re0 checksum offloading issue (Re: nfs server issues)

Jon Noack noackjr at
Fri Apr 2 18:20:18 PST 2004

On 4/2/2004 6:44 PM, Sean McNeil wrote:
> On Fri, 2004-04-02 at 16:07, Dan Nelson wrote:
>>In the last episode (Apr 02), Sean McNeil said:
>>>On Fri, 2004-04-02 at 13:57, Dan Nelson wrote:
>>>>In the last episode (Apr 02), Sean McNeil said:
>>>>>OK, here is a tcpdump.  It is confusing. It looks like after the
>>>>>first fragment is received it is looking up some bazaar IP
>>>>>13:02:57.566952 > 136 readdir fh 1002,54097/7890231 4096 bytes @ 0x000000000 (DF)
>>>>>13:02:57.567266 > reply ok 1472 readdir (frag 1645:1480 at 0+)
>>>>>13:02:57.567268 > (frag 1645:4 at 1480)
>>>>Weird.  Is this at the server or the client?
>>>This is a client-side dump.  Both server and client have MTU of 1500.
>>>Server side says:
>>>15:37:44.292564 IP > 136 readdir fh 1002,54097/7890231 4096 bytes @ 0x0
>>>15:37:44.292705 IP > reply ok 1472 readdir
>>>15:37:44.292711 IP > udp
>>>Is there something in a packet that tells rpc/nfs to reassemble with
>>>something other than the source/destination info?
>>Neither RPC or NFS are involved with fragmentation.  That's all done at
>>the UDP level.  I wonder if it's a NIC problem.  Can you try a
>>different card (maybe even a different brand of card if possible)? 
>>another interesting test would be to get a hub and a 3rd machine, then
>>do dumps with the hub on the server's port, and then the client's port. 
>>If you get garbled frags in both places, I'd lean toward a NIC problem
>>on the server.  If your card supports checksum offloading, try
>>disabling it (ifconfig xx0 -rxcsum -txcsum).
> Bingo!  It looks like a problem with checksum offloading:
> 	ifconfig re0 -rxcsum -txcsum
> and now it no longer hangs.  Good call!  The NIC in question is:
> re0: <RealTek 8110S Single-chip Gigabit Ethernet> port 0xa400-0xa4ff mem
> 0xdf004000-0xdf0040ff irq 12 at device 11.0 on pci1
> The extremely odd thing is http, ldap, samba, and many other services
> that go both to the box and are sent out via nat all work fine.  nfs is
> the only protocol I've seen that has an issue.
> I am happy now :)
> Cheers,
> Sean

I'm copying you on this in case you (as the original author) can see 
anything wrong with the driver checksum offloading.

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