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SubjectRe: PPP devices given eth0 IP address upon connect.

On Sun, 7 Nov 1999, Mike A. Harris wrote:
>
> The problem is that when the PPP interface came up, the dynamic
> IP address given from the ISP end was *NOT* the IP address that
> the PPP interface used but rather PPP was using the IP address
> of the ETHERNET interface!

<snip>

> Here are the details of the problem:
>
> The local ethernet card, is configured to 10.1.1.1/24. The
> entire network is configured using a CIDR netmask of 24 bits, and
> works perfectly.
>
> When PPP is brought up using "ifup ppp0" from RedHat, the
> internet connection is established to the ISP, the debugging info
> shows the ISP's assigned IP address which is all proper. At this
> point, doing "ifconfig" shows that ppp0 is using the IP address
> for the ETHERNET interface, and NOT THE ONE GIVEN FROM THE ISP!

Try using the option 'noipdefault' on your /etc/ppp/options file and check
whether it solves the problem.

> Here is the wild part: If I reconfigure this machine to use an
> IP address of 192.168.1.40/24, and put it on another LAN that
> uses that network instead - EVERYTHING works. No change to ppp
> configuration, and it works fine. It connects to the internet,
> gets an IP, and just simply works.
>
> Change the IP address to 10.x.x.x, and reconfigure the box to use
> that IP range instead, and PPP takes over the IP address of the
> eth0 device upon connection.
>
> I have done some research on this, and I have now found that
> other people are having the problem too. Someone else has found
> that using an IP address with a "0" in it appears to cause this
> too. The IP that they are using is 192.168.0.10.

This is something I've never heard before. It might actually be a PPPd /
kernel PPP bug.

> What could POSSIBLY cause a ppp interface to take over an
> ethernet interface's IP address upon connection and IP
> negotiation?

This is something that happens when you ask pppd to use the IP address of
the first available interface on your system as the local PPP IP address
(option 'ipdefault'). If you use the option 'noipdefault', that should
_not_ happen.

Nevertheless, the specific issue of different network configuration
affecting the occurrence of the problem certainly sounds like a bug.

Regards,
Ivan


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