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Software Configuration Guide—Release 12.2(25)EW
OL-6696-01
Chapter 25 Understanding and Configuring IP Multicast
Configuring IP Multicast Routing
Note When PIM-SM routing is in use, the MFIB route might include an interface like in this example:
PimTunnel [1.2.3.4]. This is a virtual interface that the MFIB subsystem creates to indicate that packets
are being tunnelled to the specified destination address. A PimTunnel interface cannot be displayed with
the normal show interface command.
S/M, 224/4
An (S/M, 224/4) entry is created in the MFIB for every multicast-enabled interface. This entry ensures
that all packets sent by directly connected neighbors can be Register-encapsulated to the PIM-SM RP.
Typically, only a small number of packets would be forwarded using the (S/M,224/4) route, until the
(S,G) route is established by PIM-SM.
For example, on an interface with IP address 10.0.0.1 and netmask 255.0.0.0, a route would be created
matching all IP multicast packets in which the source address is anything in the class A network 10. This
route can be written in conventional subnet/masklength notation as (10/8,224/4). If an interface has
multiple assigned IP addresses, then one route is created for each such IP address.
Unsupported Features
The following IP multicast features are not supported in this release:
• Controlling the transmission rate to a multicast group
• Load splitting IP multicast traffic across equal-cost paths
Configuring IP Multicast Routing
The following sections describe IP multicast routing configuration tasks:
• Default Configuration in IP MUlticast Routing, page 25-13
• Enabling IP Multicast Routing, page 25-13
• Enabling PIM on an Interface, page 25-13
For more detailed information on IP multicast routing, such as Auto-RP, PIM Version 2, and IP multicast
static routes, refer to the Cisco IOS IP and IP Routing Configuration Guide, Release 12.2.
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