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Linux PPP HOWTO
Al Longyear, longyear@netcom.com
v1.11, 12 July 1995
This document contains a list the most Frequently Asked Questions
(FAQ) about PPP for Linux (and their answers). It is really not a
HOWTO, but is in `classical' Question / Answer form.
1. Preface
Please send any corrections to longyear@netcom.com.
This is but one of the Linux HOWTO/FAQ documents. You can get the
HOWTO's from sunsite.unc.edu:/pub/Linux/docs/HOWTO (this is the
`official' place) or via WWW from the Linux Documentation home page
<http://sunsite.unc.edu/mdw/linux.hmtl>. You cannot rely on the
HOWTO's being posted to comp.os.linux.answers, as some news feeds have
complained about their size.
Throughout this document, I have used the word `remote' to mean `the
system at the other end of the modem link'. It is also called `peer'
in the PPP documentation. Another name for this is called the
`gateway' when the term is use for routing. Its IP address will show
as the `P-t-P' address if you use ifconfig.
Microsoft is a registered trademark of Microsoft Corporation. Morning
Star is a registered trademark of Morning Star Technologies
Incorporated. All other products mentioned are trademarks of their
respective companies.
2. General information
2.1. What is PPP?
PPP, or Point-to-Point Protocol, is a recognized `official' internet
protocol. It is a protocol used to exchange IP frames (and others)
over a serial link. The current RFC for PPP is 1661. There are many
related ones.
Contrary to what some people think, it does not mean "Peer to Peer
Processing"; although you may do peer-peer communications using TCP/IP
over a PPP link.
2.2. My university (company) does not support PPP. Can I use PPP?
In general, no. A `classical' PPP implementation requires that you
make changes to the routes and network devices supported by the
operating system. This may mean that you will have to rebuild the
kernel for the remote computer.
This is not a job for a general user. If you can convince your
administration people that PPP is a `good thing' then you stand a
chance of getting it implemented. If you can't, then you probably
can't use PPP.
However, if you are using a system which is supported by the people
who are marketing the "TIA" (The Internet Adapter) package, then there
is hope. I do not have much information on this package, however, from
what I have found, they plan to support PPP in "the next version". (My
information may be old. Contact them directly. Information on TIA is
available at ftp.marketplace.com in the /pub/tia directory.)
If your system is not supported by TIA and you can't convince the
admin group to support PPP then you should use the `term' package.
Some service providers will object to you running `term'. They have
many different reasons, however the most common is `security
concerns'.
There is a version of TIA for Linux.
2.3. Where is PPP?
It is in two parts. The first part is in the kernel. In the kernels
from 1.1.13, the driver is part of the network system drivers.
Do not replace the driver in the kernel with a version from the pppd
package!!!
The second part is the `daemon' process, pppd. This is a required
process. The source to it is in the file ppp-2.1.2c.tar.gz located on
sunsite.unc.edu in the /pub/Linux/system/Network/serial directory.
For kernels before 1.1.13, the necessary driver is included in the
daemon code.
2.4. I just obtained PPP. What do I do with it?
Read The Fine Material available.
Start by reading the README file and then the README.linux file. The
documentation sources are listed below.
2.5. (Where's the documentation? Is there a HOWTO?, etc.) Where are
additional sources of information for PPP?
There are several sources of information for the PPP protocol as
implemented under Linux.
o The README file in the source package.
o The README.linux file in the source package.
o The Net-2-HOWTO document.
o The Network Administration Guide.
o The pppd man page.
o The PPP FAQ document. (This is not it, by the way.)
The HOWTO file is stored in the usual place for the Linux HOWTOs.
That is currently on sunsite.unc.edu in the directory
/pub/Linux/docs/HOWTO.
The Network Administration Guide is available in the
/pub/Linux/docs/LPD/network-guide directory on sunsite. It is also
published by O'Riellly and Associates. So, if you want a really
professional document, then buy a copy from your local bookstore.
The `man' pages are included in the source package. You will probably
have to move them to the normal man directory, /usr/man/man8 before
the man command may find them. Alternately, you may use nroff and
more to view them directly.
The PPP faq document describes the PPP protocol itself and the various
implementations. You will find the FAQ for the usenet news group,
comp.protocols.PPP, archived on rtfm.mit.edu in the /usenet directory.
It is in eight parts at the present time.
2.6. Where should I post questions about PPP?
The primary usenet group for the PPP implementations is
comp.protocols.PPP. Use this group for general questions such as "How
do I use pppd?" or "Why doesn't this work?".
Questions such as "Why wont pppd compile?" are generally linux related
and belong on the comp.os.linux.networking group.
