Debugging an ARP issue (no resp to ARP requests)

Bjørn Mork bjorn at
Tue Jan 20 03:43:32 EST 2015

Mandeep Sandhu <mandeepsandhu.chd at> writes:

> Hi All,
> Please let me know if this is not the correct ML for such a question
> (or if there's a more appropriate list for it).
> I'm currently debugging an issue where Linux is not responding to ARP
> requests (testing with custom network interface h/w).
> I have 2 network interfaces which are basically interfaces on a custom
> network device sitting on the PCI bus.
> My setup looks like follows:
> xeth0 -
> xeth2 -
> xeth0/2 are the interfaces created for the custom device (via a lkm)
> Both these interfaces are on the local machine and are connected
> back-to-back on the custom device, so packets sent from one arrive on
> the other.

This won't work.  Linux will consider both addresses as local to the
host and will never respond to arp requests from any of those addresses.


You might be able to change this by tuning arp_announce/arp_ignore - But
I don't know if that changes the behaviour wrt responses to local
addresses...  See for
the meaning of these knobs.

If your main interest is to test how Linux (or your driver/hardware)
responds to ARPs, then it's definitely easiest/best to use two Linux
hosts.  This might of course be two virtual hosts running on the same
hardware if you have hardware restrictions.


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