In your letter dated Wed, 4 Jan 2012 08:46:31 -0500 you wrote: >On 04 Jan 2012, at 07:17 , Philip Homburg wrote: >> RFC-2460 is from 1998. You are talking about the IPv6 network >> before 1998? And that resembles todays IPv6 internet in what way? > >The network layer is largely the same. Routing >is largely the same, except that table sizes >always seem to increase. Certainly transport >protocols are largely the same. We now have SCTP, >although it seems not yet widely deployed.
Yes, but PMTU failures are not a protocol issue. Is it is an operational issue. So when the IPv6 network is just a bunch of techies who are connected by tunnels, you expect PMTU to sort of work. By the time the internet is big is enough that some routers just send ICMPs with link local source and nobody notices, then PMTU starts to break down. >The bulk of the Internet continues to use IPv4 today, >and probably will for the next decade. The IPv4 >specifications and widely deployed IPv4 >implementations both support a 576 byte Link MTU. > >So DNSsec will need to work over 576 byte links >just to be deployable in the bulk of the deployed >Internet. That might be awkward, or sub-optimal, >but it is not a recent development. I'm sure you know about the small difference between IPv4 and IPv6 when it comes to fragmentation. For IPv4, if a DNS server need to send a, say, 1000 octet reply then it can just send it. If necessary, routers on the way will fragment the reply. Your 576 octet link will have no effect on me. On the other hand, for IPv6, a DNS server will have to fragment at the lowest common denominator. So making the minimum link MTU 576, will cause a lot more IPv6 fragments then you would get for IPv4. And makes IPv6 quite a bit worse than IPv4. If you follow this to the logical conclusion, then with the IPv6-IPv4 translators, a DNS server has to add a fragmentation header to every DNS reply, even the small ones. Wasting an enormous amount of processing power in the years to come. >> When I set the link MTU of my WAN link to 576, >> VoIP stops working (over IPv4). > >Curious. I know of several deployments of VoIP >over small MTU links. They work fine using standard >off-the-shelf IETF protocols for VoIP (e.g. SIP, RTP). >So it isn't a protocol problem. It is not a protocol problem. My guess is that this is some kind of firewall that drops fragmented packets. But can't be sure. >> They have had since 1998 to find a fix for the >> 1280 mimimum MTU problem. It is not my problem. > >The Link MTU minimum size is the IETF's problem, >because the IETF is trying to support the whole >globe's networking needs. IPv4 does so today. >It would be sad if IPv6 could not do so. Well, you can always tunnel IPv6 over IPv4. Problem solved :-) -------------------------------------------------------------------- IETF IPv6 working group mailing list ipv6@ietf.org Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
