Debugging an ARP issue (no resp to ARP requests)

Mandeep Sandhu mandeepsandhu.chd at
Mon Jan 19 18:42:58 EST 2015

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.

I'm testing this setup by sending a single ARP pack, forced out of one
interface, for the other interface's IP.

$ sudo arping -c 1 -i xeth0

--- statistics ---
1 packets transmitted, 0 packets received, 100% unanswered (0 extra)

If I start tcpdump on the receive interface (xeth2), I see the ARP
packet arrive, but I don't see any response go out (I've attached the
pcap file for anyone interested in looking at the received packet).
The ARP packet's contents seem to be proper under wireshark.

Is there any statistics I can look at to see if the packet was dropped
by linux during ARP processing?

I've put debug stmts in the LKM, but I don't see the kernel IP layer
calling the xmit function for an ARP reply (however the xmit function
for the ARP request, from xeth0, is being called).

I don't see any drops in "netstat -s" output as well.

Any hints appreciated.

-------------- next part --------------
A non-text attachment was scrubbed...
Name: capture.log
Type: text/x-log
Size: 100 bytes
Desc: not available
Url : 

More information about the Kernelnewbies mailing list