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Re: ping-pong phenomenon with p2p links & /127 prefixes
On 2010-08-16 11:12, firstname.lastname@example.org wrote:
>> 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.
* = http://www.linux-ipv6.org/ml/usagi-users/msg02430.html