Re: proxy arp behaviour

From: Richard B. Johnson
Date: Thu Mar 25 2004 - 12:47:05 EST

On Thu, 25 Mar 2004, Marco Berizzi wrote:

> Hello everybody,
> I would like some info about proxy arp behaviour.
> I have a firewall linux running kernel 2.4.25
> with 3 NIC. Proxy arp is enabled on two of them
> (eth0 and eth1).
> eth1 configuration is here:
> ifconfig eth1 broadcast netmask
> ip route del dev eth1
> ip route add dev eth1
> echo 1 > /proc/sys/net/ipv4/conf/eth1/proxy_arp
> Hosts connected to eth1 are all
> The linux box is now replying to arp requests
> that are sent by hosts on the eth1
> network segment. Is this because ip on eth1 is
> I think that linux should not reply to arp request
> for because of:
> ip route add dev eth1
> Is this a bug?

This problem comes up periodically and when it does there
results in a bunch of noise to show that "Linux works perfectly...",
but never with any resolution.

What needs to be answered by persons who know the network
code is how one "connects" a particular response to a
particular device.

This has become a FAQ and needs to have some written documentation

Dick Johnson
Penguin : Linux version 2.4.24 on an i686 machine (797.90 BogoMips).
Note 96.31% of all statistics are fiction.

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