Incorrect ARP response (network)

Sanjuro sanjuroe at
Fri Nov 29 02:09:29 PST 2002


My system is an LFS 3.0 with 3.1 bootscripts, it has 2 network cards 
both Realtek 8139 10/100 MBit with support compiled into the kernel, 
with the following settings:


The problem is that when an ARP request is send (ARP is part of a 
protocol that links Ethernet and IP, the request is a broadcast asking a 
certain IP for its MAC address) the kernel returns two ARP replies, one 
with the MAC address of eth0 and one with the MAC of eth1.

It goes like this (Beta is my Linux Box, Delta my Windows 2000 Box):

Delta: ARP request for
Beta: is at <<MAC for eth0>>
Beta: is at <<MAC for eth1>>

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.

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.

Thanks in advance,


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