Please don't use comp.os.linux.help.
2.7. The PPP software doesn't work. HELP!!!
This is one of the most sickening questions. I realize that this is a
plea for help. However, it is practically useless to post this message
with no other information. I, and most others, will only ignore it.
Please see the question regarding errors which normally occur at the
modem's disconnection. They are not the cause of a problem, only a
symptom. Posting a message with only those errors is also meaningless.
What is needed is the output of the system log (syslog) when you run
the pppd program with the option `debug'. In addition, if you are
using chat then please use the `-v' option to run the sequence with
verbose output.
Please include the output from the kernel's startup. This shows the
various kernel hardware information such as your UART type, PPP
version, etc.
Please include all information that you can relating to the problem.
However your system configuration, disk drive configuration, terminal
type, mouse location and button status, etc. are irrelevant. What is
important is the system to which your are trying to contact, the PPP
(or terminal server) that they are using, the modem types and speed
that you are using, etc.
Take care and go through the output. Remove the references to the
telephone number, your account name, and the password. They are not
important to analyzing the problem and would pose a security risk to
you if you published them to usenet. Also discard the lines which
neither come from the kernel nor pppd.
Do NOT run the pppd program with the option `kdebug 7' and post that!
If the problem warrants examining the data stream, then you will be
contacted by email and asked to mail the trace. Usenet already costs
too much for too many people.
Information is written to various levels. The debug information is
written to the debug level. The informational messages are written to
the info level. The errors are written to the error level. Please
include all levels the the `local2' group which come from the pppd
process.
In addition, please do not delete the time stamp information. It is
important.
2.8. How do I use PPP with a system which uses dynamic IP assign-
ments? It assigns a different IP address to me with each call.
The assignment of the local IP address is a function of the options
given to pppd and the IPCP protocol. You should use the `magic' IP
address of 0.0.0.0 if you must specify the local IP address. Most
people simply leave the local IP address out of the option list.
The other option which is closely tied to this is called
`noipdefault'. The noipdefault option instructs the pppd process to
not attempt to guess the local IP address from your hostname and the
IP addresses in the /etc/hosts file. Most people use this option when
the IP address is dynamically assigned. However, this option does not
mean `use dynamic IP addresses'. The use of dynamic IP addresses is
automatic when the local IP address is not given.
2.9. How do I know what IP address was given to me when it is dynami-
cally assigned?
Use the /etc/PPP/ip-up hook. The local IP address is the fourth
parameter. This will be executed when pppd knows the IP address for
the local system. The fifth parameter is the remote IP address if you
should wish to know this value as well.
2.10. Can I use the same local IP address for each line of a PPP
server?
Yes. The local address is not significant to the local system. You
must have a unique remote IP address. The routing is performed based
upon the remote IP address and not the local IP address.
3. Other implementations
3.1. Do you know of a implementation for PPP other than Linux? I
would like one for HP-UX, or AIX, or ... (you fill in the blank) ?
Check the PPP FAQ document mentioned above.
AIX is due to be supported in the 2.2 version of the pppd process.
HP-UX is, to my knowledge, only supported by the Morning Star
commercial package.
If you don't find one listed then post to the comp.protocols.PPP group
and not the Linux group.
(Please don't mail me asking for "Do you know of a PPP package for
..."? These requests will now be `appropriately' filed. ;-))
3.2. Did you know that there is a program called `dp'?
Yes, we know. The dp package was considered very early in the
development stage quite a few months back. It is nice. It supports
'demand dial'. It also only works with systems which support streams.
This is primarily the SunOS (Solaris) operating systems.
Linux, at the present time, does not supports streams.
There are several other packages for PPP available on the `net'. The
`portable PPP' package is very much like the TIA code. There is
another package called simply `PPP'. There is code for PPP in the KA9Q
package.
Of all of the packages available, the pppd package was the closest to
the requirements and functions of Linux to warrant the port.
(If you want more information about these other packages, ask in the
comp.protocols.PPP group!)
3.3. What RFCs describe the PPP protocol?
The current implementation of PPP is a mixture of several. The major
portion of the PPP code is written against the RFCs 1331 and 1332.
These RFCs were later obsoleted. 1331 was replaced by 1548 and that,
in turn, was obsoleted by 1661 six months later.
Most implementations of PPP will be happy to talk to the Linux PPP
code.
A complete list is in the PPP faq.
[to quote the FAQ document]:
All of 1134, 1171, and 1172 (and 1055, for that matter :-)
have been obsoleted. They're interesting only if you want to
debug a connection with an ancient PPP implementation, and
you're wondering why (e.g.) it asked you for IPCP option 2
with a length of only 4, and Compression-Type 0x0037.
