Debugging an ARP issue (no resp to ARP requests)

[Bjørn Mork]

Mandeep Sandhu <mandeepsandhu.chd at gmail.com> 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 - 192.168.2.1
> xeth2 - 192.168.2.2
>
> 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.

See http://en.wikipedia.org/wiki/Host_model

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
https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt 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.


Bjørn