[p2p-hackers] MTU in the real world

[Matthew Kaufman]

David Barrett: 
> Matthew -- Thanks for the extensive detail on the origin of 
> the 1500 number (or actually, 1492).  That helps me 
> understand and have confidence in it.

You're welcome. Before I got back into software, I used to design and
implement nationwide IP and ATM backbones, transit, and peering for ISPs, so
I know all too well what customers say when you crank the MTU down (like
when you throw a GRE tunnel into a path to try to bypass something), and
where the MTU limits come from.
 
> But even given that, have you ever tried to go above it 
> (perhaps in your work with Amicima or before)?  What kind of 
> symtoms did you experience?

The amicima MFP protocol is carefully designed to stay below the expected
MTU at all times, and in fact also worries about head-of-line blocking on
slow links.

Every time you use un-tuned NFS over UDP on a WAN link, you're sending big
(4k or 8k) packets and relying on fragmentation to make things work. It
works, but it isn't optimal.

Matthew Kaufman
matthew at matthew.at
www.amicima.com