(There's a lot of that still running around - be careful out
there.)
Linux PPP will not support this.
4. Compatibility
4.1. Can PPP talk to a SLIP interface?
No. SLIP works with SLIP. PPP works with PPP.
Some vendors may offer products which work both as SLIP and PPP.
However, they must be configured to run in one mode or the other.
There is no present method to determine, based upon the protocol
passed at the time of a connection, which combination of SLIP
protocols or PPP is being requested.
4.2. Which is better? PPP or SLIP?
IT DEPENDS UPON MANY FACTORS. The people who post this type of
question have usually not read the Net-2-HOWTO document.
A good technical discussion is available at Morning Star's www server,
www.morningstar.com.
4.3. Is CHAP or PAP better for authentication?
If you have the choice, use CHAP. Failing that, PAP is better than
nothing.
5. Authentication files
5.1. What goes into the /etc/PPP/pap-secrets file? Do you have a sam-
ple?
The PAP protocol is most often implemented as your user name and
password. You need to include the name of the remote system, your
account name, and the password. If the user on abbot wishes to call
costello, the entry would be similar to the following.
#remote account password IP address list
* abbot firstbase
5.2. What goes into the /etc/PPP/chap-secrets file? Do you have a
sample?
The most common problem is that people don't recognize that CHAP deals
with a pair of secrets. Both computers involved in the link must have
both secrets to work.
For example, if abbot wants to talk to costello, then abbot's file
would have:
#local remote secret IP address list
abbot costello firstbase
costello abbot who
And costello's file would have:
#local remote secret IP address list
abbot costello firstbase
costello abbot who
6. Construction problems
6.1. I get compile errors when I try to compile the kernel
With the release of the 1.2 kernel for Linux, the PPP driver is a
standard part of the network devices. Each kernel should include the
software necessary to make the PPP support within the kernel. Please
do not edit the PPP driver. It has been pre-configured for the kernel.
If you are attempting to run PPP on kernels prior to the 1.2, then
please consider upgrading the kernel. The 1.0 kernels require patching
to support the PPP driver. The 1.2 kernels supported PPP to some
degree, but also required changes depending upon the specific patch
level.
7. Problems running pppd
7.1. pppd wont run unless you are root
The pppd process needs to make changes to the networking system and
this can only be done if you are the root user. If you wish to run
pppd from other than the root user then the pppd program needs to be
secured 'suid to root'.
chown root pppd
chmod 4755 pppd
If you wish to control the pppd access to a select group of people,
then make the pppd process owned by the group and do not permit all
others to run the program.
7.2. The ppp-2.1.2d package says it needs the 4.6 libraries
Sorry, I goofed. You will have to forego the binaries and re-compile
the code yourself. It is easy. Go to the pppd directory, delete the
bad binary, and issue the command `make'. Go to the chat directory and
do the same if you want a corrected chat program.
You must have the C language compiler and GNU make installed to
rebuild the PPP software.
It turns out that when I compiled the ppp-2.1.2d package, while I used
the proper definitions, I used the 4.6 libraries. One of these days,
Al may finally get his act together . . . .
Or, you can get binaries from the Slackware 2.0.2 (or later) package.
They are in the PPP.tgz file in the `n' series of disks.
Please use the source in the ppp-2.1.2d to compile the code. The
source has been corrected over the `a' package.
7.3. unable to create pid file: no such file or directory
You need to create the directory /var/run. On earlier Slackware
distributions, this was a symbolic link to the /etc directory.
This is a warning. The PPP software will work normally in spite of
this message. However, the PPP-off script depends upon this file. It
is a good idea to create the directory or make the link to the
appropriate location.
The posix header, paths.h, defines the location for the pid file under
the name "_VAR_RUN". If you wish to use a different directory for PPP
and others, change the value for this define and rebuild the software.
7.4. /etc/PPP/options: no such file or directory
You need to create the directory /etc/PPP and have a file called
'options' in that directory. It needs to be readable by the pppd
process (root).
The file may be empty. To make an empty file use the `touch' command.
See the pppd man page, pppd.8, for a description of this file.
7.5. Could not determine local IP address
This happens with many configurations of the Telebit Netblazer. The
problem is not the terminal server, but the site which has not
configured the terminal server with a set of IP addresses.
The Netblazer does not have your IP address. You do not have your IP
address. The link will not work unless both IP addresses are known.
o The Netblazer does not have your IP address and you do not have
your IP address.
o The Netblazer does know its IP address and you do not have its IP
address.
The link will not work unless both IP addresses are known.
You must tell the Netblazer the IP addresses to be used. Use the local
IP address and the remote IP address as a parameter to the pppd
process.
