Filter
Top Products
Configuring IP Multicast Routing
Enabling IP Multicast Routing
IPC-403
Cisco IOS IP Configuration Guide
• 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:
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:
Command Purpose
Router(config)# ip multicast-routing
Enables IP multicast routing.