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Configuring IP Multicast Routing
Basic IP Multicast Routing Configuration Task List
IPC-402
Cisco IOS IP Configuration Guide
PIM can operate in dense mode or sparse mode. It is possible for the router to handle both sparse groups
and dense groups at the same time.
In dense mode, a router assumes that all other routers want to forward multicast packets for a group. If
a router receives a multicast packet and has no directly connected members or PIM neighbors present, a
prune message is sent back to the source. Subsequent multicast packets are not flooded to this router on
this pruned branch. PIM builds source-based multicast distribution trees.
In sparse mode, a router assumes that other routers do not want to forward multicast packets for a group,
unless there is an explicit request for the traffic. When hosts join a multicast group, the directly
connected routers send PIM join messages toward the rendezvous point (RP). The RP keeps track of
multicast groups. Hosts that send multicast packets are registered with the RP by the first hop router of
that host. The RP then sends join messages toward the source. At this point, packets are forwarded on a
shared distribution tree. If the multicast traffic from a specific source is sufficient, the first hop router of
the host may send join messages toward the source to build a source-based distribution tree.
CGMP
CGMP is a protocol used on routers connected to Catalyst switches to perform tasks similar to those
performed by IGMP. CGMP is necessary for those Catalyst switches that cannot distinguish between IP
multicast data packets and IGMP report messages, both of which are addressed to the same group
address at the MAC level.
Basic IP Multicast Routing Configuration Task List
Basic and advanced IP multicast routing configuration tasks are described in the following sections. The
basic tasks in the first two sections are required; the tasks in the remaining sections are optional.
• Enabling IP Multicast Routing (Required)
• Enabling PIM on an Interface (Required)
• Configuring Auto-RP (Optional)
• IGMP Features Configuration Task List (Optional)
• Configuring the TTL Threshold (Optional)
• Disabling Fast Switching of IP Multicast (Optional)
• SAP Listener Support Configuration Task List (Optional)
• Enabling the Functional Address for IP Multicast over Token Ring LANs (Optional)
• Configuring PIM Version 2 (Optional)
Advanced IP Multicast Routing Configuration Task List
The advanced IP multicast routing tasks described in the following sections are optional:
• Advanced PIM Features Configuration Task List (Optional)
• Configuring an IP Multicast Static Route (Optional)
• Controlling the Transmission Rate to a Multicast Group (Optional)
• Configuring RTP Header Compression (Optional)