Thoughts on increasing MTUs on the internet

Sun Apr 15 01:13:14 UTC 2007

Thus spake "Bill Stewart" <nonobvious at gmail.com>
> One of my customers comments that he doesn't care about
> jumbograms of 9K or 4K - what he really wants is to be sure the
> networks support MTUs of at least 1600-1700 bytes, so that
> various combinations of IPSEC, UDP-padding, PPPoE, etc.
> don't break the real 1500-byte packets underneath.

This is a more realistic case, and support for "baby jumbos" of 2kB to 3kB 
is almost universal even on mid-range networking gear.  However, the 
problems of getting it deployed are mostly the same, except one can take the 
end nodes out of the picture in the simplest case.

OTOH, if we had a viable solution to the variable-MTU mess in the first 
place, you could just upgrade every network to the largest MTU possible and 
hosts would figure out what the PMTU was and nobody would be sending 
1500-byte packets; they'd be either something like 1400 bytes or 9000 bytes, 
depending on whether the path included segments that hadn't been upgraded 
yet...

S

Stephen Sprunk      "Those people who think they know everything
CCIE #3723         are a great annoyance to those of us who do."
K5SSS                                             --Isaac Asimov 