LinuxSA Mailing list archives

  From: Adam J. Sulis <asulis@range.on.ca>
  To  : linuxsa@linuxsa.org.au
  Date: Sun, 18 Jun 2000 19:39:39 -0400

PPP, Dynamic IP, and an IPCHAINS script

I hope this doesn't transmit in HTML - first email using Eudora (I think I 
have it all config'd). Sorry if it does, just let me know and I'll fix it.

I have a difficult problem which I hope you may be able to help me with. I 
have RedHat 6.2's PPPD set up to dial my ISP. My 'ppp-on' script is called 
from near the top of my init.d/firewall script, giving the ability to bring 
up the connection, wait 30 seconds to log in, then run the IPCHAINS stuff 
(which is quite large). By combining the two actions into one script, I am 
able to control them by one command, 'firewall restart'. I have a crontab 
script that checks for a valid ppp0 every five minutes. If not found, it 
restarts the firewall script and all would be fine.

Here is the glitch: Once dialed in, my ppp0 interface is given a dynamic, 
random IP from the ISP's pool. However, a few lines of code later in the 
script, my firewall script pre-sets a number of variables, one of which is 
the external interface IP, "IPADDR". I need to find a way to pass the new 
IP address to this variable on-the-fly so that IPCHAINS can pick it up and 
use it. The affected part of the script (trimmed for size) appears at the 
end of this message.

I considered doing an 'ifconfig ppp0 > /root/ifdump.txt' and then parsing 
it for the IP and redirecting it into the variable, but that seems messy. 
It would be nice if I could either export a variable right from pppd or 
chat, or somehow intercept the IP passing to the kernel and "set" the 
variable in the system. Is there perhaps a place where the IP is stored, in 
a text file somewhere?

Any suggestions to get this idea, or any other approach working would be 
most appreciated. My knowledge is growing, but I sometimes "engineer" 
myself into a corner.

Thanks in advance,

Adam Sulis
asulis@sprint.ca

Here is the code section:
<snip>
# See how we were called.
case "$1" in
   start)
         echo -n "Starting Firewalling Services: "

# ---------------------------------------------------
#  Bring up PPP
#
/etc/ppp/ppp-on
sleep 30

# Some definitions for easy maintenance.

# ------------------------------------------------------------------------
#  EDIT THESE TO SUIT YOUR SYSTEM AND ISP.

EXTERNAL_INTERFACE="ppp0"               # whichever you use
LOCAL_INTERFACE_1="eth1"                # whichever you use
LOOPBACK_INTERFACE="lo"

IPADDR="208.164.186.1"
LOCALNET_1="172.16.1.0/24"              # whatever private range you use
ANYWHERE="any/0"
</snip> 

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