Thoughts on increasing MTUs on the internet

Fri Apr 13 19:18:34 UTC 2007

-----Original Message-----
From: owner-nanog at merit.edu [mailto:owner-nanog at merit.edu] On Behalf Of
Stephen Sprunk
Sent: Friday, April 13, 2007 10:32 AM
To: Mikael Abrahamsson
Cc: North American Noise and Off-topic Gripes
Subject: Re: Thoughts on increasing MTUs on the internet

>PMTU Black Hole Detection works well in my experience, but unfortunately MS
doesn't turn it on by default, which is
> where all of the L2VPN with <1500 MTU issues come from; turn BHD on and
the problems just go away...  (And, as others
>have noted, there's better PMTUD algorithms that are designed to work
_with_ black holes, but IME they're not really
> needed)

I wish I'd had your experience. PMTU _can_ work well, but on the internet as
a whole, far too many ignorant paranoid admins block PMTU, mostly by
accident, causing all sorts of unpleasantness. Clearing DF only takes you so
far. Unless both ends are aware, and respond apppropriately to the squeeze
in the middle, you're back to square one.

Unless there were some other method of MTU Discovery implemented, depending
on something like PMTU discovery may fail just as dramatically on larger
packets as it does on 1500byte now.

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