Use the pppd option format of:
local_ip:remote_ip
(That is the local IP address, a colon, and the remote IP address.)
7.6. Could not determine remote IP address
See the previous answer.
7.7. I keep getting the message to the effect that the magic number
is always NAKed. The system will not connect.
There is a one in over four billion chance that the two systems have
chosen the same magic number. If you get a continual failure about the
magic number, the chances that this is a fluke will geometrically
reduce.
The two most common reasons for this failure are:
o The remote PPP software is not running when you think it is. Is
the remote system configured to run PPP? Is the PPP process in the
expected location? Is the privileges suitable so that you may run
it?
This would indicate that the shell is doing the local echo of the
data. This is the more common reason.
o The modem has disconnected immediately upon making the connection
and logging you on to the remote. Most modems are configured to
echo the data sent to them and you are seeing the local echo from
the modem.
In either case, the Linux system is sending data to the remote which
is being fed immediately back into the serial receiver. This is not an
acceptable condition. You have what is called a "loop".
7.8. protocol reject for protocol fffb
This usually occurs when you are trying to connect to a Xyplex
terminal server. Version 5.1 of the Xyplex terminal server software,
according to Xyplex, has numerous problems with PPP. It is strongly
recommended that you update the Xyplex software to at least version
5.3.
If you must use version 5.1, then use the pppd option "vj-max-slots 3"
to limit the number of slots to three. The problem on the Xyplex
server is that it will accept the request for the default 16 slots,
but fail to operate beyond the third slot. It should have return a NAK
frame with the limit, but it does not.
Alternately, you can disable the Van Jacobson header compression with
the option "-vj".
7.9. The PPP software connects, sends quite a few frames, but still
does not seem to connect. Why is that?
Examine the system log when you use the "debug" option. (You will need
the system log data anyway if you are going to ask for help.) If the
trace shows that it is sending the LCP-request frame over and over
again and the id number is not incrementing then you are not
exchanging frames with the remote PPP software.
Three common reasons for this are:
o You don't have the PPP software running on the other end. You are
sending the PPP frames to some other program which is probably
saying "What is this #$%^ ?"
Please make sure that you have the PPP software started on the
other end before you enter the PPP protocol sequence. Try to use a
normal modem program and go through the logon sequence that you
would normally do. Do you see the PPP frames being sent to you?
The PPP frames are fairly distinctive. They will be about 16
characters in length and contain several { characters. They should
not have a carriage return character after them and are sent out in
a burst with a pause between the bursts.
o The line is not "eight bit clean". This means that you need to have
eight data bits, no parity, and one stop bit. The PPP link
absolutely requires eight data bits.
The pppd software will automatically put the line into eight data
bits, no parity, and one stop bit. The remote must match this
configuration or framing and parity errors may occur.
PPP will escape characters. It is not possible for it to escape
bits as kermit does. PPP will not work with a seven bit
communications link.
There is a compile option in the PPP.c driver (part of the kernel)
called CHECK_CHARACTERS which will include additional code in the
driver to provide additional checking on the input characters. It
will be able to tell you if the parity was enabled or if the remote
system always sent the characters as seven bits.
o The remote is configured to require authentication such as PAP or
CHAP. You have not configured the local system to use this feature.
Therefore, the remote is discarding all of your frames until it
sees a valid authentication frame from you. Since you are not
configured to generate the frames, the IPCP frames which you send
are being ignored.
In this case, either configure the remote to not expect
authentication or configure the local system to do authentication
and supply the proper secrets.
Examine the receipt of the LCP configure frame. If it shows an
'auth' type, then the remote is configured for authentication.
7.10. I can't connect to the merit network.
Some users of the merit network have indicated that it needs PAP. Did
you try PAP authentication?
8. DIP
8.1. DIP does not have support for PPP's mode
The current version of dip-uri supports PPP in that it will execute
the pppd process when you execute `mode PPP'. However, there are many
options which are needed for the proper operation of pppd. Since dip
does not pass these to the program, they must be stored in the
/etc/PPP/options file.
The dip program controls the establishment of the SLIP link. It
controls the SLIP link with the aid of slattach, ifconfig, and route.
These programs may be used to establish a SLIP link. They are not
useful for the establishment of a PPP link.
The dip program may be used to dial the telephone and start the PPP
software on the remote system. It is best used in this mode as the
parameter to the `connect' option. However, you have the option to use
dip to control the link. It is not important how pppd be executed to
run the PPP link. It is only important that it be executed as it is a
mandatory program for the PPP protocol.
9. Process termination
9.1. Is there a `dip -k' for PPP?
No. There is no `dip -k'.
