100 SCC card

        PRIMUS
           the PRIMUS-PC (DG9BL) card

        BAYCOM
           BayCom (U)SCC card

     escc
        this keyword is optional and is used to enable support for the
        Extended SCC chips (ESCC) such as the 8580, 85180, or the 85280.
        The argument is a character string with allowed values of `yes'
        or `no'. The default is `no'.

     vector
        this keyword is optional and specifies the address of the vector
        latch (also known as "intack port") for PA0HZP cards. There can
        be only one vector latch for all chips. The default is 0.

     special
        this keyword is optional and specifies the address of the
        special function register on several cards. The default is 0.

     option
        this keyword is optional and defaults to 0.

  Some example configurations for the more popular cards are as follows:

     BayCom USCC

          chip    1
          data_a  0x300
          ctrl_a  0x304
          data_b  0x301
          ctrl_b  0x305
          irq     5
          board   BAYCOM
          #
          # SCC chip 2
          #
          chip    2
          data_a  0x302
          ctrl_a  0x306
          data_b  0x303
          ctrl_b  0x307
          board   BAYCOM

     PA0HZP SCC card

     chip 1
     data_a 0x153
     data_b 0x151
     ctrl_a 0x152
     ctrl_b 0x150
     irq 9
     pclock 4915200
     board PA0HZP
     vector 0x168
     escc no
     #
     #
     #
     chip 2
     data_a 0x157
     data_b 0x155
     ctrl_a 0x156
     ctrl_b 0x154
     irq 9
     pclock 4915200
     board PA0HZP
     vector 0x168
     escc no

     DRSI SCC card

          chip 1
          data_a 0x303
          data_b 0x301
          ctrl_a 0x302
          ctrl_b 0x300
          irq 7
          pclock 4915200
          board DRSI
          escc no

  If you already have a working configuration for your card under NOS,
  then you can use the gencfg command to convert the PE1CHL NOS driver
  commands into a form suitable for use in the z8530 driver
  configuration file.

  To use gencfg you simply invoke it with the same parameters as you
  used for the PE1CHL driver in NET/NOS. For example:

       # gencfg 2 0x150 4 2 0 1 0x168 9 4915200

  will generate a skeleton configuration for the OptoSCC card.

  7.1.7.3.  Channel Configuration

  The Channel Configuration section is where you specify all of the
  other parameters associated with the port you are configuring. Again
  this section is broken into stanzas. One stanza represents one logical
  port, and therefore there would be two of these for each one of the
  hardware parameters stanzas as each 8530 SCC supports two ports.

  These keywords and arguments are also written to the
  /etc/z8530drv.conf file and must appear after the hardware parameters
  section.

  Sequence is very important in this section, but if you stick with the
  suggested sequence it should work ok. The keywords and arguments are:

     device
        this keyword must be the first line of a port definition and
        specifies the name of the special device file that the rest of
        the configuration applies to. e.g. /dev/scc0

     speed
        this keyword specifies the speed in bits per second of the
        interface. The argument is an integer: e.g. 1200

     clock
        this keyword specifies where the clock for the data will be
        sourced. Allowable values are:

        dpll
           normal halfduplex operation

        external
           MODEM supplies its own Rx/Tx clock

        divider
           use fullduplex divider if installed.

     mode
        this keyword specifies the data coding to be used. Allowable
        arguments are: nrzi or nrz

     rxbuffers
        this keyword specifies the number of receive buffers to allocate
        memory for. The argument is an integer, e.g. 8.

     txbuffers
        this keyword specifies the number of transmit buffers to
        allocate memory for. The argument is an integer, e.g. 8.

     bufsize
        this keyword specifies the size of the receive and transmit
        buffers. The arguments is in bytes and represents the total
        length of the frame, so it must also take into account the AX.25
        headers and not just the length of the data field. This keyword
        is optional and default to 384

     txdelay
        the KISS transmit delay value, the argument is an integer in mS.

     persist
        the KISS persist value, the argument is an integer.

     slot
        the KISS slot time value, the argument is an integer in mS.

     tail
        the KISS transmit tail value, the argument is an integer in mS.

     fulldup
        the KISS full duplex flag, the argument is an integer.  1==Full
        Duplex, 0==Half Duplex.

     wait
        the KISS wait value, the argument is an integer in mS.

     min
        the KISS min value, the argument is an integer in S.

     maxkey
        the KISS maximum keyup time, the argument is an integer in S.

     idle
        the KISS idle timer value, the argument is an integer in S.

     maxdef
        the KISS maxdef value, the argument is an integer.

     group
        the KISS group value, the argument is an integer.

     txoff
        the KISS txoff value, the argument is an integer in mS.

     softdcd
        the KISS softdcd value, the argument is an integer.

     slip
        the KISS slip flag, the argument is an integer.

  7.1.7.4.  Using the driver.

  To use the driver you simply treat the /dev/scc* devices just as you
  would a serial tty device with a KISS TNC connected to it. For
  example, to configure Linux Kernel networking to use your SCC card you
  could use something like:

       # kissattach -s 4800 /dev/scc0 VK2KTJ

  You can also use NOS to attach to it in precisely the same way. From
  JNOS for example you would use something like:

       attach asy scc0 0 ax25 scc0 256 256 4800

  7.1.7.5.  The sccstat and sccparam tools.

  To assist in the diagnosis of problems you can use the sccstat program
  to display the current configuration of an SCC device. To use it try:

       # sccstat /dev/scc0

  you will displayed a very large amount of information relating to the
  configuration and health of the /dev/scc0 SCC port.
  The sccparam command allows you to change or modify a configuration
  after you have booted. Its syntax is very similar to the NOS param
  command, so to set the txtail setting of a device to 100mS you would
  use:

       # sccparam /dev/scc0 txtail 0x8

  7.1.8.  Creating a BPQ ethernet device.

  Kernel Compile Options:

       General setup  --->
           [*] Networking support
       Network device support  --->
           [*] Network device support
           ...
           [*] Radio network interfaces
           [*] BPQ Ethernet driver for AX.25

  Linux supports BPQ Ethernet compatibility. This enables you to run the
  AX.25 protocol over your Ethernet LAN and to interwork your linux
  machine with other BPQ machines on the LAN.

  The BPQ network devices are named `bpq[0-9]'. The `bpq0' device is
  associated with the `eth0' device, the `bpq1' device with the `eth1'
  device etc.

  Configuration is quite straightforward. You firstly must have
  configured a standard Ethernet device. This means you will have
  compiled your kernel to support your Ethernet card and tested that
  this works. Refer to the Ethernet-HOWTO <Ethernet-HOWTO.html> for more
  information on how to do this.

  To configure the BPQ support you need to configure the Ethernet device
  with an AX.25 callsign. The following command will do this for you:

       # /sbin/ifconfig bpq0 hw ax25 vk2ktj-14 up

  Again, remember that the callsign you specify should match the entry
  in the /etc/ax25/axports file that you wish to use for this port.

  7.1.9.  Configuring the BPQ Node to talk to the Linux AX.25 support.

  BPQ Ethernet normally uses a multicast address. The Linux
  implementation does not, and instead it uses the normal Ethernet
  broadcast address. The NET.CFG file for the BPQ ODI driver should
  therefore be modifified to look similar to this:

       LINK SUPPORT

               MAX STACKS 1
               MAX BOARDS 1

       LINK DRIVER E2000                    ; or other MLID to suit your card

               INT 10                       ;
               PORT 300                     ; to suit your card

               FRAME ETHERNET_II

               PROTOCOL BPQ 8FF ETHERNET_II ; required for BPQ - can change PID

       BPQPARAMS                            ; optional - only needed if you want
                                            ; to override the default target addr

               ETH_ADDR  FF:FF:FF:FF:FF:FF  ; Target address

  7.2.  Creating the /etc/ax25/axports file.

  The /etc/ax25/axports is a simple text file that you create with a
  text editor. The format of the /etc/ax25/axports file is as follows:

       portname  callsign  baudrate  paclen  window  description

  where:

     portname
        is a text name that you will refer to the port by.

     callsign
        is the AX.25 callsign you want to assign to the port.

     baudrate
        is the speed at which you wish the port to communicate with your
        TNC.

     paclen
        is the maximum packet length you want to configure the port to
        use for AX.25 connected mode connections.

     window
        is the AX.25 window (K) parameter. This is the same as the
        MAXFRAME setting of many tnc's.

     description
        is a textual description of the port.

  In my case, mine looks like:

       radio    VK2KTJ-15       4800        256     2       4800bps 144.800 MHz
       ether    VK2KTJ-14       10000000    256     2       BPQ/ethernet device

  Remember, you must assign unique callsign/ssid to each AX.25 port you
  create.  Create one entry for each AX.25 device you want to use, this
  includes KISS, Baycom, SCC, PI, PT and SoundModem ports. Each entry
  here will describe exactly one AX.25 network device. The entries in
  this file are associated with the network devices by the
  callsign/ssid. This is at least one good reason for requiring unique
  callsign/ssid.

