When enabling interdomain multicast routing, which two statements are correct? (Choose
two.)
A.
Multiprotocol BGP is used instead of PIM SM to build the intradomain and interdomain
multicast distribution trees
B.
Use MSDP to enable the RPs from different domains to exchange information about active
multicast sources
C.
MSDP SA packets are sent between the multiprotocol BGP peers
D.
Noncongruent unicast and multicast topologies can be supported using multiprotocol BGP
Explanation:
http://prakashkalsaria.wordpress.com/2010/08/11/mbgp-msdp/
MSDP In the PIM-SM model, multicast sources and receivers must register with their local
RP. Actually, the router closest to the sources or receivers registers with the RP, but the key
point to note is that the RP knows about all the sources and receivers for any particular group.
RPs in other domains have no way of knowing about sources located in other domains.
MSDP is an elegant way to solve this problem.MSDP is a mechanism that allows RPs to share information about active sources. RPs know
about the receivers in their local domain. When RPs in remote domains hear about the active
sources, they can pass on that information to their local receivers and multicast data can then
be forwarded between the domains. A useful feature of MSDP is that it allows each domain
to maintain an independent RP that does not rely on other domains, but it does enable RPs to
forward traffic between domains. PIM-SM is used to forward the traffic between the
multicast domains.
The RP in each domain establishes an MSDP peering session using a TCP connection with
the RPs in other domains or with border routers leading to the other domains. When the RP
learns about a new multicast source within its own domain (through the normal PIM register
mechanism), the RP encapsulates the first data packet in a Source-Active (SA) message and
sends the SA to all MSDP peers. The SA is forwarded by each receiving peer using a
modified RPF check, until the SA reaches every MSDP router in the interconnected
networks—theoretically the entire multicast internet. If the receiving MSDP peer is an RP,
and the RP has a (*, G) entry for the group in the SA (there is an interested receiver), the RP
creates (S, G) state for the source and joins to the shortest path tree for the source. The
encapsulated data is decapsulated and forwarded down the shared tree of that RP. When the
packet is received by the last hop router of the receiver, the last hop router also may join the
shortest path tree to the source. The MSDP speaker periodically sends SAs that include all
sources within the own domain of the RP
http://www.cisco.com/en/US/docs/ios_xr_sw/iosxr_r3.2/routing/configuration/guide/rc32bgp.html
Multiprotocol BGP
Multiprotocol BGP is an enhanced BGP that carries routing information for multiple network
layer protocols and IP multicast routes. BGP carries two sets of routes, one set for unicast
routing and one set for multicast routing.
The routes associated with multicast routing are used by the Protocol Independent Multicast
(PIM) feature to build data distribution trees.
Multiprotocol BGP is useful when you want a link dedicated to multicast traffic, perhaps to
limit which resources are used for which traffic. Multiprotocol BGP allows you to have a
unicast routing topology different from a multicast routing topology providing more control
over your network and resources.
In BGP, the only way to perform interdomain multicast routing was to use the BGP
infrastructure that was in place for unicast routing. Perhaps you want all multicast traffic
exchanged at one network access point (NAP).
If those routers were not multicast capable, or there were differing policies for which you
wanted multicast traffic to flow, multicast routing could not be supported without
multiprotocol BGP.
Note It is possible to configure BGP peers that exchange both unicast and multicast network
layer reachability information (NLRI), but you cannot connect multiprotocol BGP clouds
with a BGP cloud. That is, you cannot redistribute multiprotocol BGP routes into BGP.
