Cisco Systems 3750E Configuring Basic Multicast Routing, Ip multicast-routing distributed, 42-12

Chapter 42 Configuring IP Multicast Routing

Configuring IP Multicast Routing

•Because bootstrap messages are sent hop-by-hop, a PIMv1 device prevents these messages from reaching all routers and multilayer switches in your network. Therefore, if your network has a PIMv1 device in it and only Cisco routers and multilayer switches, it is best to use Auto-RP.

•If you have a network that includes non-Cisco routers, configure the Auto-RP mapping agent and the BSR on a Cisco PIMv2 router or multilayer switch. Ensure that no PIMv1 device is on the path between the BSR and a non-Cisco PIMv2 router.

•If you have non-Cisco PIMv2 routers that need to interoperate with Cisco PIMv1 routers and multilayer switches, both Auto-RP and a BSR are required. We recommend that a Cisco PIMv2 device be both the Auto-RP mapping agent and the BSR. For more information, see the “Using Auto-RP and a BSR” section on page 42-24.

Configuring Basic Multicast Routing

You must enable IP multicast routing and configure the PIM version and the PIM mode. Then the software can forward multicast packets, and the switch can populate its multicast routing table.

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

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 devices or when there is a directly connected member on the interface. When forwarding from a LAN, sparse-mode operation occurs if there is an RP 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 receiver’s first-hop router might send join messages toward the source to build a source-based distribution tree.

By default, multicast routing is disabled, and there is no default mode setting. This procedure is required.

Beginning in privileged EXEC mode, follow these steps to enable IP multicasting, to configure a PIM version, and to configure a PIM mode. This procedure is required.

	Command	Purpose
Step 1
	configure terminal	Enter global configuration mode.
Step 2
	ip multicast-routing distributed	Enable IP multicast distributed switching.
Step 3
	interface interface-id	Specify the Layer 3 interface on which you want to enable multicast
		routing, and enter interface configuration mode.
		The specified interface must be one of the following:
		• A routed port: a physical port that has been configured as a Layer 3
		port by entering the no switchport interface configuration
		command.
		• An SVI: a VLAN interface created by using the interface vlan
		vlan-idglobal configuration command.
		These interfaces must have IP addresses assigned to them. For more
		information, see the “Configuring Layer 3 Interfaces” section on
		page 11-31.

	Catalyst 3750-E and 3560-E Switch Software Configuration Guide
42-12	OL-9775-02