Re: ARP responses broken!

["Christopher Friesen" <cfriesen@nortelnetworks.com>]

Sampsa Ranta wrote:

> I have two interfaces that share same subnet, I call eth0 194.29.192.37
> and eth1 194.29.192.38. I have forwarding turned on, proxy arp is not
> neighter are redirects.
> 
> When I flush local neighbor table in other machine I use to observe the
> response and ping the router I get response like:
> 
> 23:38:25.278848 > arp who-has 194.29.192.38 tell 194.29.192.10 (0:50:da:82:ae:9f)
> 23:38:25.278988 < arp reply 194.29.192.38 is-at 0:1:2:dc:d2:64 (0:50:da:82:ae:9f)
> 23:38:25.279009 < arp reply 194.29.192.38 is-at 0:1:2:dc:d2:6c (0:50:da:82:ae:9f)
> 
> The second one is the valid one, but both interfaces seem to answer to the
> broadcasted packet with their own ARP addresses.

This is the default Linux behaviour.  It can be turned off by running the
following command as root:

echo 1 > /proc/sys/net/ipv4/conf/all/arp_filter

This ensures that interfaces will only respond to arp requests for IP addresses
which are configured as belonging to that particular interface.

Chris

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Chris Friesen                    | MailStop: 043/33/F10  
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