  7.3.  Configuring AX.25 routing.

  You may wish to configure default digipeaters paths for specific
  hosts.  This is useful for both normal AX.25 connections and also IP
  based connections.  The axparms command enables you to do this. Again,
  the man page offers a complete description, but a simple example might
  be:

       # /usr/sbin/axparms -route add radio VK2XLZ VK2SUT

  This command would set a digipeater entry for VK2XLZ via VK2SUT on the
  AX.25 port named radio.

  8.  Configuring an AX.25 interface for TCP/IP.

  It is very simple to configure an AX.25 port to carry TCP/IP.  If you
  have KISS interfaces then there are two methods for configuring an IP
  address. The kissattach command has an option that allows you to do
  specify an IP address. The more conventional method using the ifconfig
  command will work on all interface types.

  So, modifying the previous KISS example:

       # /usr/sbin/kissattach -i 44.136.8.5 -m 512 /dev/ttyS0 radio
       # /sbin/route add -net 44.136.8.0 netmask 255.255.255.0 ax0
       # /sbin/route add default ax0

  to create the AX.25 interface with an IP address of 44.136.8.5 and an
  MTU of 512 bytes. You should still use the ifconfig to configure the
  other parameters if necessary.

  If you have any other interface type then you use the ifconfig program
  to configure the ip address and netmask details for the port and add a
  route via the port, just as you would for any other TCP/IP interface.
  The following example is for a PI card device, but would work equally
  well for any other AX.25 network device:

       # /sbin/ifconfig pi0a 44.136.8.5 netmask 255.255.255.0 up
       # /sbin/ifconfig pi0a broadcast 44.136.8.255 mtu 512
       # /sbin/route add -net 44.136.8.0 netmask 255.255.255.0 pi0a
       # /sbin/route add default pi0a

  The commands listed above are typical of the sort of configuration
  many of you would be familiar with if you have used NOS or any of its
  derivatives or any other TCP/IP software. Note that the default route
  might not be required in your configuration if you have some other
  network device configured.

  To test it out, try a ping or a telnet to a local host.

       # ping -i 5 44.136.8.58

  Note the use of the `-i 5' arguments to ping to tell it to send pings
  every 5 seconds instead of its default of 1 second.

  9.  Configuring a NetRom port.

  The NetRom protocol relies on, and uses the AX.25 ports you have
  created.  The NetRom protocol rides on top of the AX.25 protocol. To
  configure NetRom on an AX.25 interface you must configure two files.
  One file describes the Netrom interfaces, and the other file describes
  which of the AX.25 ports will carry NetRom. You can configure multiple
  NetRom ports, each with its own callsign and alias, the same procedure
  applies for each.

  9.1.  Configuring /etc/ax25/nrports

  The first is the /etc/ax25/nrports file. This file describes the
  NetRom ports in much the same way as the /etc/ax25/axports file
  describes the AX.25 ports. Each NetRom device you wish to create must
  have an entry in the /etc/ax25/nrports file. Normally a Linux machine
  would have only one NetRom device configured that would use a number
  of the AX.25 ports defined. In some situations you might wish a
  special service such as a BBS to have a seperate NetRom alias and so
  you would create more than one.

  This file is formatted as follows:

       name callsign  alias  paclen   description

  Where:

     name
        is the text name that you wish to refer to the port by.

     callsign
        is the callsign that the NetRom traffic from this port will use.
        Note, this is not that address that users should connect to to
        get access to a node style interface. (The node program is
        covered later). This callsign/ssid should be unique and should
        not appear elsewhere in either of the /etc/ax25/axports or the
        /etc/ax25/nrports files.

     alias
        is the NetRom alias this port will have assigned to it.

     paclen
        is the maximum size of NetRom frames transmitted by this port.

     description
        is a free text description of the port.

  An example would look something like the following:

       netrom  VK2KTJ-9        LINUX   236     Linux Switch Port

  This example creates a NetRom port known to the rest of the NetRom
  network as `LINUX:VK2KTJ-9'.

  This file is used by programs such as the call program.

  9.2.  Configuring /etc/ax25/nrbroadcast

  The second file is the /etc/ax25/nrbroadcast file. This file may
  contain a number of entries. There would normally be one entry for
  each AX.25 port that you wish to allow NetRom traffic on.

  This file is formatted as follows:

       axport min_obs def_qual worst_qual verbose

  Where:

     axport
        is the port name obtained from the /etc/ax25/axports file. If
        you do not have an entry in /etc/ax25/nrbroadcasts for a port
        then this means that no NetRom routing will occur and any
        received NetRom broadcasts will be ignored for that port.

     min_obs
        is the minimum obselesence value for the port.

     def_qual
        is the default quality for the port.

     worst_qual
        is the worst quality value for the port, any routes under this
        quality will be ignored.

     verbose
        is a flag determining whether full NetRom routing broadcasts
        will occur from this port or only a routing broadcast
        advertising the node itself.

  An example would look something like the following:

       radio    1       200      100         1

  9.3.  Creating the NetRom Network device

  When you have the two configuration files completed you must create
  the NetRom device in much the same way as you did for the AX.25
  devices.  This time you use the nrattach command. The nrattach works
  in just the same way as the axattach command except that it creates
  NetRom network devices called `nr[0-9]'. Again, the first time you use
  the nrattach command it creates the `nr0' device, the second time it
  creates the `nr1' network devices etc. To create the network device
  for the NetRom port we've defined we would use:

       # nrattach netrom

  This command would start the NetRom device (nr0) named netrom
  configured with the details specified in the /etc/ax25/nrports file.

  9.4.  Starting the NetRom daemon

  The Linux kernel does all of the NetRom protocol and switching, but
  does not manage some functions. The NetRom daemon manages the NetRom
  routing tables and generates the NetRom routing broadcasts. You start
  NetRom daemon with the command:

       # /usr/sbin/netromd -i

  You should soon see the /proc/net/nr_neigh file filling up with
  information about your NetRom neighbours.

  Remember to put the /usr/sbin/netromd command in your rc files so that
  it is started automatically each time you reboot.

  9.5.  Configuring NetRom routing.

  You may wish to configure static NetRom routes for specific hosts.
  The nrparms command enables you to do this. Again, the man page offers
  a complete description, but a simple example might be:

       # /usr/sbin/nrparms -nodes VK2XLZ-10 + #MINTO 120 5 radio VK2SUT-9

  This command would set a NetRom route to #MINTO:VK2XLZ-10 via a
  neighbour VK2SUT-9 on my AX.25 port called `radio'.

  You can manually create entries for new neighbours using the nrparms
  command as well. For example:

  # /usr/sbin/nrparms -routes radio VK2SUT-9 + 120

  This command would create VK2SUT-9 as a NetRom neighbour with a
  quality of 120 and this will be locked and will not be deleted
  automatically.

  10.  Configuring a NetRom interface for TCP/IP.

  Configuring a NetRom interface for TCP/IP is almost identical to
  configuring an AX.25 interface for TCP/IP.

  Again you can either specify the ip address and mtu on the nrattach
  command line, or use the ifconfig and route commands, but you need to
  manually add arp entries for hosts you wish to route to because there
  is no mechanism available for your machine to learn what NetRom
  address it should use to reach a particular IP host.

  So, to create an nr0 device with an IP address of 44.136.8.5, an mtu
  of 512 and configured with the details from the /etc/ax25/nrports file
  for a NetRom port named netrom you would use:

       # /usr/sbin/nrattach -i 44.136.8.5 -m 512 netrom
       # route add 44.136.8.5 nr0

  or you could use something like the following commands manually:

       # /usr/sbin/nrattach netrom
       # ifconfig nr0 44.136.8.5 netmask 255.255.255.0 hw netrom VK2KTJ-9
       # route add 44.136.8.5 nr0

  Then for each IP host you wish to reach via NetRom you need to set
  route and arp entries. To reach a destination host with an IP address
  of 44.136.80.4 at NetRom address BBS:VK3BBS via a NetRom neighbour
  with callsign VK2SUT-0 you would use commands as follows:

       # route add 44.136.80.4 nr0
       # arp -t netrom -s 44.136.80.4 vk2sut-0
       # nrparms -nodes vk3bbs + BBS 120 6 sl0 vk2sut-0

  The `120' and `6' arguments to the nrparms command are the NetRom
  quality and obsolescence count values for the route.

  11.  Configuring a Rose port.

  The Rose packet layer protocol is similar to layer three of the X.25
  specification. The kernel based Rose support is a modified version of
  the FPAC Rose implementation
  <http://fpac.lmi.ecp.fr/f1oat/f1oat.html>.

