Specifications

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Cisco MWR 2941 Mobile Wireless Edge Router Software Configuration Guide, Release 12.2(33)MRB
OL-21227-02
Chapter 1 Cisco MWR 2941 Router Overview
Features
For more information about sparse mode, see the Cisco IOS IP Multicast Configuration Guide, Release
12.2SR.
PIM Source Specific Multicast Mode
SSM is a datagram delivery model that best supports one-to-many applications, also known as broadcast
applications. SSM is a core networking technology for the Cisco implementation of IP multicast
solutions targeted for audio and video broadcast application environments and is described in RFC 3569.
The following two Cisco IOS components together support the implementation of SSM:
• Protocol Independent Multicast source-specific mode (PIM-SSM)
• Internet Group Management Protocol Version 3 (IGMPv3)
Protocol Independent Multicast (PIM) SSM, or PIM-SSM, is the routing protocol that supports the
implementation of SSM and is derived from PIM sparse mode (PIM-SM). IGMP is the Internet
Engineering Task Force (IETF) standards track protocol used for hosts to signal multicast group
membership to routers. IGMP Version 3 supports source filtering, which is required for SSM. For SSM
to run with IGMPv3, SSM must be supported in the Cisco IOS router, the host where the application is
running, and the application itself.
For more information about SSM, see the Cisco IOS IP Multicast Configuration Guide, Release 12.2SR.
Rendezvous Points
A rendezvous point (RP) is a role that a router performs when operating in PIM-SM mode. An RP is
required only in networks running PIM-SM. In PIM-SM, only network segments with active receivers
that have explicitly requested multicast data will be forwarded the traffic. This method of delivering
multicast data is in contrast to the PIM dense mode (PIM-DM) model. In PIM-DM, multicast traffic is
initially flooded to all segments of the network. Routers that have no downstream neighbors or directly
connected receivers prune back the unwanted traffic.
An RP acts as the meeting place for sources and receivers of multicast data. In a PIM-SM network,
sources must send their traffic to the RP. This traffic is then forwarded to receivers down a shared
distribution tree. By default, when the first hop router of the receiver learns about the source, it will send
a Join message directly to the source, creating a source-based distribution tree from the source to the
receiver. This source tree does not include the RP unless the RP is located within the shortest path
between the source and receiver.
In most cases, the placement of the RP in the network is not a complex decision. By default, the RP is
needed only to start new sessions with sources and receivers. Consequently, the RP experiences little
overhead from traffic flow or processing. In PIM version 2, the RP performs less processing than in PIM
version 1 because sources must only periodically register with the RP to create state.
Auto-RP
In the first version of PIM-SM, all leaf routers (routers directly connected to sources or receivers) were
required to be manually configured with the IP address of the RP. This type of configuration is also
known as static RP configuration. Configuring static RPs is relatively easy in a small network, but it can
be laborious in a large, complex network.
Following the introduction of PIM-SM version 1, Cisco implemented a version of PIM-SM with the
Auto-RP feature. Auto-RP automates the distribution of group-to-RP mappings in a PIM network.
Auto-RP has the following benefits:
• Configuring the use of multiple RPs within a network to serve different groups is easy.