[j-nsp] Resolving BGP routes using LDP tunnels

[Piotr Marecki]

On Thu, Jul 13, 2006 at 05:18:38PM +0530, Abhishek Verma wrote:
> Hi,
> 
> I have a doubt with using BGP and it recursively resolving the
> next-hops using MPLS tunnels.
> 
> R1 -- R2 -- R3
> 
> I am running LDP between R1, R2 and R3 and R1 is aware of R3's
> loopback address to mpls label binding because of LDP.
> 
> Now, i am running BGP between R1 and R3. There are some routes
> advertised by R3 to R1, with R1's NEXT_HOP.
> 
> Is it possible for R1 to use the labelled path from R1 to R3 when
> recursively resolving the next-hops for the BGP learnt routes.
> 
> I know that this happens when there exists an RSVP tunnel from R1 to
> R3. My question is that will this also work for LDP exchanged labels?
> 
> Thanks,
> Abhishek.

In general answer is YES. By default , RSVP IP address ( "to" statement ) and 
LDP LSP's towards primary /32 on loopback will be installed into router inet.3 
table . During recursive lookup for BGP NEXT_HOP , router from inet.0 and inet.3 are used , 
and if there is preference/metric draw , inet.3 routes are preffered ( which is rather unusul , 
given that RSVP has 7 and LDP 9 ). So , assuming that your configuration is pretty straightforward , 
 you will be able to use LDP LSP's out ouf the box :> ( though , if RSVP will be active in the same time , 
by default RSVP LSP will be used because of protocol preference )

Piotr Marecki