  The Rose packet layer protocol protocol relies on, and uses the AX.25
  ports you have created. The Rose protocol rides on top of the AX.25
  protocol.  To configure Rose you must create a configuration file that
  describes the Rose ports you want. You can create multiple Rose ports
  if you wish, the same procedure applies for each.

  11.1.  Configuring /etc/ax25/rsports

  The file where you configure your Rose interfaces is the
  /etc/ax25/rsports file. This file describes the Rose port in much the
  same way as the /etc/ax25/axports file describes the AX.25 ports.

  This file is formatted as follows:

       name  addresss  description

  Where:

     name
        is the text name that you wish to refer to the port by.

     address
        is the 10 digit Rose address you wish to assign to this port.

     description
        is a free text description of the port.

  An example would look something like the following:

       rose  5050294760  Rose Port

  Note that Rose will use the default callsign/ssid configured on each
  AX.25 port unless you specify otherwise.

  To configure a seperate callsign/ssid for Rose to use on each port you
  use the rsparms command as follows:

       # /usr/sbin/rsprams -call VK2KTJ-10

  This example would make Linux listen for and use the callsign/ssid
  VK2KTJ-10 on all of the configured AX.25 ports for Rose calls.

  11.2.  Creating the Rose Network device.

  When you have created the /etc/ax25/rsports file you may create the
  Rose device in much the same way as you did for the AX.25 devices.
  This time you use the rsattach command. The rsattach command creates
  network devices named `rose[0-5]'. The first time you use the rsattach
  command it create the `rose0' device, the second time it creates the
  `rose1' device etc. For example:

       # rsattach rose

  This command would start the Rose device (rose0) configured with the
  details specified in the /etc/ax25/rsports file for the entry named
  `rose'.

  11.3.  Configuring Rose Routing

  The Rose protocol currently supports only static routing. The rsparms
  utility allows you to configure your Rose routing table under Linux.

  For example:

       # rsparms -nodes add 5050295502 radio vk2xlz

  would add a route to Rose node 5050295502 via an AX.25 port named
  `radio' in your /etc/ax25/axports file to a neighbour with the call¡
  sign VK2XLZ.

  You may specify a route with a mask to capture a number of Rose
  destinations into a single routing entry. The syntax looks like:

       # rsparms -nodes add 5050295502/4 radio vk2xlz

  which would be identical to the previous example except that it would
  match any destination address that matched the first four digits sup¡
  plied, in this case any address commencing with the digits 5050. An
  alternate form for this command is:

       # rsparms -nodes add 5050/4 radio vk2xlz

  which is probably the less ambiguous form.

  12.  Making AX.25/NetRom/Rose calls.

  Now that you have all of your AX.25, NetRom and Rose interfaces
  configured and active, you should be able to make test calls.

  The AX25 Utilities package includes a program called `call' which is a
  splitscreen terminal program for AX.25, NetRom and Rose.

  A simple AX.25 call would look like:

       /usr/bin/call radio VK2DAY via VK2SUT

  A simple NetRom call to a node with an alias of SUNBBS would look
  like:

       /usr/bin/call netrom SUNBBS

  A simple Rose call to HEARD at node 5050882960 would look like:

       /usr/bin/call rose HEARD 5050882960

  Note: you must tell call which port you wish to make the call on, as
  the same destination node might be reachable on any of the ports you
  have configured.

  The call program is a linemode terminal program for making AX.25
  calls. It recognises lines that start with `~' as command lines.  The
  `~.' command will close the connection.

  Please refer to the man page in /usr/man for more information.

  13.  Configuring Linux to accept Packet connections.

  Linux is a powerful operating system and offers a great deal of
  flexibility in how it is configured. With this flexibility comes a
  cost in configuring it to do what you want. When configuring your
  Linux machine to accept incoming AX.25, NetRom or Rose connections
  there are a number of questions you need to ask yourself. The most
  important of which is: "What do I want users to see when they
  connect?". People are developing neat little applications that may be
  used to provide services to callers, a simple example is the pms
  program included in the AX25 utilities, a more complex example is the
  node program also included in the AX25 utilities. Alternatively you
  might want to give users a login prompt so that they can make use of a
  shell account, or you might even have written your own program, such
  as a customised database or a game, that you want people to connect
  to. Whatever you choose, you must tell the AX.25 software about this
  so that it knows what software to run when it accepts an incoming
  AX.25 connection.

  The ax25d program is similar to the inetd program commonly used to
  accept incoming TCP/IP connections on unix machines. It sits and
  listens for incoming connections, when it detects one it goes away and
  checks a configuration file to determine what program to run and
  connect to that connection. Since this the standard tool for accepting
  incoming AX.25, NetRom and Rose connections I'll describe how to
  configure it.

  13.1.  Creating the /etc/ax25/ax25d.conf file.

  This file is the configuration file for the ax25d AX.25 daemon which
  handles incoming AX.25, NetRom and Rose connections.

  The file is a little cryptic looking at first, but you'll soon
  discover it is very simple in practice, with a small trap for you to
  be wary of.

  The general format of the ax25d.conf file is as follows:

       # This is a comment and is ignored by the ax25d program.
       [port_name] || <port_name> || {port_name}
       <peer1>    window T1 T2 T3 idle N2 <mode> <uid> <cmd> <cmd-name> <arguments>
       <peer2>    window T1 T2 T3 idle N2 <mode> <uid> <cmd> <cmd-name> <arguments>
       parameters window T1 T2 T3 idle N2 <mode>
       <peer3>    window T1 T2 T3 idle N2 <mode> <uid> <cmd> <cmd-name> <arguments>
       default    window T1 T2 T3 idle N2 <mode> <uid> <cmd> <cmd-name> <arguments>

  Where:

     #  at the start of a line marks a comment and is completely ignored
        by the ax25d program.

     <port_name>
        is the name of the AX.25, NetRom or Rose port as specified in
        the /etc/ax25/axports, /etc/ax25/nrports and /etc/ax25/rsports
        files. The name of the port is surrounded by the `[]' brackets
        if it is an AX.25 port, the `<>' brackets if it is a NetRom
        port, or the `{}' brackets if it is a Rose port.  There is an
        alternate form for this field, and that is use prefix the port
        name with `callsign/ssid via' to indicate that you wish accept
        calls to the callsign/ssid via this interface. The example
        should more clearly illustrate this.

     <peer>
        is the callsign of the peer node that this particular
        configuration applies to. If you don't specify an SSID here then
        any SSID will match.

     window
        is the AX.25 Window parameter (K) or MAXFRAME parameter for this
        configuration.

     T1 is the Frame retransmission (T1) timer in half second units.

     T2 is the amount of time the AX.25 software will wait for another
        incoming frame before preparing a response in 1 second units.

     T3 is the amount of time of inactivity before the AX.25 software
        will disconnect the session in 1 second units.

     idle
        is the idle timer value in seconds.

     N2 is the number of consecutive retransmissions that will occur
        before the connection is closed.

     <mode>
        provides a mechanism for determining certain types of general
        permissions. The modes are enabled or disabled by supplying a
        combination of characters, each representing a permission. The
        characters may be in either upper or lower case and must be in a
        single block with no spaces.

        u/U
           UTMP                   - currently unsupported.

        v/V
           Validate call          - currently unsupported.

        q/Q
           Quiet                  - Don't log connection

        n/N
           check NetRom Neighbour - currently unsupported.

        d/D
           Disallow Digipeaters   - Connections must be direct, not
           digipeated.

        l/L
           Lockout                - Don't allow connection.

        */0
           marker                 - place marker, no mode set.

     <uid>
        is the userid that the program to be run to support the
        connection should be run as.

     <cmd>
        is the full pathname of the command to be run, with no arguments
        specified.

     <cmd-name>
        is the text that should appear in a ps as the command name
        running (normally the same as <cmd> except without the directory
        path information.

     <arguments>
        are the command line argument to be passed to the <:cmd> when it
        is run. You pass useful information into these arguments by use
        of the following tokens:

        %d Name of the port the connection was received on.

        %U AX.25 callsign of the connected party without the SSID, in
           uppercase.

        %u AX.25 callsign of the connected party without the SSID, in
           lowercase.

        %S AX.25 callsign of the connected party with the SSID, in
           uppercase.

        %s AX.25 callsign of the connected party with the SSID, in
           lowercase.

        %P AX.25 callsign of the remote node that the connection came in
           from without the SSID, in uppercase.

        %p AX.25 callsign of the remote node that the connection came in
           from without the SSID, in lowercase.

        %R AX.25 callsign of the remote node that the connection came in
           from with the SSID, in uppercase.
        %r AX.25 callsign of the remote node that the connection came in
           from with the SSID, in lowercase.

