Debugging an ARP issue (no resp to ARP requests)

[Dave Tian]

Check arp_* fields in https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt <https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt>

-daveti


> On Jan 19, 2015, at 7:11 PM, Mike Krinkin <krinkin.m.u at gmail.com> wrote:
> 
> Hi,
> 
> On Mon, Jan 19, 2015 at 03:42:58PM -0800, Mandeep Sandhu wrote:
>> 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.
>> 
>> 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 192.168.2.2
>> ARPING 192.168.2.2
>> 
>> --- 192.168.2.2 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).
> 
> Have you tried to put debug prints in arp_process function?
> 
>> 
>> I don't see any drops in "netstat -s" output as well.
>> 
>> Any hints appreciated.
> 
> Just a random guess, but try to disable reverse path filtering (rp_filter).
> 
>> 
>> Thanks,
>> -mandeep
> 
>> ????
w??T?g<<???????~e

?~e??
??
>> _______________________________________________
>> Kernelnewbies mailing list
>> Kernelnewbies at kernelnewbies.org <mailto:Kernelnewbies at kernelnewbies.org>
>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies <http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies>
> 
> 
> _______________________________________________
> Kernelnewbies mailing list
> Kernelnewbies at kernelnewbies.org <mailto:Kernelnewbies at kernelnewbies.org>
> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies <http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.kernelnewbies.org/pipermail/kernelnewbies/attachments/20150119/fd6e9b19/attachment.html