Re: [Idr] I-D Action: draft-ietf-idr-bgp-fwd-rr-02.txt

[Robert Raszuk <[e-mail]>]

Hi Igor,


> This is crucial to my point. The local "repair" action is really not a
>> repair. When you loose your sessions on primary ABR1 to region-2, or you
>> get withdraws etc ...) you need to re-run local (on said ABR1) best path as
>> there is no other trigger to simply activate bulk switchover in data plane
>> to suddenly go to ABR2. This is the key.
>>
> [IM] I see at least three such triggers.
>

Ahhh see the crux of the matter is that none of those listed below is
applicable to support bulk data plane switchover to back ABR :(

An outgoing Region2-faced interface failure.
>

When you loose interface and ABR is (and should be) connected via at least
two interfaces to each region your IBGP sessions are intact.

And even if this is single interface and you invent new harmful knob to
invalidate IBGP sessions when interface X goes down (this is common
practice on directly connected EBGP sessions only) you still have zoo of
prefixes received over those IBGP sessions and each may have been
advertised with different label.

So you still need to run full best path and pick new (now backup path) on a
per prefix basis and install one by one in RIB/FIB/LFIB.


> An IGP event in Region 2 with a remote ASBR failure.
>

Ok you can invalidate a remote next hop. Sure. But that means as you have
observed already that each route may be incoming with different label so
you need prefix by prefix pick alternative label and install it in
RIB/FIB/LFIB locally.



> An RSVP event of underlying Region 2's LSP failure.
>

Whow ... now we see a soft state protocol through into this mix.  And when
an RSVP-TE LSP to remote next hop in region-2 goes down you want to
consider this a trigger to invalidate given next hop ? Ok but we are back
to #2 above. Still one by one ...


> All of them describe some group of prefixes and can influence the
> switchover to their backups.
>

That would be true for vanilla IPv4/\Pv6 SAFI 1. Not for SAFI 4 or SAFI 76.

Cheers,
R.