[rbridge] Pseudo-node nickname

[Radia Perlman]

2011/7/27 <hu.fangwei at zte.com.cn>

>
> The point is that there maybe two cases  that R2 loses conncetitvty to R1:
> one is R1 is died, and the other is  the link partitioning.
>
> If the link is partitioned , R2 Must not purge R1's LSP.
>
> The problem is, it's hard for R2 to know that R1 is still alive, but the
link partitioned (that was Erik's original point).  In either case (R1 is
dead, or the link partitioned), R2 will stop hearing Hellos from R1, but
R1's LSP will not have timed out.  So the possibilities are

a) wait "awhile", upon taking over as DRB, before getting a nickname for the
pseudonode.  Note that if R1's LSP hasn't expired, and R1's priority is
higher, R2 cannot legally use the nickname for the pseudonode.
b) if after "awhile" there is no path through current LSPs, to R1's LSP,
then purge *that* LSP of R1's.  (i.e., only do it once)
c) if R2 has higher nickname priority than R1, then R2 doesn't need to purge
R1's LSP.  R2 can just start using the pseudonode nickname, and if the link
is partitioned, R1 will have to acquire a new nickname for it's half of the
link.  (I think this case is safe and reasonable).
d) don't bother reusing nicknames if the DRB changes, but note that AF
changes will still be helped by this (the simplest case).

Perhaps there are other possibilities.  But I think it's safe to do c).  The
disadvantage of not doing b) is that if R1's pseudonode has higher priority
than R2's pseudonode then if R1 dies (more likely than the link partitioning
probably), R2 doesn't get to reuse the nickname.  But I'm sure people will
worry about allowing R2 to purge someone else's LSP, so only doing c)
(allowing R2 to take over the nickname if R2's pseudonode has higher
nickname priority), is reasonable.

Radia
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