In the chat directory, there is a `PPP-off' script. This will stop the
PPP link in the same manner as the 'dip -k'.
I have included it below. (Cut it out. Store it in its own file. Make
the file executable with chmod.)
______________________________________________________________________
#!/bin/sh
DEVICE=ppp0
#
# If the ppp0 pid file is present then the program is running. Stop it.
if [ -r /var/run/$DEVICE.pid ]; then
kill -INT `cat /var/run/$DEVICE.pid`
#
# If the kill did not work then there is no process running for this
# pid. It may also mean that the lock file will be left. You may wish
# to delete the lock file at the same time.
if [ ! "$?" = "0" ]; then
rm -f /var/run/$DEVICE.pid
echo "ERROR: Removed stale pid file"
exit 1
fi
#
# Success. Let pppd clean up its own junk.
echo "PPP link to $DEVICE terminated."
exit 0
fi
#
# The PPP process is not running for ppp0
echo "ERROR: PPP link is not active on $DEVICE"
exit 1
______________________________________________________________________
9.2. PPP does not hangup the modem when it terminates
There are several reasons for this.
o Did you use the pppd `modem' parameter? This parameter controls
whether or not the pppd process is to control and honor the signals
reflecting the modem status. This parameter is explained in the man
page for pppd.
o Do you have the modem presenting the DCD signal and honoring DTR?
The Hayes sequence for this is usually "&C1". If you reset the
modem during the connection sequence with "ATZ" then ensure that
your modem is configured correctly.
The DTR signal is generated by the computer and instructs the modem
to disconnect. Hayes sequence for this is usually "&D1" or "&D2"
with "&D2" being the preferred setting for PPP. Many manufacturers
will ignore the DTR condition in their `factory defaults' setting.
o Did you use a cheap cable which does not pass the DCD signal?
Macintosh `Classic' cables are notorious for this problem. The
Macintosh Classic does not use this signal.
o For dial-in connections, did you exec the pppd process properly?
The pppd process should be `exec'ed from the script rather than
simply executed. If you attempt to simply run the pppd process then
it will be the shell which will receive the SIGHUP hangup signal
and not the pppd process.
The `shell' script should have a format similar to the following:
___________________________________________________________________
#!/bin/sh
exec pppd -detach modem ...
___________________________________________________________________
10. Data Transfer related issues
10.1. The ftp transfers seems to die when I do a `put' operation.
They will work correctly if I `get' a file. Why?
Do you have the flow control enabled? Flow control is set by the pppd
option crtscts for RTS/CTS and xonxoff for XON/XOFF. If you don't
enable the flow control then you will probably overrun the modem's
buffers and this will prove to be disastrous with vj header
compression.
10.2. How do I use XON/XOFF for flow control?
The better flow control is CTS/RTS. However, if you can not do the
hardware flow control with the signals CTS and RTS, then use XON/XOFF.
The following three steps need to be performed.
o You need to specify the pppd option xonxoff. This tells the pppd
process to configure the serial device for XON/XOFF flow control
and to load the two characters into the tty driver.
o You need to specify the XON and XOFF characters in the pppd
parameter asyncmap. This tells the remote system that is should
quote the XON and XOFF characters when it wishes to send them to
you. It is normally specified as the pppd parameter `asyncmap
a0000'.
o Of course, don't forget to tell the modem to use XON/XOFF flow
control. My ZyXEL modem uses a sequence `&R1&H4' to do this.
10.3. The modem seems to always connect at a strange rate. When I use
minicom, the modem will always use 14400. However, PPP is using 9600
or 7200 or even 2400. How do I fix this?
Put the desired rate as an option to the pppd process. If you don't
put the rate, then pppd process will use whatever rate is set
currently at the time. Not all programs will restore all of the
parameters to the previous settings properly upon exit. This may lead
to strange rates configured for the serial device.
10.4. The ftp transfers seems to be very slow when I do a `get' oper-
ation. The `put' operation is much faster. Why?
Did you specify the option:
asyncmap 0
when you ran pppd? If you forgot the option, the peer must quote
(double) all of the control characters in the range from 00 to 1F
(hex). This will result in a statistical loss of about 12.5% in speed
for all of the data which you receive.
Did you configure the remote system? If so, did you forget flow
control on its modem?
10.5. The proxyarp function fails to find the hardware address.
Use the ppp-2.1.2d.tar.gz package. The pppd process was erroneously
compiled with the 1.1.8 kernel and it used Net-3 rather than Net-2
definitions.
Additionally, you should refer to the proxy-ARP mini-HOWTO about the
requirements for using proxy-ARP.
