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

[Bruce Pinsky]

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John Neiberger wrote:

> 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. 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. 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.
> 

As I mentioned, there is no dampening mechanism on fast fall-over and peers
are dropped immediately when the next hop is lost.  If the next-hop of the
routing entries is the same as the peering address, then next-hop tracking
should be sufficient to cause the routes to flush from the RIB if
reachability is lost and next-hop tracking has a delay/dampening mechanism
built in.


- -- 
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bep

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