Incorrect ARP response (network)

Dagmar d'Surreal dagmar at
Fri Nov 29 10:34:06 PST 2002

On Fri, 2002-11-29 at 04:09, Sanjuro wrote:
> So both cards are responding to an IP that is attached to only one of 
> them. This behaviour is the same in kernel 2.4.19 and 2.4.20. This is a 
> problem because depending on which one arrives first Windows send 
> network traffic to the wrong network card, which happens to be blocked 
> using iptables resulting in a loss of connection.
> My question: What could I have possible to get the kernel to do this? Is 
> it possible I compiled a strange options into the kernel? I am not 
> setting any kernel parameters at run-time or a boot time, so that can't 
> be it.

You're not going to like hearing this, but that's the default (and
considered "normal") behaviour for the 2.4.x kernels--to respond to ARP
queries for all it's addressses on any interface.

> I have tried everything else, if no-one can think of something that 
> might causing this I think I will file a bug report with the Realtek 
> kernel driver maintainer.

Don't do that.  It's not their responsibility.  They might also point
and laugh at you.  ;)

If you were running a 2.2.x kernel, this wouldn't be necessary but since
the mechanism has been changed around somewhat with 2.4.x you do need a
patch to change this behaviour (which can be more than just a little
annoying when you're trying to set up a firewall and lamers outside your
private network are leaking private network addresses that match
yours--well, annoying for _them_ anyway).  You could hop over to Google
and punch in "linux 2.4 hidden patch" or you could just cut to the chase
and go straight to  Don't
forget to read the little hidden.txt file listed on that page which
explains a little more about what's going on and what (little) you need
to do once you've applied the patch and rebuilt your kernel.

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