Dino, > -----Original Message----- > From: Dino Farinacci [mailto:farina...@gmail.com] > Sent: Wednesday, December 08, 2021 5:18 AM > To: Templin (US), Fred L <fred.l.temp...@boeing.com> > Cc: to...@strayalpha.com; int-area@ietf.org > Subject: Re: [Int-area] Side meeting follow-up: What exact features do we > want from the Internet? > > > > This conversation is missing some fundamental points – really the most > > important > > points – which are the minimum sizes guaranteed to work everywhere. For > > IPv6, > > the minimum MTU/MRU are 1280/1500. For IPv4, they are only 68/576 but since > > the IPv4 network supports fragmentation we can nominally designate the IPv4 > > minimum MTU as 576 also if we clear the DF bit. It means that, without > > probing > > or having some divine knowledge of paths that have not been previously > > visited, > > the ONLY sizes guaranteed to work are 1280 for IPv6 and 576 for IPv4. > > Well "ifconfig eth0 mtu 1400" makes all this work.
Good network administration cannot be guaranteed everywhere; all that can be guaranteed everywhere is 576/1280 - it says so in the specs. And, for some links, 1400 may be too big (others not big enough). > > Now take the case of Multinet where a path may traverse multiple > > concatenated > > IP networks of arbitrary IP protocol versions - remember “Catenet”? Since > > there > > may be no advanced knowledge of network IP protocol versions, the most we > > can > > absolutely and for sure count on across the entire path is 576. > > Are you talking about 4to6 and 6to4 translation? Absolutely not talking about translation - talking about concatenation and adaptation. > Then just "ifconfig eth0 mtu 1260". > > > What this gives us is not the *maximum packet size*; instead, it determines > > the > > *minimum cell size*. We know that a 576 cell will traverse all paths, so we > > never > > send a non-final cell smaller than this (which might trigger a tiny > > fragment alarm). > > But, we can certainly send packets larger than the path MTU - *much* larger > > in > > many cases. And for paths that support them, we can also send Brian’s > > jumbograms. > > I believe you are over thinking this. Just my opinion, no offense intended. Not overthinking - correctly thinking in observance of the specs. Fred > Dino _______________________________________________ Int-area mailing list Int-area@ietf.org https://www.ietf.org/mailman/listinfo/int-area
