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? (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 --------------------------------------------------------------------
