[techtalk] pppd problems using kppp/RH6.0

Nils Philippsen nils at wombat.dialup.fht-esslingen.de
Sat Nov 6 17:17:01 EST 1999

On Fri, 5 Nov 1999, Becky L. Norum wrote:

> Thanks for the reply, Nils.
> I think I know what the problem is.  I have set up an ethernet card on the
> computer because we have a network printer.  BUT, to connect to the
> internet, I use a modem.  So, I think that when I try to connect to my
> provider, the provider gets confused as to what ip address to use, even
> though I have set dynamic ip addressing in the ppp settings.
> Can someone point me in the direction of how to set up two different
> network settings, one for use with the printer and one for use with the
> modem?  I've scanned a number of FAQs but maybe I'm just missing
> something.. like a keyword to look for.

The solution beforehands (well if I identified your problem correctly):
You should ensure that the options "noipdefault" and "defaultroute"
are in /etc/ppp/options, but this should not keep you from reading the
rest ("the explanation").

A typical home network setup consists of an ethernet with IPs in the
private range (192.168.0.x, 10.0.x.x and 172.something.I.forgot), i.e.
addresses which aren't routed in the internet and so anyone may use in
her/his own network without having to ask someone before, and a dialup
connection the IPs of which are assigned by a remote access server:

+---+              +---+                       +---+
|   |              |   |20.1.1.xxx +-+|   |
|PC2|              |PC1+-----------+ +=========+RAS|---> Internet
|   |              |   |           +-+         |   |
+-+-+              +-+-+          Modem        +---+
  |       |

The two networks we have are the LAN ( and the point to
point connection via the Modem to the Remote Access Server RAS
( Usually the hostname is tied to the "primary" interface vie
/etc/hosts:	pc1.mynetwork.com pc1

What recent pppds do is determine the IP address of the dialup connection
via the systems name and /etc/hosts instead of letting the RAS tell it the
dynamically assigned IP (you can check this by setting the debug option in
/etc/ppp/options and reading the logs). The option "noipdefault" tells
pppd to use the IP assigned by the RAS. The option "defaultroute" tells
the kernel to route all IP addresses where it doesn't know where to route
them (i.e. the whole world w/o your private network :-) over the ppp

If you need information how this routing thing works, check the network
administrators guide (nag, comes at least with with RHL 6.1 :-), under
/usr/doc/LDP/nag/index.html) under "A shorter index->Issues of TCP/IP
Networking->IP Routing".

The next thing would be setting up IP masquerading and/or WWW proxying if
you have more computers on your network with which you want to access the

Bye, Nils
Nils Philippsen / Vogelsangstrasse 115 / D-70197 Stuttgart / +49.711.6599405
nils at wombat.dialup.fht-esslingen.de / nils at fht-esslingen.de / nils at redhat.de
   The use of COBOL cripples the mind; its teaching should, therefore, be
   regarded as a criminal offence.                  -- Edsger W. Dijkstra

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