In message <[email protected]>, Roland Dobbins wri tes: > > On Sep 13, 2014, at 6:58 PM, Mark Andrews <[email protected]> wrote: > > > But do force IPv6 to fragment at 1280. This advoids PMTUD. > > Personally, I'd rather see pressure on networks to do The Right Thing in te= > rms of ICMPv6 . . . > > ;>
PMTUD for DNS/UDP is a pain in the butt. Even if you get a PTB message you do not have the data to resend the packet with a different fragmentation point. This is why the precurser to IPV6_USE_MIN_MTU was invented back in the 1990's. Some data streams work with PMTUD and some don't. This is also the same reason that with IPv4 that PMTUD is only supposed to be on by default for TCP and not for anything else. Named also tries to disable PMTUD for IPv4 when the stack mis-implements PMTUD. DNS/TCP doesn't have this issue but there is no real benefit, except maybe for large zone transfers, in trying to find the biggest path MTU when 1280 is quite acceptable for DNS/TCP. The occasional extra packet on a DNS/TCP transaction is not harmful in the great scheme of things. This isn't about getting the network to do the right thing as much as it should. It is about PMTUD being a bad fit for DNS. Mark > ---------------------------------------------------------------------- > Roland Dobbins <[email protected]> // <http://www.arbornetworks.com> > > Equo ne credite, Teucri. > > -- Laoco=F6n > > > _______________________________________________ > dns-operations mailing list > [email protected] > https://lists.dns-oarc.net/mailman/listinfo/dns-operations > dns-jobs mailing list > https://lists.dns-oarc.net/mailman/listinfo/dns-jobs -- Mark Andrews, ISC 1 Seymour St., Dundas Valley, NSW 2117, Australia PHONE: +61 2 9871 4742 INTERNET: [email protected] _______________________________________________ dns-operations mailing list [email protected] https://lists.dns-oarc.net/mailman/listinfo/dns-operations dns-jobs mailing list https://lists.dns-oarc.net/mailman/listinfo/dns-jobs
