Hi, the idea of setting a fixed 1280 MTU everywhere and for all time is silly; the maximum MTU for IPv4 is 64KB, and the maximum MTU for IPv6 is 4GB.
One item of follow-up: > Also, fragments are evil and there is no real reason to have any > fragments at all. IPv4 fragmentation works at slow speeds, but is dangerous at line rates. IPv6 fragmentation works at line rates, but is a pain point that should be avoided and/or tuned out when possible. Neither in and of themselves are "evil", however. Thanks - Fred fred.l.temp...@boeing.com > -----Original Message----- > From: ipv6-ops-bounces+fred.l.templin=boeing....@lists.cluenet.de > [mailto:ipv6-ops- > bounces+fred.l.templin=boeing....@lists.cluenet.de] On Behalf Of Jeroen Massar > Sent: Tuesday, November 11, 2014 2:06 AM > To: Vincent Bernat > Cc: IPv6 Ops list > Subject: Re: MTU = 1280 everywhere? / QUIC > > On 2014-11-11 10:55, Vincent Bernat wrote: > > ❦ 11 novembre 2014 10:42 +0100, Jeroen Massar <jer...@massar.ch> : > > > >> From: > >> https://docs.google.com/document/d/1RNHkx_VvKWyWg6Lr8SZ-saqsQx7rFV-ev2jRFUoVD34/mobilebasic > >> "UDP PACKET FRAGMENTATION" but IPv6 dos not fragment... > > > > IPv6 routers don't fragment but IPv6 hosts still do. > > Correct. But that means if you are sending 1350 bytes on a 1280 link you > are sending two packets, not one. > > As they do cool stuff like FEC in QUIC, they assume lossy networks (good > thing they think that way), but that also means that you will be sending > more data (due to FEC) and also assume you are losing packets. > > Hence, if your FEC protocol assumes that 1 packet is lost while actually > only half the packet was, you got more loss than you are anticipating. > > Knowing what the MTU is on the link, thus is a smart thing. > > Hence, why PMTUD is important. > > > Also, fragments are evil and there is no real reason to have any > fragments at all. > > Greets, > Jeroen