NFS not negotiating MTU correctly?

NFS not negotiating MTU correctly?

[Chris Worley]

I don't know why this is an NFS specific problem (I'd think this would
be part of IP)...

I run 9K MTU's on all my NFS servers and most of my clients.  Great
performance (the servers are also channel bonded... but that's
irrelevant).

Clients that can't do 9K MTU's work with the 9K MTU systems for all
sorts of network tasks, except NFS.

To get NFS to work, I either have to use NFS over TCP, or set my w/rsize
below 1500 bytes.  Both cause performance problems.

In grilling my switch vendor, they assure me that it's the client &
servers job to negotiate properly fragmented packets based on the lessor
MTU.

Chris



-------------------------------------------------------
This SF.Net email is sponsored by: Oracle 10g
Get certified on the hottest thing ever to hit the market... Oracle 10g. 
Take an Oracle 10g class now, and we'll give you the exam FREE.
http://ads.osdn.com/?ad_id=3149&alloc_id=8166&op=click
_______________________________________________
NFS maillist  -  NFS@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/nfs

Re: NFS not negotiating MTU correctly?

[Trond Myklebust]

P=E5 ty , 25/05/2004 klokka 09:18, skreiv Chris Worley:

> In grilling my switch vendor, they assure me that it's the client &
> servers job to negotiate properly fragmented packets based on the lessor
> MTU.

That sounds like a piss-poor switch to me. AFAIK all routers are
supposed to automatically fragment datagrams when forwarding between
networks that have a different MTU. Automatic MTU discovery is not part
of the IP protocol (although methods for doing so under certain
circumstances do exist).

In any case, dealing with MTUs is entirely the networking layer's job.
NFS just deals with sockets. I suggest that you check that the
ip_no_pmtu_disc sysctl is set correctly, and then check with the Linux
networking mailing list (netdev@oss.sgi.com) if there are further
problems.

Cheers,
  Trond


-------------------------------------------------------
This SF.Net email is sponsored by: Oracle 10g
Get certified on the hottest thing ever to hit the market... Oracle 10g. 
Take an Oracle 10g class now, and we'll give you the exam FREE.
http://ads.osdn.com/?ad_id=3149&alloc_id=8166&op=click
_______________________________________________
NFS maillist  -  NFS@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/nfs