  You need one section in the above format for each AX.25, NetRom or
  Rose interface you want to accept incoming AX.25, NetRom or Rose
  connections on.

  There are two special lines in the paragraph, one starts with the
  string `parameters' and the other starts with the string `default'
  (yes there is a difference). These lines serve special functions.

  The `default' lines purpose should be obvious, this line acts as a
  catch-all, so that any incoming connection on the <interface_call>
  interface that doesn't have a specific rule will match the `default'
  rule. If you don't have a `default' rule, then any connections not
  matching any specific rule will be disconnected immediately without
  notice.

  The `parameters' line is a little more subtle, and here is the trap I
  mentioned earlier. In any of the fields for any definition for a peer
  you can use the `*' character to say `use the default value'. The
  `parameters' line is what sets those default values. The kernel
  software itself has some defaults which will be used if you don't
  specify any using the `parameters' entry. The trap is that the these
  defaults apply only to those rules below the `parameters' line not to
  those above. You may have more than one `parameters' rule per
  interface definition, and in this way you may create groups of default
  configurations.

  13.2.  A simple example ax25d.conf file.

  Ok, an illustrative example:

       # ax25d.conf for VK2KTJ - 02/03/97
       # This configuration uses the AX.25 port defined earlier.

       # <peer> Win T1  T2  T3  idl N2 <mode> <uid> <exec> <argv[0]>[<args....>]

       [VK2KTJ-0 via radio]
       parameters 1    10  *  *  *   *   *    root  /usr/sbin/axspawn axspawn %u +
       VK2XLZ     *     *  *  *  *   *   *
       VK2DAY     *     *  *  *  *   *   *
       NOCALL     *     *  *  *  *   *   L
       default    1    10  5 100 180 5   *    root  /usr/sbin/pms pms -a -o vk2ktj

       [VK2KTJ-1 via radio]
       default    *     *    *   *   *   0    root /usr/sbin/node node

       <netrom>
       parameters 1    10  *  *  *   *   *
       NOCALL     *     *  *  *  *   *   L
       default    *     *  *  *  *   *   0        root /usr/sbin/node node

       {VK2KTJ-0 via rose}
       parameters 1    10  *  *  *   *   *    root  /usr/sbin/axspawn axspawn %u +
       VK2XLZ     *     *  *  *  *   *   *
       VK2DAY     *     *  *  *  *   *   *
       NOCALL     *     *  *  *  *   *   L
       default    1    10  5 100 180 5   *    root  /usr/sbin/pms pms -a -o vk2ktj

       {VK2KTJ-1 via rose}
       default    *     *    *   *   *   0    root /usr/sbin/node node radio

  This example says that anybody attempting to connect to the callsign
  `VK2KTJ-0' heard on the AX.25 port called `radio' will have the
  following rules applied:

  Anyone whose callsign is set to `NOCALL' should be locked out, note
  the use of mode `L'.

  The parameters line changes two parameters from the kernel defaults
  (Window and T1) and will run the /usr/sbin/axspawn program for them.
  Any copies of /usr/sbin/axspawn run this way will appear as axspawn in
  a ps listing for convenience. The next two lines provide definitions
  for two stations who will receive those permissions.

  The last line in the paragraph is the `catch all' definition that
  everybody else will get (including VK2XLZ and VK2DAY using any other
  SSID other than -1).  This definition sets all of the parameters
  implicitly and will cause the pms program to be run with a command
  line argument indicating that it is being run for an AX.25 connection,
  and that the owner callsign is VK2KTJ. (See the `Configuring the PMS'
  section below for more details).

  The next configuration accepts calls to VK2KTJ-1 via the radio port.
  It runs the node program for everybody that connects to it.

  The next configuration is a NetRom configuration, note the use of the
  greater-then and less-than braces instead of the square brackets.
  These denote a NetRom configuration. This configuration is simpler, it
  simply says that anyone connecting to our NetRom port called `netrom'
  will have the node program run for them, unless they have a callsign
  of `NOCALL' in which case they will be locked out.

  The last two configurations are for incoming Rose connections. The
  first for people who have placed calls to `vk2ktj-0' and the second
  for `VK2KTJ-1 at the our Rose node address. These work precisely the
  same way. Not the use of the curly braces to distinguish the port as a
  Rose port.

  This example is a contrived one but I think it illustrates clearly the
  important features of the syntax of the configuration file. The
  configuration file is explained fully in the ax25d.conf man page. A
  more detailed example is included in the ax25-utils package that might
  be useful to you too.

  13.3.  Starting ax25d

  When you have the two configuration files completed you start ax25d
  with the command:

       # /usr/sbin/ax25d

  When this is run people should be able to make AX.25 connections to
  your Linux machine. Remember to put the ax25d command in your rc files
  so that it is started automatically when you reboot each time.

  14.  Configuring the node software.

  The node software was developed by Tomi Manninen
  <[e-mail]> and was based on the original PMS program.  It
  provides a fairly complete and flexible node capability that is easily
  configured. It allows users once they are connected to make Telnet,
  NetRom, Rose, and AX.25 connections out and to obtain various sorts of
  information such as Finger, Nodes and Heard lists etc. You can
  configure the node to execute any Linux command you wish fairly
  simply.

  The node would normally be invoked from the ax25d program although it
  is also capable of being invoked from the TCP/IP inetd program to
  allow users to telnet to your machine and obtain access to it, or by
  running it from the command line.

  14.1.  Creating the /etc/ax25/node.conf file.

  The node.conf file is where the main configuration of the node takes
  place. It is a simple text file and its format is as follows:

  # /etc/ax25/node.conf
  # configuration file for the node(8) program.
  #
  # Lines beginning with '#' are comments and are ignored.

  # Hostname
  # Specifies the hostname of the node machine
  hostname        radio.gw.vk2ktj.ampr.org

  # Local Network
  # allows you to specify what is consider 'local' for the
  # purposes of permission checking using nodes.perms.
  localnet        44.136.8.96/29

  # Hide Ports
  # If specified allows you to make ports invisible to users. The
  # listed ports will not be listed by the (P)orts command.
  hiddenports     rose netrom

  # Node Identification.
  # this will appear in the node prompt
  NodeId          LINUX:VK2KTJ-9

  # NetRom port
  # This is the name of the netrom port that will be used for
  # outgoing NetRom connections from the node.
  NrPort          netrom

  # Node Idle Timeout
  # Specifies the idle time for connections to this node in seconds.
  idletimout      1800

  # Connection Idle Timeout
  # Specifies the idle timer for connections made via this node in
  # seconds.
  conntimeout     1800

  # Reconnect
  # Specifies whether users should be reconnected to the node
  # when their remote connections disconnect, or whether they
  # should be disconnected complete.
  reconnect       on

  # Command Aliases
  # Provide a way of making complex node commands simple.
  alias           CONV    "telnet vk1xwt.ampr.org 3600"
  alias           BBS     "connect radio vk2xsb"

  # Externam Command Aliases
  # Provide a means of executing external commands under the node.
  # extcmd <cmdname> <flag> <userid> <command>
  # Flag == 1 is the only implemented function.
  # <command> is formatted as per ax25d.conf
  extcmd          PMS     1       root    /usr/sbin/pms pms -u %U -o VK2KTJ

  # Logging
  # Set logging to the system log. 3 is the noisiest, 0 is disabled.
  loglevel        3

  # The escape character
  # 20 = (Control-T)
  EscapeChar      20

  14.2.  Creating the /etc/ax25/node.perms file.

  The node allows you to assign permissions to users. These permissions
  allow you to determine which users should be allowed to make use of
  options such as the (T)elnet, and (C)onnect commands, for example, and
  which shouldn't. The node.perms file is where this information is
  stored and contains five key fields. For all fields an asterisk `*'
  character matches anything. This is useful for building default rules.

     user
        The first field is the callsign or user to which the permissions
        should apply.  Any SSID value is ignored, so you should just
        place the base callsign here.

     method
        Each protocol or access method is also given permissions. For
        example you might allow users who have connected via AX.25 or
        NetRom to use the (C)onnect option, but prevent others, such as
        those who are telnet connected from a non-local node from having
        access to it. The second field therefore allows you to select
        which access method this permissions rule should apply to.  The
        access methods allowed are:

          method  description
          ------  -----------------------------------------------------------
          ampr    User is telnet connected from an amprnet address (44.0.0.0)
          ax25    User connected by AX.25
          host    User started node from command line
          inet    user is telnet connected from a non-loca, non-ampr address.
          local   User is telnet connected from a 'local' host
          netrom  User connected by NetRom
          rose    User connected by Rose
          *       User connected by any means.

     port
        For AX.25 users you can control permissions on a port by port
        basis too if you choose. This allows you to determine what AX.25
        are allowed to do based on which of your ports they have
        connected to. The third field contains the port name if you are
        using this facility. This is useful only for AX.25 connections.

     password
        You may optionally configure the node so that it prompts users
        to enter a password when they connect. This might be useful to
        help protect specially configured users who have high authority
        levels. If the fourth field is set then its value will be the
        password that will be accepted.

     permissions
        The permissions field is the final field in each entry in the
        file.  The permissions field is coded as a bit field, with each
        facility having a bit value which if set allows the option to be
        used and if not set prevents the facility being used. The list
        of controllable facilities and their corresponding bit values
        are:

     value   description
     -----   -------------------------------------------------
      1      Login allowed.
      2      AX25 (C)onnects allowed.
      4      NetRom (C)onnects allowed.
      8      (T)elnet to local hosts allowed.
      16     (T)elnet to amprnet (44.0.0.0) hosts allowed.
      32     (T)elnet to non-local, non-amprnet hosts allowed.
      64     Hidden ports allowed for AX.25 (C)onnects.
      128    Rose (C)onnects allowed.

