On 01/02/2012 08:02 PM, Dan Wing wrote: >> Well, as long as communication does work without requiring the sending >> node to fragment packets to < 1280, the standard is not being "broken". >> >> In the scenario I was describing, the underlying reason for receiving >> an >> ICMPv6 PTB <1280 might be a network that doesn't support an MTU >= 1280 >> (and hence, that violates the standard). > > It is not a violation to send PTB of less then 1280. Never has been, > even going back to RFC1883 when the IPv6 minimum MTU was 576, > http://tools.ietf.org/html/rfc1883#section-5 says:
The violation would be that of not support an MTU >= 1280, rather than the sending of the ICMPv6 PTB. > 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. Thanks, -- Fernando Gont SI6 Networks e-mail: fg...@si6networks.com PGP Fingerprint: 6666 31C6 D484 63B2 8FB1 E3C4 AE25 0D55 1D4E 7492 -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
