MBGP/MSDP implementation

wakhan123 · ‎05-03-2010

Hello All,

I am trying to configure MBGP / MSDP peer b/w NREN router and our RP. Can you please tell that do i have to enable MBGP on our Edge Router and then run iMBGP b/w edge router and Multi-RP or i can directly create MBGP/MSDP peer b/w NREN and RP. Which solution is better?? And what is the procedure and requirements ?

  I was reading the MSDP RFC and i found below paragraph, which match to our scernario.

   For example, in the diagram below, if customer NREN router is MBGP
   peering with the EDGE router and if NREN is MSDP peering with the RP
   router, then EDGE and RP must be in the same AS (or must appear, to
   AS1, to be from the same AS in the event that private AS numbers are
   deployed).  The MSDP peer with the highest IP address will be chosen
   as the MSDP RPF peer.  NREN must also have the MSDP peer address of RP
   in its MBGP table.

         +---+      +----+    +--+
         |NREN|-----|EDGE|----|RP|
         +---+      +----+    +--+
         AS1          AS2      AS2

   From RP's perspective, AS1 (NREN) is the MBGP next AS in the best path
   towards the originating RP.  As long as AS1 is the next AS (or
   closest) in the best path towards the originating RP, RPF will
   succeed on SAs arriving from R1.

Regards,

Giuseppe Larosa · ‎05-03-2010

Hello Wakhan123,

in inter-AS multicast scenarios with MSDP and MP BGP you should follow the following guidelines:

MSDP sessions are configured between routers acting as Rendez-vous points in your AS and in peer AS in order to exchange information about possible multicast sources.

MP BGP is needed to pass the RPF check so you need to run an eBGP session of type MP BGP at the border link. Your edge router needs to peer with your RP in address-family ipv4 multicast.

A design document (using an older syntax) is present at the following link:

http://www.cisco.com/en/US/docs/ios/solutions_docs/ip_multicast/Phase_1/mcst_p1.html#wp1057566

Hope to help

Giuseppe

wakhan123 · ‎05-04-2010

Hello Giuseppe,

After reading your reply, i have designed this topoloy, is it OK? Why we need to i-MBGP peer b/w our RP and our edge router ?

And do MSDP peer will be configure on loopback addresses? because i was reading in multicast implementation guide that "For MSDP peering sessions, we use the same IP address that was used for the BGP peering session", if this is the requirement then how it will be possible in our scenario.

Regards,

Waqas Ahmed

Giuseppe Larosa · ‎05-04-2010

Hello Wakhan123,

>> After reading your reply, i have designed this topoloy, is it OK? Why we need to i-MBGP peer b/w our RP and our edge router ?

the topology is fine. You need to use both the eBGP session and the iBGP session because a multicast flow originated in other AS can be accepted only if it passes the Reverse Path Forwarding check (RPF check). MSDP alone is not enough to pass this test and BGP provides the routes in order to pass RPF check.

Otherwise you could learn about multicast traffic sources in other AS in MSDP but traffic originated by those sources could not flow into your AS.

You can use the same loopback address as BGP and MSDP endpoint, it can also be used as RP ip address (unless in Anycast RP)

Hope to help

Giuseppe

wakhan123 · ‎05-04-2010

Hello Giuseppe,

Thanks for your Reply.

One more question.Do we have to run iMBGP peer with our other Core Routers too ? like b/w edge router and core1 and core 2 ? or iMBGP peer with RP is enough!

Regards,

Waqas Ahmed

Giuseppe Larosa · ‎05-04-2010

Hello Waqas Ahmed,

RPF check of the multicast source is performed by each multicast routing enabled router in your AS, so, as explained in the design document I had linked, you need to extend MP BGP over all iBGP peers.

To be noted you can use BGP route reflector servers to solve the full mesh problem for address family ipv4 multicast as we do for other address families.

Redistributing eBGP routes into IGP at border router is the only alternate solution, but it is not recommended.

Hope to help

Giuseppe