     To code the permissions value for a rule, simply take each of the
     permissions you want that user to have and add their values
     together. The resulting number is what you place in field five.

  A sample nodes.perms might look like:

       # /etc/ax25/node.perms
       #
       # The node operator is VK2KTJ, has a password of 'secret' and
       # is allowed all permissions by all connection methods
       vk2ktj  *       *       secret  255

       # The following users are banned from connecting
       NOCALL  *       *       *       0
       PK232   *       *       *       0
       PMS     *       *       *       0

       # INET users are banned from connecting.
       *       inet    *       *       0

       # AX.25, NetRom, Local, Host and AMPR users may (C)onnect and (T)elnet
       # to local and ampr hosts but not to other IP addresses.
       *       ax25    *       *       159
       *       netrom  *       *       159
       *       local   *       *       159
       *       host    *       *       159
       *       ampr    *       *       159

  14.3.  Configuring node to run from ax25d

  The node program would normally be run by the ax25d program.  To do
  this you need to add appropriate rules to the /etc/ax25/ax25d.conf
  file. In my configuration I wanted users to have a choice of either
  connecting to the node or connecting to other services. ax25d allows
  you to do this by cleverly creating creating port aliases. For
  example, given the ax25d configuration presented above, I want to
  configure node so that all users who connect to VK2KTJ-1 are given the
  node. To do this I add the following to my /etc/ax25/ax25d.conf file:

       [vk2ktj-1 via radio]
       default    *     *    *   *   *   0    root /usr/sbin/node node

  This says that the Linux kernel code will answer any connection
  requests for the callsign `VK2KTJ-1' heard on the AX.25 port named
  `radio', and will cause the node program to be run.

  14.4.  Configuring node to run from inetd

  If you want users to be able to telnet a port on your machine and
  obtain access to the node you can go this fairly easily. The first
  thing to decide is what port users should connect to. In this example
  I've arbitrarily chosen port 4000, though Tomi gives details on how
  you could replace the normal telnet daemon with the node in his
  documentation.

  You need to modify two files.

  To /etc/services you should add:

       node    3694/tcp        #OH2BNS's node software

  and to /etc/inetd.conf you should add:

       node    stream  tcp     nowait  root    /usr/sbin/node node

  When this is done, and you have restarted the inetd program any user
  who telnet connects to port 3694 of your machine will be prompted to
  login and if configured, their password and then they will be con¡
  nected to the node.

  15.  Configuring axspawn.

  The axspawn program is a simple program that allows AX.25 stations who
  connect to be logged in to your machine. It may be invoked from the
  ax25d program as described above in a manner similar to the node
  program. To allow a user to log in to your machine you should add a
  line similar to the following into your /etc/ax25/ax25d.conf file:

       default * * * * * 1 root /usr/sbin/axspawn axspawn %u

  If the line ends in the + character then the connecting user must hit
  return before they will be allowed to login. The default is to not
  wait.  Any individual host configurations that follow this line will
  have the axspawn program run when they connect. When axspawn is run it
  first checks that the command line argument it is supplied is a legal
  callsign, strips the SSID, then it checks that /etc/passwd file to see
  if that user has an account configured. If there is an account, and
  the password is either "" (null) or + then the user is logged in, if
  there is anything in the password field the user is prompted to enter
  a password. If there is not an existing account in the /etc/passwd
  file then axspawn may be configured to automatically create one.

  15.1.  Creating the /etc/ax25/axspawn.conf file.

  You can alter the behaviour of axspawn in various ways by use of the
  /etc/ax25/axspawn.conf file. This file is formatted as follows:

       # /etc/ax25/axspawn.conf
       #
       # allow automatic creation of user accounts
       create    yes
       #
       # guest user if above is 'no' or everything else fails. Disable with "no"
       guest     no
       #
       # group id or name for autoaccount
       group     ax25
       #
       # first user id to use
       first_uid 2001
       #
       # maximum user id
       max_uid   3000
       #
       # where to add the home directory for the new users
       home      /home/ax25
       #
       # user shell
       shell     /bin/bash
       #
       # bind user id to callsign for outgoing connects.
       associate yes

  The eight configurable characteristics of axspawn are as follows:

     #  indicates a comment.

     create
        if this field is set to yes then axspawn will attempt to
        automatically create a user account for any user who connects
        and does not already have an entry in the /etc/passwd file.

     guest
        this field names the login name of the account that will be used
        for people who connect who do not already have accounts if
        create is set to no. This is usually ax25 or guest.

     group
        this field names the group name that will be used for any users
        who connect and do not already have an entry in the /etc/passwd
        file.

     first_uid
        this is the number of the first userid that will be
        automatically created for new users.

     max_uid
        this is the maximum number that will be used for the userid of
        new users.

     home
        this is the home (login) directory of new users.

     shell
        this is the login shell of any new users.

     associate
        this flag indicates whether outgoing AX.25 connections made by
        this user after they login will use their own callsign, or your
        stations callsign.

  16.  Configuring the pms

  The pms program is an implementation of a simple personal message
  system. It was originally written by Alan Cox. Dave Brown, N2RJT,
  <[e-mail]> has taken on further development of it.  At present
  it is still very simple, supporting only the ability to send mail to
  the owner of the system and to obtain some limited system information
  but Dave is working to expand its capability to make it more useful.

  After that is done there are a couple of simple files that you should
  create that give users some information about the system and then you
  need to add appropriate entries into the ax25d.conf file so that
  connected users are presented with the PMS.

  16.1.  Create the /etc/ax25/pms.motd file.

  The /etc/ax25/pms.motd file contains the `message of the day' that
  users will be presented with after they connect and receive the usual
  BBS id header. The file is a simple text file, any text you include in
  this file will be sent to users.

  16.2.  Create the /etc/ax25/pms.info file.

  The /etc/ax25/pms.info file is also a simple text file in which you
  would put more detailed information about your station or
  configuration.  This file is presented to users in response to their
  issuing of the Info command from the PMS> prompt.

  16.3.  Associate AX.25 callsigns with system users.

  When a connected user sends mail to an AX.25 callsign, the pms expects
  that callsign to be mapped, or associated with a real system user on
  your machine. This is described in a section of its own.

  16.4.  Add the PMS to the /etc/ax25/ax25d.conf file.

  Adding the pms to your ax25d.conf file is very simple.  There is one
  small thing you need to think about though. Dave has added command
  line arguments to the PMS to allow it to handle a number of different
  text end-of-line conventions. AX.25 and NetRom by convention expect
  the end-of-line to be carriage return, linefeed while the standard
  unix end-of-line is just newline. So, for example, if you wanted to
  add an entry that meant that the default action for a connection
  received on an AX.25 port is to start the PMS then you would add a
  line that looked something like:

       default  1  10 5 100 5   0    root  /usr/sbin/pms pms -a -o vk2ktj

  This simply runs the pms program, telling it that it is an AX.25
  connection it is connected to and that the PMS owner is vk2ktj.  Check
  the man page for what you should specify for other connection methods.

  16.5.  Test the PMS.

  To test the PMS, you can try the following command from the command
  line:

  # /usr/sbin/pms -u vk2ktj -o vk2ktj

  Substitute your own callsign for mine and this will run the pms,
  telling it that it is to use the unix end-of-line convention, and that
  user logging in is vk2ktj. You can do all the things connected users
  can.

  Additionally you might try getting some other node to connect to you
  to confirm that your ax25d.conf configuration works.

  17.  Configuring the user_call programs.

  The `user_call' programs are really called: ax25_call and netrom_call.
  They are very simple programs designed to be called from ax25d to
  automate network connections to remote hosts. They may of course be
  called from a number of other places such as shell scripts or other
  daemons such as the node program.