11. Routing and other problems
11.1. My route to the remote keeps disappearing! It last for about 3
minutes and then the route just goes away. Help!
This is not a question for PPP.
Hint: DON'T RUN routed!
11.2. I can reach the remote server, but I can not get anywhere else.
Did you forget the `defaultroute' parameter to pppd? This parameter
adds a default route into your routing system so that frames to all
other IP addresses will be sent to the PPP device.
The PPP software will not replace the default route if you have one
already set when you run pppd. This is done to prevent people from
destroying their default route to the ethernet routers by accident. A
warning message is written to the system log if the defaultroute
parameter is not performed for this reason.
11.3. I have a default route and I still can't get anywhere else! Now
what?
The problem then is not with the local Linux system. It most likely is
routing problem on the remote end.
The remote system is not configured for `IP forwarding'. It is an RFC
requirement that this option NOT be enabled by default. You must
enable the option. For Linux systems, you will need to build the
kernel and specify that you want IP forwarding/gatewaying.
The remote computers need a route back to you just as you need a route
to them. This may be accomplished by one of four methods. Each has
advantages and limitations. You need to do one and only one of these.
o Use a host route. At each host on the remote system, add a host
route to your Linux IP address with the gateway being the terminal
server that you use for your local access. This will work if you
have a small number of host systems and a simple network without
bridges, routers, gateways, etc.
o Use a network route. Subdivide the remote IP addresses so that your
local Linux IP address and the remote terminal server address and
the remote terminal server's ethernet address is on the same IP
domain. This will work if you have the IP addresses to spare. It
will work very well if you have a Class-B IP domain and can afford
to put the all of the remote addresses on the same IP domain. Then
add a network route on each of the gateways and routers so that any
address of the remote network is sent to the terminal server. Most
configurations have many hosts but few routers. (At sii.com, we
have over 300 active host systems with only 3 routers.)
o Use gated on all of the gateways and on the terminal server. This
will cause the terminal server to broadcast to the gateways that it
can accept the frames for your IP address. Since the hosts will
have a default route to one of the gateways, the gateways will
generate the ICMP re-direct frame and the specific host will
automatically add its host route.
o Use proxy ARP on the terminal server. This will only work if your
remote IP address is in the same IP domain as one of the domains
for the network cards.
There is no clear solution. You must choose one of these.
If your remote router requires to receive RIP frames in order to
update the route to your system then you should use the bcastd program
on sunsite.unc.edu. This will generate the RIP frames without actually
running gated.
11.4. I can not ping my local IP address
You are not able to do this because you wont normally have a route to
the address. This is the normal operating environment.
If you wish to ping your own system then use the loopback address of
127.0.0.1.
You may be able to ping the remote address. However, some terminal
servers may not allow this as the address may be 'phony' to them. It
depends upon their environment.
In general, don't try to ping either address. Choose a third address
which is well known to be available on the remote network such as one
of your name server IP address.
While the PPP software will not perform this task, you may add the
route table entry yourself once the link has been established. The
syntax for the route statement is:
route add -host 192.187.163.32 lo
where the local IP address is represented as 192.187.163.32 in this
example. This will tell the network software to route all frames
destined to your local IP address to the loopback adapter. Once you
add the appropriate route to the local IP address then you may use
this address as the target to IP frames.
You will be responsible for deleting the route when the link goes
down.
12. Interactions with other PPP implementations
12.1. I am using a Trumpet (for MSDOS) and the connection simply ter-
minates. Why is this happening?
Trumpet does not like any VJ header compression. Use the pppd option
"-vj" to turn it off.
12.2. I am using dp-3.1.2 (with SunOS) and the system will not allow
me to use anything but ping, or nslookup. Why is this happening?
There is a bug in the 3.1.2 version of dp. Please get the 3.1.2a or
later file from the dp ftp home site harbor.ecn.purdue.ecu. Until you
can put the patch into dp, disable the vj header compression.
12.3. I can not connect to/with my Windows NT code (originally called
'Daytona')
Microsoft has chosen to support a non-standard authentication protocol
with Windows NT. That is their right to do so provided that they have
registered the protocol number with the IANA. (They have.) If the
`accept only Microsoft encrypted authentication' check box is set in
the phone book entry, the connection will not complete. This setting
mandates that the Windows NT system only exchange PPP authentication
with another Microsoft PPP implementation.
Linux does not support this authentication protocol.
If you have the option of changing the settings on the Windows NT
system then go to the Windows NT Phone Book settings, advanced,
security settings and ensure that the `Accept any authentication
including clear text' box is checked and the `accept only Microsoft
encrypted authentication' is not checked. The other checkboxes may be
checked or not as you see fit.
