Specifications

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MSDP (Multicast Source Discovery Protocol) allows multiple PIM-SM
domains to be joined. This is a way to connect multiple PIM-SM domains
together. Each PIM-SM domain uses its own independent RP(s) and does not
have to depend on RPs in other domains.
Some advantages to use MSDP are :
§ PIM-SM domains can rely on their own RPs only.
§ Domains with only receivers get data without globally advertising group
membership.
§ Global source state is not required.
An RP in a PIM-SM domain will have a MSDP peering relationship with the RPs
in other domains. The peering relationships will be made up of TCP connections
that will be used for forwarding both control information and multicast traffic itself.
Each domain will have a connection to this virtual topology. The purpose of this
topology is to have domains discover multicast sources from other domains.
MSDP doesn’t change the way that PIM-SM is used in practice, so the normal
rules of building a source-specific tree, in this case an inter-domain one, still
apply. Once the source-specific tree is built, the multicast traffic is no longer sent
over the TCP connection between RPs.
§ MSDP Mesh Groups
MSDP provides a mechanism for PIM Rendezvous Points (RPs) to learn about
active sources in remote multicast domains. Source-Active messages are sent
between MSDP peers which reach the RP so it may join a remote source tree.
Normally, when Source-Active (SA) messages are received, the active pairs are
flooded to all neighboring peers. This lets the remote RPs find out about the
source so it can join the source tree. Redundant peers and loops in the peer
topologies can cause SA message flooding to generate excessive SA messages.
JUNOS uses a hold-down mechanism to prevent the same pairs to be flooded
more often than every 50 seconds. This greatly reduces the excessive SA
messages that are sent. However, other systems use a mechanism called MSDP
Mesh Groups to limit the flooding. JUNOS supports this feature as well.
3.2.7 CIDR
CIDR stands for Classless InterDomain Routing. It supports supernetting in order
to avoid address space exhaustion. JUNOS provides CIDR-style aggregation in
BGP4. Configuration of the aggregation is achieved through syntax listing the
aggregate prefix along with the contributors to that aggregate. This configuration
has hooks into the policy mechanism to allow very general and powerful selection
of contributor prefixes to determine whether to announce an aggregate. Other
hooks into the policy allow selective contributor prefixes to be announced in
parallel with the aggregate. Similarly, route aggregation in IS-IS can be controlled
through the policy controlling leakage of Level 1 routes into Level 2.
3.2.8 Broadcast
Since the Mxxx are designed to be layer-3 routers, broadcast is not supported.
But for specific protocols like NTP or Router Discovery, you can configure the
local router in broadcast mode.
Domain 1
Domain 2
Domain 3
RP
RP
RP