[c-nsp] bgp PIC Edge & neighbor shutdown

[James Bensley]

On 11 August 2017 at 10:58, Vladimir Troitskiy <ruthenate at gmail.com> wrote:
> Hi all,
>
> BGP PIC Edge on an egress PE tracks PE-CE interface and switches to backup
> path immediately when link to the CE goes down. But what if I manually
> shutdown the PE-CE eBGP session? Does it trigger immediate CEF update on
> the egress PE (ASR9k)?


Hi Vladimir,

Yes the CEF update should still happen "quickly" as is desired with
BGP PIC Edge. Assuming you have a backup route available (another
PE-CE link or via another PE) this should be already known,
pre-programmed into CEF, and marked as a backup path. Indipendant of
whether you gracefully shutdown the PE-CE link or cut it with
scissors, advantage with BGP PIC Edge is that the backup route is
already in CEF and can be promoted to active immediatly; where in the
case of graceful shutdown, the source of the RIB update that removes
the route is different (i.e. not a BGP or BFD timeout) but the process
should be the same, with the RIB then updating the FIB in memory and
then hardware CEF tables. I think the update into the RIB and from RIB
to FIB etc does not contain the "source" of the withdrawal (BGP
timeout or graceful shutdown etc.) so the process should be the same.

I haven't actually tried to time this to see if it is faster or slower
so if you get the chance I am curious to know your results!

Cheers,
James.