Cisco Systems 78-11741-02 Enabling IP Multicast Routing, Enabling PIM on an Interface, IPC-403

Configuring IP Multicast Routing

Enabling IP Multicast Routing

•Configuring IP Multicast over ATM Point-to-Multipoint Virtual Circuits (Optional)

•Configuring an IP Multicast Boundary (Optional)

•Configuring an Intermediate IP Multicast Helper (Optional)

•Storing IP Multicast Headers (Optional)

•Enabling CGMP (Optional)

•Configuring Stub IP Multicast Routing (Optional)

•Load Splitting IP Multicast Traffic Across Equal-Cost Paths Configuration Task List (Optional)

•Monitoring and Maintaining IP Multicast Routing Configuration Task List (Optional)

See the “IP Multicast Configuration Examples” later in this chapter for examples of multicast routing configurations.

To see information on IP multicast multilayer switching, refer to the Cisco IOS Switching Services Configuration Guide and Cisco IOS Switching Services Command Reference.

Enabling IP Multicast Routing

Enabling IP multicast routing allows the Cisco IOS software to forward multicast packets. To enable IP multicast routing on the router, use the following command in global configuration mode:

Command	Purpose
Router(config)# ip multicast-routing	Enables IP multicast routing.

Enabling PIM on an Interface

Enabling PIM on an interface also enables IGMP operation on that interface. An interface can be configured to be in dense mode, sparse mode, or sparse-dense mode. The mode determines how the router populates its multicast routing table and how the router forwards multicast packets it receives from its directly connected LANs. You must enable PIM in one of these modes for an interface to perform IP multicast routing.

In populating the multicast routing table, dense mode interfaces are always added to the table. Sparse mode interfaces are added to the table only when periodic join messages are received from downstream routers, or when a directly connected member is on the interface. When forwarding from a LAN, sparse mode operation occurs if an RP is known for the group. If so, the packets are encapsulated and sent toward the RP. When no RP is known, the packet is flooded in a dense mode fashion. If the multicast traffic from a specific source is sufficient, the first hop router of the receiver may send join messages toward the source to build a source-based distribution tree.

There is no default mode setting. By default, multicast routing is disabled on an interface.

Enabling Dense Mode

To configure PIM on an interface to be in dense mode, use the following command in interface configuration mode:

Cisco IOS IP Configuration Guide

IPC-403