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Configuring IP Multicast Routing
Configuring IP Multicast Routing
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.
Note: To enable IP multicast routing, the switch must be running the IP services image.
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.
Note: If you enable PIM on multiple interfaces and most of these interfaces are not part of the outgoing interface list,
when IGMP snooping is disabled the outgoing interface might not be able to sustain line rate for multicast traffic because
of the extra, unnecessary replication.
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. Follow this procedure to enable IP
multicasting, to configure a PIM version, and to configure a PIM mode. This procedure is required.
BEFORE YOU BEGIN
Decide which PIM mode to use.
Ensure that the interface on which you are enabling multicast routing has an IP address assigned to it.
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