Cisco ASR 9000 Series Software Manual page 6

PIM-SM, PIM-SSM, and PIM-BIDIR
PIM-SM, PIM-SSM, and PIM-BIDIR
Protocl Independent Multicast (PIM) is a multicast routing protocol used to create multicast distribution trees,
which are used to forward multicast data packets. PIM is an efficient IP routing protocol that is "independent"
of a routing table, unlike other multicast protocols such as Multicast Open Shortest Path First (MOSPF) or
Distance Vector Multicast Routing Protocol (DVMRP).
Cisco IOS XR Software supports Protocol Independent Multicast in sparse mode (PIM-SM), Protocol
Independent Multicast in Source-Specific Multicast (PIM-SSM), and Protocol Independent Multicast in
Bi-directional mode (BIDIR) permitting these modes to operate on your router at the same time.
PIM-SM and PIM-SSM supports one-to-many applications by greatly simplifying the protocol mechanics for
deployment ease. Bidir PIM helps deploy emerging communication and financial applications that rely on a
many-to-many applications model. BIDIR PIM enables these applications by allowing them to easily scale
to a very large number of groups and sources by eliminating the maintenance of source state.
PIM-SM Operations
PIM in sparse mode operation is used in a multicast network when relatively few routers are involved in each
multicast and these routers do not forward multicast packets for a group, unless there is an explicit request
for the traffic.
For more information about PIM-SM, see the
PIM-SSM Operations
PIM in Source-Specific Multicast operation uses information found on source addresses for a multicast group
provided by receivers and performs source filtering on traffic.
• By default, PIM-SSM operates in the 232.0.0.0/8 multicast group range for IPv4 and ff3x::/32 (where
• If SSM is deployed in a network already configured for PIM-SM, only the last-hop routers must be
• No MSDP SA messages within the SSM range are accepted, generated, or forwarded.
PIM-Bidirectional Operations
PIM Bidirectional (BIDIR) has one shared tree from sources to RP and from RP to receivers. This is unlike
the PIM-SM, which is unidirectional by nature with multiple source trees - one per (S,G) or a shared tree from
receiver to RP and multiple SG trees from RP to sources.
Benefits of PIM BIDIR are as follows:
• As many sources for the same group use one and only state (*, G), only minimal states are required in
• No data triggered events.
• Rendezvous Point (RP) router not required. The RP address only needs to be a routable address and
Cisco ASR 9000 Series Aggregation Services Router Multicast Configuration Guide, Release 5.1.x
6
x is any valid scope) in IPv6. To configure these values, use the ssm range command.
upgraded with Cisco IOS XR Software that supports the SSM feature.
each router.
need not exist on a physical device.
Implementing Layer-3 Multicast Routing on Cisco IOS XR Software
PIM-Sparse Mode, on page 9.