[c-nsp] iBGP and route backups

[Oliver Boehmer (oboehmer)]

[..]
> This worked great whilst both connections were on the same
> router I would get the following result for the default route.
> 
> Output of show ip bgp vpnv4 vrf Z
> 
>    Network          Next Hop            Metric LocPrf Weight Path
> Route Distinguisher: X:Y (default for vrf Z)
> *  0.0.0.0          A.B.C.D1           75             0 15735 i
> *>                  A.B.C.D2                 200      0 15735 i
> 
> 
> The problem is that when I replicate the rules and move the backup
> connection to the second router the routes that the backup router is
> learning are not being distributed to the primary router.
> That is the route distinguisher for the default route only shows the
primary connection.
> 
> Funnily enough the second router does get the default router
> fro the primary (ibgp) and from the secondary (directly connected).
>
> I have tested with another route (specific subnet) and the
> route _does_ get distributed a few seconds after the outage. Is this a
normal
> behavior of iBGP or I have some messed up configs?

This is expected. The backup router selects the "primary" default route
(as it has a higher local preference) as its best path and thus will not
announce the worse path (the one directly learnt via iBGP) to the
primary router or other iBGP peers.

When the primary is down, the backup announces its path, but stops doing
so once it learns about the better path from the primary after the
primary comes back.

	oli