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BIRD / BGP-ORR experiences?

On Wed, 15 Apr 2020 at 10:56, Deepak Jain <deepak at ai.net> wrote:


> Do we even like BGP ORR?

I like it, I think ADD-PATH and ORR are mandatory features in modern
RR infra. However proper interaction between them may not exist in
every implementation. Basically you want

a) send all ECMPable paths
b) send one backup path

This will lead to superior to full-mesh by every reasonable metric:
- smaller rib (no routes that you don't need, but all the routes you care about)
- redundancy (one iBGP down, is not customer outage)
- less state changes, less code stress

ORR is not an RFC and there are some open questions. What to reflect,
when next-hop is not in IGP? Do we hope that receiver would recurse to
the same IGP next-hop? Juniper makes this assumption, which to me is
decidedly the common case. Cisco makes no assumption and doesn't
reflect if next-hop is not in IGP, but as I understand they will fix
to the same assumption as Juniper.