[c-nsp] BGP neighbor fall-over vs BFD

[Oliver Boehmer (oboehmer)]

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>In the case I'm thinking of using it, we do all over our internal BGP
>peering to loopbacks, which are in OSPF. If we enable fallover, it sounds
>like the peer will be torn down as soon as that
> next hop is removed from the routing table.

Which is generally not something folks do in iBGP, there you would use NHT
and mark your NH as invalid. No need to tear down the session.

>One problem we have that I'm
>trying to solve is that we also have a null0 static route used for
>aggregation for the loopback addresses. This static route stops the BGP
>routes from being invalidated until the peer
> goes down because the next hop is technically still reachable, although
>via Null0. I'm pondering the use of selective next-hop filtering so that
>only /32 routes in OSPF can be used to validate next hops, but I wonder
>if 
>just enabling fallover would be better
> option. 

Nope, I would recommend enable selective address tracking (next-hop
route-map FOO), as Bruce just reasoned..

>We aren't using BFD right now. Not sure why. It seems like using
>fallover with BFD would be an excellent solution to this problem.

Until very recently, BFD has only been implemented for adjacent
neighbours. so in most cases, BFD wouldn¹t work on most iBGP sessions..

	oli