Dell Brocade DCX, Configuration Manual, Page: 693 / 1436

BigIron RX Series Configuration Guide 621
53-1001810-01
Configuring Multicast Source Discovery Protocol (MSDP)
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The amount of unwanted traffic in the network is reduced, but because each multicast group is
associated with a particular host, different hosts can be assigned the same multicast address for
different streams. This greatly increases the number of multicast groups that can be used in the
network. Another added benefit of SSM is that it increases security by reducing the possibility of a
rogue source disrupting the traffic from a legitimate source.
SSM defines a Short Path Tree (SPT) for multicast traffic. If SSM is enabled, the SPT is identified by
an (S,G) pair, where S is a source address and G is an SSM destination address. If the SSM protocol
is not enabled and before the SPT switchover, the multicast switch creates one (*, G) entry for the
entire multicast group, which can have many sources. The SSM SPT is on a per-source basis and
allows a client to receive multicast traffic directly from the source; that is, all joins and leaves are
source-specific. You are also able to configure a specific SSM path.
SSM is limited to multicast group addresses in the 224.0.1.0 through 239.255.255.255 address
range. If PIM Sparse is used as the multicast protocol, the SSM protocol should be enabled if you
want to filter unwanted traffic before the Shortest Path Tree protocol switchover occurs for groups
in the 232/8 range. Not configuring the SSM protocol in PIM Sparse may cause the switch or router
to leak unwanted packets with the same group, but containing undesired sources, to clients. After
SPT switch over, the leak stops and source specific multicast works correctly even without
configuring the SSM protocol.
If the SSM protocol is enabled, one (S,G) entry is created for every source of the multicast group,
even for sources with non-existent traffic. For example, if there are 1,000 sources in the group,
1,000 (S,G) entries will be created. Therefore, enabling the SSM protocol for PIM-SM requires more
software resources than leaving the protocol disabled.
Enabling SSM
To enable the SSM protocol, IGMP v3 and PIM-SM must be enabled. Enter the ssm-enable
command under the router pim level to globally enable the SSM protocol on the device.
BigIron RX(config)# ipv6 router pim
BigIron RX(config-ipv6-pim-router)# ssm-enable
Syntax: [no] ssm-enable [range <ip-address-prefix / <mask-length> ]
Enter the IP address range <ip-address-prefix / <mask-length> . The default is 232/8.
Configuring Multicast Source Discovery Protocol (MSDP)
The Multicast Source Discovery Protocol (MSDP) is used by Protocol Independent Multicast (PIM)
Sparse routers to exchange routing information for PIM Sparse multicast groups across PIM Sparse
domains. Routers running MSDP can discover PIM Sparse sources that are in other PIM Sparse
domains.
PIM Sparse routers use MSDP to register PIM Sparse multicast sources in a domain with the
Rendezvous Point (RP) for that domain.