Then use PAP on the Linux side. Put your Windows NT account name and
password into the /etc/PPP/pap-secrets file.
The Microsoft authentication sequence is a PAP style authentication
with their DES encryption algorithm for the passwords. Normal PAP
sends the passwords in clear text. This would violate their C2
security goals.
Versions of the Linux PPP code earlier than 2.1.2c have a flaw in
their decoding of the authentication request. They will not work with
a Windows NT system as they will not negotiate the proper
authentication. Please used 2.1.2c or later if you wish to connect to
Windows NT. The current version, 2.1.2d, should be used if possible.
Scott Hutton <shutton@habanero.ucs.indiana.edu> sent me the following:
Basically, NT RAS (Remote Access Services) will drop your connection
if you REJ anything critical (i.e., authentication protocol). So, the
trick was to create a mostly bogus chap-secrets file. Mine has
* "" ""
in it. This causes pppd to send a NAK rather than a REJ. With the
SPAP registry key removed, the next protocol attempted is PAP (which
is what I'm using).
Other points are to make sure that *only* TCP/IP services are enabled
in RAS (not NetBEUI nor IPX [Ed: IPX is being addressed. Until it is
installed properly, this is probably a good thing to disable as
well.]). I also had to fiddle with a couple of other registry keys to
kill timeouts (which are problematic when you're only doing TCP/IP):
HKEY_LOCAL_MACHINE\eSYSTEM\eCurrentControlSet\eServices\eRemoteAccess\eParameters
Autodisconnect: REG_DWORD: 0
and to get my routing to work correctly:
HKEY_LOCAL_MACHINE\eSYSTEM\eCurrentControlSet\eServices\eRasArp\eParameters
DisableOtherSrcPackets: REG_DWORD: 0
For completeness, the key that needs to be disabled to eliminate SPAP:
HKEY_LOCAL_MACHINE\eSYSTEM\eCurrentControlSet\eServices\eRasMan\ePPP\eSPAP
13. Other messages written to the system log
13.1. Alarm
This is not a problem. It means that a timer has expired. Timers are
a necessary part of the protocol establishment phase.
13.2. SIGHUP
The pppd process has received a HUP signal. The HUP signal is
generated by the tty software when the remote system has disconnected
the modem link. It means that the modem has put the 'telephone
receiver back on the hook', or, 'Hung UP' the connection.
The kill program may also be used to send this signal to the pppd
process.
The pppd process will terminate the link in an orderly fashion when it
receives this signal.
13.3. SIGINT
The pppd process has received an INT signal. The INT signal is
generated by the console software when you press the Ctrl-C key
combination and pppd is the foreground process.
The kill program may also be used to send this signal to the pppd
process. In fact, the recommended method to terminate the pppd link is
to send the process an INT. See the question relating to "dip -k" for
a script which will perform this task.
The pppd process will terminate the link in an orderly fashion when it
receives this signal.
13.4. Unknown protocol (c025) received!.
The remote wishes to exchange Link Quality Reporting protocol with the
Linux system. This protocol is presently not supported. This is not an
error. It is merely saying that it has received the request and will
tell the remote that "I can't do this now. Don't bother me with this!"
The Morning Star PPP package will always try to do LQR protocol. This
is normal.
13.5. The connection fails with an ioctl(TIOCSCTTY) error.
Use the ppp-2.1.2c.tar.gz package. This was a bug which was not caught
before the `a' package was released.
13.6. The connection fails with errors "ioctl(TIOCGETD): I/O error"
or "ioctl(PPPIOCSINPSIG): I/O error". What now?
Look at the boot messages when you boot the kernel. If it says "PPP
version 0.1.2" then you have an old version of the PPP.c driver.
If it says "PPP version 0.2.7" then you have the current driver,
however, it was not built with the same set of defines for the ioctl
numbers. Ensure that you have only one file called "PPP.h". It should
be located in the kernel's include/linux directory. Once you have done
this, rebuild the kernel and the pppd process.
13.7. Sometimes the messages "ioctl(PPPIOCGDEBUG): I/O error",
"ioctl(TIOCSETD): I/O error" and "ioctl(TIOCNXCL): I/O error" occur.
Why?
The remote system has disconnected the telephone. The tty drivers will
re-establish the proper tty discipline and these errors are the result
of the pppd process trying to do the same thing. These are to be
expected.