  They are like a very simple call program. They don't do any meddling
  with the data at all, so the end of line handling you'll have to worry
  about yourself.

  Let's start with an example of how you might use them. Imagine you
  have a small network at home and that you have one linux machine
  acting as your Linux radio gateway and another machine, lets say a BPQ
  node connected to it via an ethernet connection.

  Normally if you wanted radio users to be able to connect to the BPQ
  node they would either have to digipeat through your linux node, or
  connect to the node program on your linux node and then connect from
  it.  The ax25_call program can simplify this if it is called from the
  ax25d program.

  Imagine the BPQ node has the callsign VK2KTJ-9 and that the linux
  machine has the AX.25/ethernet port named `bpq'. Let us also imagine
  the Linux gateway machine has a radio port called `radio'.

  An entry in the /etc/ax25/ax25d.conf that looked like:

       [VK2KTJ-1 via radio]
       default    * * * *   *   *  *
                       root /usr/sbin/ax25_call ax25_call bpq %u vk2ktj-9

  would enable users to connect direct to `VK2KTJ-1' which would actu¡
  ally be the Linux ax25d daemon and then be automatically switched to
  an AX.25 connection to `VK2KTJ-9' via the `bpq' interface.

  There are all sorts of other possible configurations that you might
  try.  The `netrom_call' and `rose_call' utilities work in similar
  ways. One amateur has used this utility to make connections to a
  remote BBS easier. Normally the users would have to manually enter a
  long connection string to make the call so he created an entry that
  made the BBS appear as though it were on the local network by having
  his ax25d proxy the connection to the remote machine.

  18.  Configuring the Rose Uplink and Downlink commands

  If you are familiar with the ROM based Rose implementation you will be
  familiar with the method by which AX.25 users make calls across a Rose
  network. If a users local Rose node has the callsign VK2KTJ-5 and the
  AX.25 user wants to connect to VK5XXX at remote Rose node 5050882960
  then they would issue the command:

       c vk5xxx v vk2ktj-5 5050 882960

  At the remote node, VK5XXX would see an incoming connection with the
  local AX.25 users callsign and being digipeated via the remote Rose
  nodes callsign.

  The Linux Rose implementation does not support this capability in the
  kernel, but there are two application programs called rsuplnk and
  rsdwnlnk which perform this function.

  18.1.  Configuring a Rose downlink

  To configure your Linux machine to accept a Rose connection and
  establish an AX.25 connection to any destination callsign that is not
  being listened for on your machine you need to add an entry to your
  /etc/ax25/ax25d.conf file. Normally you would configure this entry to
  be the default behaviour for incoming Rose connections. For example
  you might have Rose listeners operating for destinations like NODE-0
  or HEARD-0 that you wish to handle locally, but for all other
  destination calls you may want to pass them to the rsdwnlink command
  and assume they are AX.25 users.

  A typical configuration would look like:

       #
       {* via rose}
       NOCALL   * * * * * *  L
       default  * * * * * *  - root  /usr/sbin/rsdwnlnk rsdwnlnk 4800 vk2ktj-5
       #

  With this configuration any user who established a Rose connection to
  your Linux nodes address with a destination call of something that you
  were not specifically listening for would be converted into an AX.25
  connection on the AX.25 port named 4800 with a digipeater path of
  VK2KTJ-5.

  18.2.  Configuring a Rose uplink

  To configure your Linux machine to accept AX.25 connections in the
  same way that a ROM Rose node would you must add an entry into your
  /etc/ax25/ax25d.conf file that looks similar to the following:

       #
       [VK2KTJ-5* via 4800]
       NOCALL   * * * * * *  L
       default  * * * * * *  - root  /usr/sbin/rsuplnk rsuplnk rose
       #

  Note the special syntax for the local callsign. The `*' character
  indicates that the application should be invoked if the callsign is
  heard in the digipeater path of a connection.

  This configuration would allow an AX.25 user to establish Rose calls
  using the example connect sequence presented in the introduction.
  Anybody attempting to digipeat via VK2KTJ-5 on the AX.25 port named
  4800 would be handled by the rsuplnk command.

  19.  Associating AX.25 callsigns with Linux users.

  There are a number of situations where it is highly desirable to
  associate a callsign with a linux user account. One example might be
  where a number of amateur radio operators share the same linux machine
  and wish to use their own callsign when making calls. Another is the
  case of PMS users wanting to talk to a particular user on your
  machine.

  The AX.25 software provides a means of managing this association of
  linux user account names with callsigns. We've mentioned it once
  already in the PMS section, but I'm spelling it out here to be sure
  you don't miss it.

  You make the association with the axparms command. An example looks
  like:

       # axparms -assoc vk2ktj terry

  This command associates that AX.25 callsign vk2ktj with the user terry
  on the machine. So, for example, any mail for vk2ktj on the pms will
  be sent to Linux account terry.

  Remember to put these associations into your rc file so that they are
  available each time your reboot.

  Note you should never associate a callsign with the root account as
  this can cause configuration problems in other programs.

  20.  HOWTO link NOS and the Linux kernel networking software

  Many people like to run some version of NOS under Linux because it has
  all of the features and facilities they are used to. Most of those
  people would also like to have the NOS running on their machine
  capable of talking to the Linux kernel so that they can offer some of
  the linux capabilities to radio users.

  20.1.  Linking NOS and Linux using a pipe device

  Brandon S. Allbery, KF8NH, contributed the following information to
  explain how to interconnect the NOS running on a Linux machine with
  the kernel code using the Linux pipe device.

  Since both Linux and NOS support the slip protocol it is possible to
  link the two together by creating a slip link. You could do this by
  using two serial ports with a loopback cable between them, but this
  would be slow and costly. Linux provides a feature that many other
  Unix-like operating systems provide called `pipes'. These are special
  pseudo devices that look like a standard tty device to software but in
  fact loopback to another pipe device. To use these pipes the first
  program must open the master end of the pipe, and the open then the
  second program can open the slave end of the pipe. When both ends are
  open the programs can communicate with each other simply by writing
  characters to the pipes in the way they would if they were terminal
  devices.

  To use this feature to connect the Linux Kernel and a copy of NOS, or
  some other program you first must choose a pipe device to use. You can
  find one by looking in your /dev directory. The master end of the
  pipes are named: ptyp[1-f] and the slave end of the pipes are known
  as: ttyp[1-f]. Remember they come in pairs, so if you select
  /dev/ptypf as your master end then you must use /dev/ttypf as the
  slave end.

  Once you have chosen a pipe device pair to use you should allocate the
  master end to you linux kernel and the slave end to the NOS program,
  as the Linux kernel starts first and the master end of the pipe must
  be opened first.  You must also remember that your Linux kernel must
  have a different IP address to your NOS, so you will need to allocate
  a unique address for it if you haven't already.

  You configure the pipe just as if it were a serial device, so to
  create the slip link from your linux kernel you can use commands
  similar to the following:

       # /sbin/slattach -s 38400 -p slip /dev/ptypf &
       # /sbin/ifconfig sl0 broadcast 44.255.255.255 pointopoint 44.70.248.67 /
               mtu 1536 44.70.4.88
       # /sbin/route add 44.70.248.67 sl0
       # /sbin/route add -net 44.0.0.0 netmask 255.0.0.0 gw 44.70.248.67

  In this example the Linux kernel has been given IP address 44.70.4.88
  and the NOS program is using IP address 44.70.248.67. The route
  command in the last line simply tells your linux kernel to route all
  datagrams for the amprnet via the slip link created by the slattach
  command. Normally you would put these commands into your
  /etc/rc.d/rc.inet2 file after all your other network configuration is
  complete so that the slip link is created automatically when you
  reboot.  Note: there is no advantage in using cslip instead of slip as
  it actually reduces performance because the link is only a virtual one
  and occurs fast enough that having to compress the headers first takes
  longer than transmitting the uncompressed datagram.

  To configure the NOS end of the link you could try the following:

  # you can call the interface anything you want; I use "linux" for convenience.
  attach asy ttypf - slip linux 1024 1024 38400
  route addprivate 44.70.4.88 linux

  These commands will create a slip port named `linux' via the slave end
  of the pipe device pair to your linux kernel, and a route to it to
  make it work. When you have started NOS you should be able to ping and
  telnet to your NOS from your Linux machine and vice versa. If not,
  double check that you have made no mistakes especially that you have
  the addresses configured properly and have the pipe devices around the
  right way.

  21.  The /proc/ file system entries.

  The /proc filesystem contains a number of files specifically related
  to the AX25 and NetRom kernel software. These files are normally used
  by the AX52 utilities, but they are plainly formatted so you may be
  interested in reading them. The format is fairly easily understood so
  I don't think much explanation will be necessary.

