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Chapter 48 Configuring IP Multicast Routing
Configuring IP Multicast Routing
Sparse-mode groups in a mixed PIMv1 and PIMv2 region are possible because the Auto-RP feature in
PIMv1 interoperates with the PIMv2 RP feature. Although all PIMv2 devices can also use PIMv1, we
recommend that the RPs be upgraded to PIMv2. To ease the transition to PIMv2, we have these
recommendations:
• Use Auto-RP throughout the region.
• Configure sparse-dense mode throughout the region.
If Auto-RP is not already configured in the PIMv1 regions, configure Auto-RP. For more information,
see the “Configuring Auto-RP” section on page 48-26.

Auto-RP and BSR Configuration Guidelines

There are two approaches to using PIMv2. You can use Version 2 exclusively in your network or migrate
to Version 2 by employing a mixed PIM version environment.
• If your network is all Cisco routers and multilayer switches, you can use either Auto-RP or BSR.
• If you have non-Cisco routers in your network, you must use BSR.
• If you have Cisco PIMv1 and PIMv2 routers and multilayer switches and non-Cisco routers, you
must use both Auto-RP and BSR. If your network includes routers from other vendors, configure the
Auto-RP mapping agent and the BSR on a Cisco PIMv2 device. Ensure that no PIMv1 device is
located in the path a between the BSR and a non-Cisco PIMv2 device.
• 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 48-34.
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.
Note If you enable PIM on multiple interfaces, when most of these interfaces are not on the outgoing interface
list, and IGMP snooping is disabled, the outgoing interface might not be able to sustain line rate for
multicast traffic because of the extra replication.