13.8. My ifconfig has strange output for PPP.
Usually the ifconfig program reports information similar to the
following:
ppp0 Link encap UNSPEC HWaddr 00-00-00-00-00-00-00 ...
inet addr 192.76.32.2 P-t-P 129.67.1.65 Mask 255.255.255.0
UP POINTOPOINT RUNNING MTU 1500 Metric 1
The information is for display purposes only. If you are using a
recent 1.2 kernel then update the nettools package with the current
one on sunacm.swan.ac.uk in the directory
/pub/Linux/networking/nettools.
13.9. The file /proc/net/dev seems to be empty
Did you just issue the command "ls -l /proc/net" and are wondering why
the size is zero? If so, this is normal. Instead, issue the command:
cat /proc/net/dev
You should not find the file empty. The size is always shown as zero,
but that is the 'proc' file system. Don't believe the size. Do the
command.
The 'more', 'less', and 'most' programs may not be used to view the
file directly. If you wish to use these programs, use it as follows:
cat /proc/net/dev | less
14. Network routing issues (using PPP as a `cheap' bridge)
14.1. Slattach and ifconfig don't work like SLIP
Do not use slattach and ifconfig with PPP. These are used for SLIP.
The pppd process does these functions at the appropriate time. These
must occur after the LCP and IPCP protocols have been exchanged.
You can not replace pppd with slattach and ifconfig. Most of the
protocol support for PPP is in the pppd process. Only the IP (and IPX
when it is completed) processing is in the kernel.
The host route to the remote system will be automatically added by
pppd. There is no option to NOT add the route. The pppd process will
terminate if the route could not be added.
The default route may or may not be added. This is controlled by the
option `defaultroute'. If you have a default route, it will not be
changed.
If you must do routing for an entire network, then put the route
command into the /etc/PPP/ip-up script. The parameters to the script
are:
$0 - name of the script (/etc/PPP/ip-up or /etc/PPP/ip-down)
$1 - name of the network device (such as ppp0)
$2 - name of the tty device (such as /dev/cua0)
$3 - speed of the tty device in Bits Per Second (such as 38400)
$4 - the local IP address in dotted decimal notation
$5 - the remote IP address in dotted decimal notation
14.2. I want the route to the network and not the route to the host.
On sunsite there is a package called devinfo.tar.gz. It contains some
useful little programs which will extract the data from the device and
to do various things with the dotted IP addresses.
The documentation is in the man pages in the file.
For example, if you want to route the entire IP domain to the remote,
the following may be used in /etc/PPP/ip-up.
Of course, if the values are not variable, then simply use the
appropriate entry in the route command.
______________________________________________________________________
# Obtain the netmask for the ppp0 (or whatever) device
NETMASK = `devinfo -d $1 -t mask`
# Obtain the IP domain (without the host address by removing the extra bits)
DOMAIN = `netmath -a $5 $NETMASK`
# Do the network route now that the IP domain is known
route -net add $DOMAIN gw $5
______________________________________________________________________
15. Other features and protocols
15.1. What about support for `demand dial'
Use the diald package. This is on sunsite in the same directory as the
PPP source, /pub/Linux/system/Network/serial.
15.2. What about `filtering'
There are no plans to put filtering into the PPP code. Run the
ipfirewall code. It is on sunsite. Help the author debug that code. It
will do the filtering that you want in a general solution.
The latest development kernels will include the patches to support
filtering. (You will still need the ipfirewall code as the kernel only
contains the patches which were in the ipfirewall code for the
kernel.) Again, filtering is a network issue and not one specifically
for PPP.
15.3. How about IPX?
The addition of support for IPX is fairly straight forward. Work is
underway to include the IPX protocol.
15.4. How about NETBIOS?
There is a netbios PPP protocol. However, your better solution would
be to use TCP/IP and the `samba' code.
Microsoft and others have used Netbios PPP protocol.
The nbfcp protocol is a public document and available from several
sources. The Netbios protocol is not a valid address family at the
present time for Linux. Until Linux supports the protocol, there is
little need to support Netbios over PPP for Linux.
15.5. I need ISDN support. Is there any?
ISDN support revolves around having a working ISDN driver. The present
design of the PPP driver does not lend itself well to the concept of a
block of data being received. This is being changed. A driver for the
Sonix interface is being developed.
15.6. How about just standard synchronous PPP?
There are small changes needed to support a serial interface which
uses synchronous communications. The redesign of the PPP driver will
help with this function as well. Kate Marika Alhola has expressed an
intrest in writing such a synchronous driver for her hardware. You
should contact her at kate@digiw.fi for further information.
16. Miscellenous
16.1. Do you have a PPP compatible mail reader?
Huh? You have the wrong group if you want MSDOS. PPP has nothing to
do with the mail user agent. All of the mail agents are compatible
with PPP.
16.2. How about a news reader?
Refer to the previous answer.