In your letter dated Wed, 4 Jan 2012 06:36:25 -0500 you wrote: > >On 03 Jan 2012, at 17:57 , Philip Homburg wrote: >> - For IPv6, given that the host has to do the fragmentation, >> a big minimum MTU is required. Otherwise, too much stuff >> will end up being fragmented at 576. > >There is no evidence for the claim above. When the minimum >Link MTU for IPv6 *was* set to 576, that did not happen.
RFC-2460 is from 1998. You are talking about the IPv6 network before 1998? And that resembles todays IPv6 internet in what way? >Instead, most traffic was Ethernet MTU without fragmentation, >and the next most common packet size was (Ethernet MTU - >overhead for DSL encapsulation/tunnelling). Packets at >576 were seen -- but very very infrequently -- so they >were NOT a particular burden on the end systems. Except that DNS(SEC) packets will be fragmented at the mimimum MTU (see for example the discussion in http://tools.ietf.org/html/draft-andrews-dnsext-udp-fragmentation-00) Setting the minimum MTU to 576 has to potential to cause of damage to DNSSEC. >> My guess is, that anybody who is running a links at less >> than 1280 is just going to get a lot of trouble. That applies >> both to the links you mentioned and any IPv6-to-IPv4 translators. > >Clearly it is more complex to run an IPv6 link below 1280 today >than it was when IPv6 specifications supported a 576 byte MTU. >Folks with such links tell me that it mostly works today. That's the problem with PMTU in general: it mostly works. >IPv6-IPv4 translators aren't going away. There are lots >of other reasons they get deployed -- including transition >and interoperability. Most IPv4 links are bigger than 1280. Those that aren't will cause suffering. >> Most IPv4 links are bigger than 1280. So, those translators will seem to wor >k >> in most cases. IPv4 links smaller than 1280 will just see failures that >> are quite hard to debug. > >Actually, IPv4 links with 576 byte MTUs aren't problematic. >They have worked well for ~30 years now. Except when they do. When I set the link MTU of my WAN link link to 576, VoIP stops working (over IPv4). I could either try to track down a technical person to get them to fix the problem, or I just raise the MTU. And that's how it goes in lots of cases. >RF links aren't going away, and they aren't all being >replaced by IEEE 802.11 or IEEE 802.16 either. They have had since 1998 to find a fix for the 1280 mimimum MTU problem. It is not my problem. -------------------------------------------------------------------- IETF IPv6 working group mailing list [email protected] Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