     /proc/net/arp
        contains the list of Address Resolution Protocol mappings of IP
        addresses to MAC layer protocol addresses. These can can AX.25,
        ethernet or some other MAC layer protocol.

     /proc/net/ax25
        contains a list of AX.25 sockets opened. These might be
        listening for a connection, or active sessions.

     /proc/net/ax25_bpqether
        contains the AX25 over ethernet BPQ style callsign mappings.

     /proc/net/ax25_calls
        contains the linux userid to callsign mappings set my the
        axparms -assoc command.

     /proc/net/ax25_route
        contains AX.25 digipeater path information.

     /proc/net/nr
        contains a list of NetRom sockets opened. These might be
        listening for a connection, or active sessions.

     /proc/net/nr_neigh
        contains information about the NetRom neighbours known to the
        NetRom software.

     /proc/net/nr_nodes
        contains information about the NetRom nodes known to the NetRom
        software.

     /proc/net/rose
        contains a list of Rose sockets opened. These might be listening
        for a connection, or active sessions.

     /proc/net/rose_nodes
        contains a mapping of Rose destinations to Rose neighbours.

     /proc/net/rose_neigh
        contains a list of known Rose neighbours.

     /proc/net/rose_routes
        contains a list of all established Rose connections.

  22.  Some sample configurations.

  Following are examples of the most common types of configurations.
  These are guides only as there are as many ways of configuring your
  network as there are networks to configure, but they may give you a
  start.

  22.1.  Small Ethernet LAN with Linux as a router to Radio LAN

  Many of you may have small local area networks at home and want to
  connect the machines on that network to your local radio LAN. This is
  the type of configuration I use at home. I arranged to have a suitable
  block of addresses allocated to me that I could capture in a single
  route for convenience and I use these on my Ethernet LAN. Your local
  IP coordinator will assist you in doing this if you want to try it as
  well. The addresses for the Ethernet LAN form a subset of the radio
  LAN addresses. The following configuration is the actual one for my
  linux router on my network at home:

                                                 .      .   .    .    . .
         ---                                .
          | Network       /---------\     .    Network
          | 44.136.8.96/29|         |    .     44.136.8/24        \ | /
          |               | Linux   |   .                          \|/
          |               |         |  .                            |
          |          eth0 | Router  |  .  /-----\    /----------\   |
          |---------------|         |-----| TNC |----| Radio    |---/
          |   44.136.8.97 |  and    |  .  \-----/    \----------/
          |               |         | sl0
          |               | Server  | 44.136.8.5
          |               |         |    .
          |               |         |     .
          |               \_________/       .
         ---                                     .      .   .    .    . .

  #!/bin/sh
  # /etc/rc.net
  # This configuration provides one KISS based AX.25 port and one
  # Ethernet device.

  echo "/etc/rc.net"
  echo "  Configuring:"

  echo -n "    loopback:"
  /sbin/ifconfig lo 127.0.0.1
  /sbin/route add 127.0.0.1
  echo " done."

  echo -n "    ethernet:"
  /sbin/ifconfig eth0 44.136.8.97 netmask 255.255.255.248 \
                  broadcast 44.136.8.103 up
  /sbin/route add 44.136.8.97 eth0
  /sbin/route add -net 44.136.8.96 netmask 255.255.255.248 eth0
  echo " done."

  echo -n "    AX.25: "
  kissattach -i 44.136.8.5 -m 512 /dev/ttyS1 4800
  ifconfig sl0 netmask 255.255.255.0 broadcast 44.136.8.255
  route add -host 44.136.8.5 sl0
  route add -net 44.136.8.0 window 1024 sl0

  echo -n "    Netrom: "
  nrattach -i 44.136.8.5 netrom

  echo "  Routing:"
  /sbin/route add default gw 44.136.8.68 window 1024 sl0
  echo "    default route."
  echo done.

  # end

  /etc/ax25/axports

       # name  callsign        speed   paclen  window  description
       4800    VK2KTJ-0        4800    256     2       144.800 MHz

  /etc/ax25/nrports

       # name  callsign        alias   paclen  description
       netrom  VK2KTJ-9        LINUX   235     Linux Switch Port

  /etc/ax25/nrbroadcast

       # ax25_name     min_obs def_qual        worst_qual      verbose
       4800            1       120             10              1

  ╖  You must have IP_FORWARDING enabled in your kernel.

  ╖  The AX.25 configuration files are pretty much those used as
     examples in the earlier sections, refer to those where necessary.

  ╖  I've chosen to use an IP address for my radio port that is not
     within my home network block. I needn't have done so, I could have
     easily used 44.136.8.97 for that port too.

  ╖  44.136.8.68 is my local IPIP encapsulated gateway and hence is
     where I point my default route.

  ╖  Each of the machines on my Ethernet network have a route:

       route add -net 44.0.0.0 netmask 255.0.0.0 \
               gw 44.136.8.97 window 512 mss 512 eth0

  The use of the mss and window parameters means that I can get optimum
  performance from both local Ethernet and radio based connections.

  ╖  I also run my smail, http, ftp and other daemons on the router
     machine so that it needs to be the only machine to provide others
     with facilities.

  ╖  The router machine is a lowly 386DX20 with a 20Mb harddrive and a
     very minimal linux configuration.

  22.2.  IPIP encapsulated gateway configuration.

  Linux is now very commonly used for TCP/IP encapsulated gateways
  around the world. The new tunnel driver supports multiple encapsulated
  routes and makes the older ipip daemon obsolete.

  A typical configuration would look similar to the following.

                                                 .      .   .    .    . .
         ---                                .
          | Network       /---------\     .    Network
          | 154.27.3/24   |         |    .     44.136.16/24       \ | /
          |               | Linux   |   .                          \|/
          |               |         |  .                            |
          |          eth0 | IPIP    |  .  /-----\    /----------\   |
       ---|---------------|         |-----| TNC |----| Radio    |---/
          |   154.27.3.20 | Gateway |  .  \-----/    \----------/
          |               |         | sl0
          |               |         | 44.136.16.1
          |               |         |    .
          |               |         |     .
          |               \_________/       .
         ---                                     .      .   .    .    . .

  The configuration files of interest are:

  # /etc/rc.net
  # This file is a simple configuration that provides one KISS AX.25
  # radio port, one Ethernet device, and utilises the kernel tunnel driver
  # to perform the IPIP encapsulation/decapsulation
  #
  echo "/etc/rc.net"
  echo "  Configuring:"
  #
  echo -n "    loopback:"
  /sbin/ifconfig lo 127.0.0.1
  /sbin/route add 127.0.0.1
  echo " done."
  #
  echo -n "    ethernet:"
  /sbin/ifconfig eth0 154.27.3.20 netmask 255.255.255.0 \
                  broadcast 154.27.3.255 up
  /sbin/route add 154.27.3.20 eth0
  /sbin/route add -net 154.27.3.0 netmask 255.255.255.0 eth0
  echo " done."
  #
  echo -n "    AX.25: "
  kissattach -i 44.136.16.1 -m 512 /dev/ttyS1 4800
  /sbin/ifconfig sl0 netmask 255.255.255.0 broadcast 44.136.16.255
  /sbin/route add -host 44.136.16.1 sl0
  /sbin/route add -net 44.136.16.0 netmask 255.255.255.0 window 1024 sl0
  #
  echo -n "    tunnel:"
  /sbin/ifconfig tunl0 44.136.16.1 mtu 512 up
  #
  echo done.
  #
  echo -n "Routing ... "
  source /etc/ipip.routes
  echo done.
  #
  # end.

  and:

       # /etc/ipip.routes
       # This file is generated using the munge script
       #
       /sbin/route add -net 44.134.8.0 netmask 255.255.255.0 tunl0 gw 134.43.26.1
       /sbin/route add -net 44.34.9.0 netmask 255.255.255.0 tunl0 gw 174.84.6.17
       /sbin/route add -net 44.13.28.0 netmask 255.255.255.0 tunl0 gw 212.37.126.3
          ...
          ...
          ...

  /etc/ax25/axports

       # name  callsign        speed   paclen  window  description
       4800    VK2KTJ-0        4800    256     2       144.800 MHz

  Some points to note here are:

  ╖  The new tunnel driver uses the gw field in the routing table in
     place of the pointopoint parameter to specify the address of the
     remote IPIP gateway. This is why it now supports multiple routes
     per interface.

  ╖  You can configure two network devices with the same address.  In
     this example both the sl0 and the tunl0 devices have been
     configured with the IP address of the radio port. This is done so
     that the remote gateway sees the correct address from your gateway
     in encapsulated datagrams sent to it.

  ╖  The route commands used to specify the encapsulated routes can be
     automatically generated by a modified version of the munge script.
     This is included below. The route commands would then be written to
     a separate file and read in using the bash source /etc/ipip.routes
     command (assuming you called the file with the routing commands
     /etc/ipip.routes) as illustrated. The source file must be in the
     NOS route command format.

