On Mon, 16 Aug 2010 11:48:41 +0200 Ole Troan <[email protected]> wrote: > Jeroen, > > >>> Unless you configure two /128's pointing to the remote side, which will > >>> then thus not be 'on-link for neighbor discovery, the little thing > >>> called the subnet anycast address will make sure that a /127 ptp simply > >>> does not work, unless you have a platform which disables the subnet > >>> anycast address of course. > >> > >> It would seem disabling the subnet anycast is fairly widespread, then. > >> I have verified the use of /127 on several hardware forwarding platforms > >> from Cisco and Juniper. /127 works just fine, and prevents the ping-pong. > >> > >> [One concrete example where /127 works: Juniper T1600 talking to Cisco > >> CRS-1 on an OC-768/STM-256 link.] > > > > It is quite wide-spread indeed, and for instance Linux used to do it > > also until a kernel update in 2003 from 2.4.20 -> 2.4.21 and they > > finally implemented subnet anycast support(*) and suddenly it all > > started breaking as for IPng.nl at the time we used /127's and everybody > > with a Linux endpoint who did an upgrade of their kernels suddenly had a > > mysterious broken configuration. > > > > Thus, do ask Cisco and Juniper and other vendors where this now 'works' > > if this intentional, or if they might finally comply to the IPv6 > > specifications one day, as then you might better watch out for this as > > it will break your network. For the vendors that have it, it might maybe > > be an idea to have a 'disable subnetanycast' command or similar so that > > one can explicitly mark a prefix that way. > > it is intentional. > there is a command to enable support for subnet-router anycast if use of that > is desired. > > is there _any_ operational experience with the use of the subnet router > anycast address? > asking the question another way. is it still a good idea, or was it ever? >
I think it's origins are likely Appletalk, where it was used for Name Binding Protocol. NBP is for resolving hostnames to autoconfigured Appletalk node addresses. It was constantly in use anytime an Appletalk network had a router. > (for 6rd we have explicitly required support of it, for discovery of the real > BR unicast address, since we're using IPv4 anycast). > > cheers, > Ole > -------------------------------------------------------------------- > IETF IPv6 working group mailing list > [email protected] > Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 > -------------------------------------------------------------------- -------------------------------------------------------------------- IETF IPv6 working group mailing list [email protected] Administrative Requests: https://www.ietf.org/mailman/listinfo/ipv6 --------------------------------------------------------------------
