[c-nsp] IOS XR Multicast RPF Check

[Oliver Boehmer (oboehmer)]

Paul Cosgrove <> wrote on Monday, March 31, 2008 10:47 AM:

> Does anyone know the algorithm used to calculate the RPF interface in
> IOS XR?
> 
> It does not appear to select the route with the lowest AD, unlike
> other IOS versions such as 12.0S.   Seems to simply prefer multicast
> routes over unicast routes (e.g. mbgp over unicast bgp) without
> performing any initial AD check.

IOS-XR has a unicast RIB (uRIB) and a multicast RIB (muRIB). By default,
only the uRIB is populated, and RPF uses these routes for RPF check. As
soon as you enable SAFI2 or ISIS/OSPF mcast topology, muRIB gets
populated with these routes, and muRIB is used for RPF check. There is
no fallback, so if you use SAFI2, you need to make sure all prefixes
which are required for RPF are also advertised via ipv4-multicast AF. 
This is different from IOS, as you've noticed already..

I recall we're working on a fallback to offer more flexibiltiy in XR as
well, don't have the ddts available right now..

	oli