[c-nsp] Graceful way to terminate BGP Session

[Ian Dickinson]

Jason Lixfeld wrote:
> I can't see how the idea below saves you anything from just shutting  
> down the session.  You still incur a CPU hit when you withdraw all  
> your routes by no longer receiving them from the upstream, and the  
> internet still recalculates if you change the local preference.

Doing weight or local pref tweaks inbound etc gives you the chance to check
that everything actually has migrated to other paths - you also get to see
that the traffic on that leg has moved - and all without turning it off.  Once
you've checked this, you *know* your outbound traffic is sorted.

Doing outbound prepends or community stuff is less certain (depends on the
peer), and could cause some unneeded DFZ churn - depends on topology of course
 - but again, once you've check this, you *know* your inbound is good to go.

That certainty is the reason to do this imho.
-- 
Ian Dickinson
Senior Network Development Engineer
Pipex Communications
ian.dickinson at pipex.net
INOC-DBA: 5413*426
http://www.pipex.net

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