Running pppd under Linux

• Prerequisites:
  
  
  • linux kernel has support for TCP/IP and PPP compiled in (kernel 1.1.14 or later).
    If `cat /proc/net/dev` shows 4 or more 'ppp' devices, everything should be alright, otherwise: reconfigure and recompile your kernel (no help can be provided, we assume you know how to operate your own system)
  • `pppd` and `chat` programs must be present on your system : different linux distributions put them into different places. Newer distributions have them in /usr/sbin/ , older ones in /usr/lib/ppp/ .
  • modem has been configured to a known, working, sane configuration that does error correction, has a fixed DTE baudrate, employs hardware handshaking, connects successfully and returns CONNECT messages. Don't even try to get any further without having your modem sorted out first, or you will spend DAYS figuring out why your connection doesn't perform well, if at all!
  
  
• Procedure:
  
  • Create a shell script named 'ppp.start' , containing:
    
    #!/bin/bash
    pppd /dev/modem 38400 connect `chat -f iq.chat` mru 1500 crtscts defaultroute :
    
    (Note that the ` is the apostrophe over the TAB key !!!)
    
    pppd and chat must be in your path, otherwise specify the full path to these programs in this shell script. Replace "/dev/modem 38400" with the appropriate serial device (/dev/ttyS0 .. ttyS3 for COM 1 to COM4) and speed your modem is connected to. The last parameter is " : " this is according to the man page the <local_IP_address>:<remote_IP_address> .
    Both local (your assigned IP address) and remote IP is negotiated automatically and does not have to be given. If you have a static IP number, you might wish to make this <your assigned IP>:
    As chat -f has a parameter of "iq.chat" (here, too, you might have to give the full path, unless you call ppp.start from the directory this file is to be found in) , you must create a file of the same name with expect/reply pairs in them. Example:
    
    
  • Create a file named 'iq.chat', containing:
    
    "" ATDT17188310370 CONNECT "" host: ppp ogin: kai assword: blah
    
    The functions of these expect/reply pairs should be clear. The first expect pair is empty (""), kai is the user here, blah is his password. Make sure the permissions of this file are 600 (or similar), otherwise other users might be able to see your login/password. Use the 'chmod 600 iq.chat' command.
    
    It is strongly recommended to read the man pages for chat and pppd and the "SETUP", "README" and "README.linux" files in the pppd distribution.

  • Make sure your /etc/resolv.conf contains something like this:
    
    domain nyiq.net
    nameserver 206.102.112.2
    nameserver 204.70.128.1
    [...]
    
    You must have one or more nameservers in it, or hostnames will not resolve properly (symptom: `route` without the -n appears to be stuck, as it can't translate IP numbers to names, and you can never pull up any web pages or telnet/ftp to any place!).
    It is recommended that you run your own caching nameserver: Things will be a lot faster that way. Check the Linux Network Administrator's guide (550K gzip'd!) for details. (a LDP document, available in book form from O'Reilly and Associates, too).
    
    
  • Connecting :
    
    Executing 'ppp.start' should connect you successfully:
    
    $ ppp.start
    If you don't have the current directory in your $PATH, you will have to call it as './ppp.start' of course. The dialup progress can be monitored by doing a `tail -f /var/adm/messages` (preferably in another shell window) , if your syslog.conf is configured to log the "local2" facility to that log. If you use the 'debug' or -d option with pppd, the connection report is much more verbose: be warned that your real login/passwd appears in the log (which might be world-readable!), though.
    
    After you have connected, `route -n` should show a new 'default' route going to ppp0 and one for the terminal server on our side, also going to ppp0. At this point, everything should be working fine.
    
    
  • You might wish to create a 'ppp.down' script as well, containing the line:
    
    kill -1 `cat /var/run/ppp0.pid`
    
    Executing ppp.down will disconnect your session and delete the default route from your routing table.
    
    
  
  
• Liability by the author:
  
  None. You type it in, you burn yourself, you learn. Or else.
  
  
  
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