Hi, Brian, On 08/19/2014 09:09 PM, Brian E Carpenter wrote: >> On 08/19/2014 07:58 PM, Brian E Carpenter wrote: >>>> It does seem kind of silly that we say "you must support MTU >= 1280 to run >>>> IPv6" and then allow PTB packets with an MTU < 1280. Any reason we can't >>>> simply say that PTB packets < 1280 are invalid? >>> Because of SIIT, that is equivalent to saying that the minimum IPv4 >>> MTU is now 1260. That might be a discussion worth having, but 576 has >>> been around for a long time. >> >> Not sure what you meant about 576... that we can assume that to be a >> minmum MTU, > > Yes, that hasn't changed since RFC 791
Not really. For v4, 576 is the "minimum reassembly buffer size" (you're guaranteed to the remote host can reassemble a datagram of that size), not the minimum MTU. The IPv4 minimum MTU is actually 68 bytes. While working on RFC5927, I recall that at least OpenBSD enforced a lower limit as low as (around) 296 bytes, since that accommodated some radio links that were known to be in use at the time... > Maybe we consider it acceptable that SIIT will break on paths that > include a shorter-than-Ethernet link MTU. But we need to make that > statement explicit. Or just update SIIT along with deprecating the generation of atomic fragments. -- At the end of the day, not that long ago there were at least a handful of implementations that didn't react to ICMPv6 PTB<1280 as required by RFC2460. Some we might already have scenarios in which the SIIT device expects the host to generate atomic fragments, but it doesn't. Thanks! Best regards, -- Fernando Gont SI6 Networks e-mail: [email protected] PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492 _______________________________________________ OPSEC mailing list [email protected] https://www.ietf.org/mailman/listinfo/opsec
