jumbo frames issue (9000 bytes MTU)

Sean Dilda agrajag at dragaera.net
Thu Jul 28 15:35:50 CDT 2005

wolf2k5 wrote:
> Hi,
> I enabled jumbo frames (9000 bytes MTU) on two Dell PowerEdge 1850
> servers running Red Hat Enterprise Linux 3 ES Update 5 x86_64 using
> the following commands:
> ifconfig eth1 mtu 9000
> service network restart
> After the MTU change, I was able to transfer (scp) very small files
> between the servers, ping also worked fine, but when trying to
> transfer bigger files, the copy process got stuck.
> Also, the NFS mounts didn't work anymore.
> I reverted the MTU change and all got back to work as before.

Did you also enable jumbo frames on the other hosts on the switch?  The 
symptoms you report sound like what I see if I have one box on a switch 
with jumbo frames on, and one without.  That's the tricky thing about 
jumbo frames, you can't just turn it on for one host.  You have to turn 
it on for every host on that switch, or things just won't work right.

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