... > > and the current IPv6 specification also allows PTB < 1280, > > http://tools.ietf.org/html/rfc2460#section-5 says: > > > > In response to an IPv6 packet that is sent to an IPv4 destination > > (i.e., a packet that undergoes translation from IPv6 to IPv4), the > > originating IPv6 node may receive an ICMP Packet Too Big message > > reporting a Next-Hop MTU less than 1280. In that case, the IPv6 > node > > is not required to reduce the size of subsequent packets to less > than > > 1280, but must include a Fragment header in those packets so that > the > > IPv6-to-IPv4 translating router can obtain a suitable > Identification > > value to use in resulting IPv4 fragments. Note that this means > the > > payload may have to be reduced to 1232 octets (1280 minus 40 for > the > > IPv6 header and 8 for the Fragment header), and smaller still if > > additional extension headers are used. > > Exactly. And my question was about whether the "atomic fragments" that > were found in the wild were the result of translators, or of IPv6 > networks that "violate" the standard and do not support an MTU of >= > 1280.
Dunno. I am only trying to point out that IPv6 hosts need to handle receiving ICMP packet-too-big of less than 1280, because we are going to see more stateless IPv6/IPv4 translators. If IPv6 hosts don't handle ICMP packet-too-big of less than 1280, those IPv4/IPv6 translators won't work with sub-1280 MTU IPv4 paths. And Ran has pointed out other deployments where sub-1280 MTUs are being used on IPv6. (An aside comment: I wonder if those networks can use LFI (link fragmentation and interleaving), which allows preserving the layer 3 MTU and should also provide the smaller packets needed by the layer 1 or 2 network). So, I don't think we can just wish away packet-too-big < 1280. -d -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
