 | | | jumbo frames issue (9000 bytes MTU) | jumbo frames issue (9000 bytes MTU) 2005-07-28 - By Tom Sightler
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On Thu, 2005-07-28 at 10:57 -0500, Lee Whatley, Contractor wrote:
> Tom Sightler wrote:
> > Yup, jumbo frame support in RHEL3 is totally broken when it comes to
> > UDP. I filed a bugzilla and support request over a year ago with
> > reproducible test cases using both NFS and simple tracepath commands,
> > including packet captures. I even went so far to figure out exactly
> > which specific patch you could back out to correct the problem (the core
> > ipsec patch in the RHEL3 tree).
> >
> > The bugzilla never went anywhere. The support request got the official
> > response of "This isn't that important so we're not going to fix it."
> >
>
> Can you forward me the bugzill id? I'll try to bug them about it too.
> Maybe of more people complain they will look into it again.
The bugzilla is 125122 but it really never went anywhere. The support
case got worked for a couple of months but eventually got stuck in the
nebulous "engineering" which, as far as I can tell at Redhat is defined
as "The group of people support claims to escalate your case to when
they decide it's a real bug but don't want to actually fix it."
The simple test case is to run tracepath, which uses UDP to determine
the actual MTU of the path between two systems. On RHEL3 it will always
report an MTU of < 1500, on every other system I have ever tested it
reports the proper MTU.
The problem appears to be with the PMTU detection. As a matter of fact
I think we were able to work around the issue in some cases by disabling
PMTU detection. Of course, this isn't a perfect solution since it will
break other things in many environments.
Later,
Tom
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