  ╖  Note the use of the window argument on the route command. Setting
     this parameter to an appropriate value improves the performance of
     your radio link.

  The new tunnel-munge script:

  #!/bin/sh
  #
  # From: Ron Atkinson <[e-mail]>
  #
  #  This script is basically the 'munge' script written by Bdale N3EUA
  #  for the IPIP daemon and is modified by Ron Atkinson N8FOW. It's
  #  purpose is to convert a KA9Q NOS format gateways route file
  #  (usually called 'encap.txt') into a Linux routing table format
  #  for the IP tunnel driver.
  #
  #        Usage: Gateway file on stdin, Linux route format file on stdout.
  #               eg.  tunnel-munge < encap.txt > ampr-routes
  #
  # NOTE: Before you use this script be sure to check or change the
  #       following items:
  #
  #     1) Change the 'Local routes' and 'Misc user routes' sections
  #        to routes that apply to your own area (remove mine please!)
  #     2) On the fgrep line be sure to change the IP address to YOUR
  #        gateway Internet address. Failure to do so will cause serious
  #        routing loops.
  #     3) The default interface name is 'tunl0'. Make sure this is
  #        correct for your system.

  echo "#"
  echo "# IP tunnel route table built by $LOGNAME on `date`"
  echo "# by tunnel-munge script v960307."
  echo "#"
  echo "# Local routes"
  echo "route add -net 44.xxx.xxx.xxx netmask 255.mmm.mmm.mmm dev sl0"
  echo "#"
  echo "# Misc user routes"
  echo "#"
  echo "# remote routes"

  fgrep encap | grep "^route" | grep -v " XXX.XXX.XXX.XXX" | \
  awk '{
          split($3, s, "/")
          split(s[1], n,".")
          if      (n[1] == "")    n[1]="0"
          if      (n[2] == "")    n[2]="0"
          if      (n[3] == "")    n[3]="0"
          if      (n[4] == "")    n[4]="0"
          if      (s[2] == "1")   mask="128.0.0.0"
          else if (s[2] == "2")   mask="192.0.0.0"
          else if (s[2] == "3")   mask="224.0.0.0"
          else if (s[2] == "4")   mask="240.0.0.0"
          else if (s[2] == "5")   mask="248.0.0.0"
          else if (s[2] == "6")   mask="252.0.0.0"
          else if (s[2] == "7")   mask="254.0.0.0"
          else if (s[2] == "8")   mask="255.0.0.0"
          else if (s[2] == "9")   mask="255.128.0.0"
          else if (s[2] == "10")  mask="255.192.0.0"
          else if (s[2] == "11")  mask="255.224.0.0"
          else if (s[2] == "12")  mask="255.240.0.0"
          else if (s[2] == "13")  mask="255.248.0.0"
          else if (s[2] == "14")  mask="255.252.0.0"
          else if (s[2] == "15")  mask="255.254.0.0"
          else if (s[2] == "16")  mask="255.255.0.0"
          else if (s[2] == "17")  mask="255.255.128.0"
          else if (s[2] == "18")  mask="255.255.192.0"
          else if (s[2] == "19")  mask="255.255.224.0"
          else if (s[2] == "20")  mask="255.255.240.0"
          else if (s[2] == "21")  mask="255.255.248.0"
          else if (s[2] == "22")  mask="255.255.252.0"
          else if (s[2] == "23")  mask="255.255.254.0"
          else if (s[2] == "24")  mask="255.255.255.0"
          else if (s[2] == "25")  mask="255.255.255.128"
          else if (s[2] == "26")  mask="255.255.255.192"
          else if (s[2] == "27")  mask="255.255.255.224"
          else if (s[2] == "28")  mask="255.255.255.240"
          else if (s[2] == "29")  mask="255.255.255.248"
          else if (s[2] == "30")  mask="255.255.255.252"
          else if (s[2] == "31")  mask="255.255.255.254"
          else                    mask="255.255.255.255"

  if (mask == "255.255.255.255")
          printf "route add -host %s.%s.%s.%s gw %s dev tunl0\n"\
                  ,n[1],n[2],n[3],n[4],$5
  else
          printf "route add -net %s.%s.%s.%s gw %s netmask %s dev tunl0\n"\
                  ,n[1],n[2],n[3],n[4],$5,mask
   }'

  echo "#"
  echo "# default the rest of amprnet via mirrorshades.ucsd.edu"
  echo "route add -net 44.0.0.0 gw 128.54.16.18 netmask 255.0.0.0 dev tunl0"
  echo "#"
  echo "# the end"

  23.  AX.25, NetRom, Rose network programming.

  Probably the biggest advantage of using the kernel based
  implementations of the amateur packet radio protocols is the ease with
  which you can develop applications and programs to use them.

  While the subject of Unix Network Programming is outside the scope of
  this document I will describe the elementary details of how you can
  make use of the AX.25, NetRom and Rose protocols within your software.

  23.1.  The address families.

  Network programming for AX.25, NetRom and Rose is quite similar to
  programming for TCP/IP under Linux. The major differences being the
  address families used, and the address structures that need to be
  mangled into place.

  The address family names for AX.25, NetRom and Rose are AF_AX25,
  AF_NETROM and AF_ROSE respectively.

  23.2.  The header files.

  You must always include the `ax25.h' header file, and also the
  `netrom.h' or `rose.h' header files if you are dealing with those
  protocols. Simple top level skeletons would look something like the
  following:

  For AX.25:

       #include <ax25.h>
       int s, addrlen = sizeof(struct full_sockaddr_ax25);
       struct full_sockaddr_ax25 sockaddr;
       sockaddr.fsa_ax25.sax25_family = AF_AX25

  For NetRom:

       #include <ax25.h>
       #include <netrom.h>
       int s, addrlen = sizeof(struct full_sockaddr_ax25);
       struct full_sockaddr_ax25 sockaddr;
       sockaddr.fsa_ax25.sax25_family = AF_NETROM;

  For Rose:

       #include <ax25.h>
       #include <rose.h>
       int s, addrlen = sizeof(struct sockaddr_rose);
       struct sockaddr_rose sockaddr;
       sockaddr.srose_family = AF_ROSE;

  23.3.  Callsign mangling and examples.

  There are routines within the lib/ax25.a library built in the AX25
  utilities package that manage the callsign conversions for you. You
  can write your own of course if you wish.

  The user_call utilities are excellent examples from which to work. The
  source code for them is included in the AX25 utilities package.  If
  you spend a little time working with those you will soon see that 90
  percent of the work is involved in just getting ready to open the
  socket.  Actually making the connection is easy, the preparation takes
  time.

  The example are simple enough to not be very confusing. If you have
  any questions, you should feel to direct them to the linux-hams
  mailing list and someone there will be sure to help you.

  24.  Discussion relating to Amateur Radio and Linux.

  There are various places that discussion relating to Amateur Radio and
  Linux take place. They take place in the comp.os.linux.* newsgroups,
  they also take place on the HAMS list on vger.rutgers.edu. Other
  places where they are held include the tcp-group mailing list at
  ucsd.edu (the home of amateur radio TCP/IP discussions), and you might
  also try the #linpeople channel on the linuxnet irc network.

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

       [e-mail]

  with the line:

       subscribe linux-hams

  in the message body. The subject line is ignored.

  The linux-hams mailing list is archived at:

  zone.pspt.fi <http://zone.pspt.fi/archive/linux-hams/> and
  zone.oh7rba.ampr.org <http://zone.oh7rba.ampr.org/archive/linux-
  hams/>.  Please use the archives when you are first starting, because
  many common questions are answered there.

  To join the tcp-group send mail to:

       [e-mail]

  with the line:

       subscribe tcp-group

  in the body of the text.

  Note: Please remember that the tcp-group is primarily for discussion
  of the use of advanced protocols, of which TCP/IP is one, in Amateur
  Radio. Linux specific questions should not ordinarily go there.

  25.  Acknowledgements.

  The following people have contributed to this document in one way or
  another, knowingly or unknowingly. In no particular order (as I find
  them): Jonathon Naylor, Thomas Sailer, Joerg Reuter, Ron Atkinson,
  Alan Cox, Craig Small, John Tanner, Brandon Allbery, Hans Alblas,
  Klaus Kudielka, Carl Makin.

  26.  Copyright.

  The AX25-HOWTO, information on how to install and configure some of
  the more important packages providing AX25 support for Linux.
  Copyright (c) 1996 Terry Dawson.

  This program is free software; you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation; either version 2 of the License, or (at
  your option) any later version.

  This program is distributed in the hope that it will be useful, but
  WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
  General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program; if not, write to the:

  Free Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139,
  USA.