In order to configure two routers as anycast RPs, which of these requirements, af a minimum,
must be satisfied?
A.
Multicast Source Discovery Protocol mesh-groups must be configured between the two anycast
RPs.
B.
The RPs must be within the same IGP domain.
C.
Multicast Source Discovery Protocol must be configured between the two anycast RPs.
D.
The two anycast RPs must be IBGP peers.
Explanation:
Multicast Source Discovery Protocol (MSDP) is a mechanism to connect multiple PIM sparsemode (SM) domains. MSDP allows multicast sources for a group to be known to all rendezvous
point(s) (RPs) in different domains. Each PIM-SM domain uses its own RPs and need not depend
on RPs in other domains. An RP runs MSDP over TCP to discover multicast sources in other
domains. An RP in a PIM-SM domain has an MSDP peering relationship with MSDP-enabled
routers in another domain. The peering relationship occurs over a TCP connection, where
primarily a list of sources sending to multicast groups is exchanged. The TCP connections
between RPs are achieved by the underlying routing system. The receiving RP uses the source
lists to establish a source path. The purpose of this topology is to have domains discover multicast
sources in other domains. If the multicast sources are of interest to a domain that has
receivers, multicast data is delivered over the normal, source-tree building mechanism in PIM-SM.
MSDP is also used to announce sources sending to a group. These announcements must
originate at the domain’s RP.
MSDP depends heavily on (M)BGP for interdomain operation. It is recommended that you run
MSDP in RPs in your domain that are RPs for sources sending to global groups to be announced
to the internet.
Each MSDP peer receives and forwards the SA message away from the originating RP to achieve
“peer- RPF flooding.” The concept of peer-RPF flooding is with respect to forwarding SA
messages. The router examines the BGP or MBGP routing table to determine which peer is the
next hop toward the originating RP of the SA message. Such a peer is called an “RPF peer”
(Reverse-Path Forwarding peer). The router forwards the message to all MSDP peers other than
the RPF peer.
If the MSDP peer receives the same SA message from a non-RPF peer toward the originating RP,
it drops the message. Otherwise, it forwards the message on to all its MSDP peers.
When an RP for a domain receives an SA message from an MSDP peer, it determines if it has any
group members interested in the group the SA message describes. If the (*, G) entry exists with a
nonempty outgoing interface list, the domain is interested in the group, and the RP triggers an (S,
G) join toward the source.