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Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter24 Configuring IP Multicast Routi ng Configuring IP Multicast Routing

Leaving a Group with CGMP

When an IGMPv2 host leaves a group, it can send an IGMP leave group message to the
all-multicast-routers group (224.0.0.2). The CGMP server translates this leave group message into a
CGMP leave message and sends it to the switch.
To expedite a host on a LAN leaving a multicast group, some Layer 2 Catalyst switch software offers
the CGMP Fast-Leave feature, which allows the switch to perform IGMPv2 leave processing locally
without involving the CGMP server and accelerates the removal of unused CGMP groups. The host
sends the leave group message to the all-multicast-routers group (224.0.0.2). The Layer 2 switch
processes it and does not forward it to the CGMP server. The Layer 2 switch sends an IGMP general
query message on the port where the leave message was received to determine if there are remaining
members for the group on the port. If no response is received, the Layer 2 switch sends an IG MP leav e
message to the CGMP server, which sends a group-specific query to the multicast group to see if there
are any remaining members in the group. If there is no response, the CGMP server updates its multicast
routing table and sends a CGMP delete group message to the Layer 2 switch, which updates its routing
table.
Configuring IP Multicast Routing
This section describes how to configure IP multicast routing. It contains this co nfiguration information:
•Default Multicast Routing Configuration, page 24-13
•Multicast Routing Configuration Guidelines, page 24-14
•Configuring Basic Multicast Routing, page 24-15 (required procedure)
•Configuring a Rendezvous Point, page 24-17 (required for spare-mode or spar se-d ense -m ode
operation)
•Using Auto-RP and a BSR, page 24-27
•Monitoring the RP Mapping Information, page 24-27
•Troubleshooting PIMv1 and PIMv2 Interoperability Problems, page 24-28

Default Multicast Routing Configuration

Table24-1 show s the defa ult mu l tica st ro uti ng confi g urat ion.
Table24-1 Default Multicast Routing Configuration
Feature Default Setting
Multicast routing Disabled on all interfaces.
PIM version Version 2 (for devices running IOS Release 11.3(2)T or
later).
PIM mode No mode is defined.
PIM RP address None configured.
PIM domain border Disabled.
PIM multicast boundary None.
Candidate BSRs Disabled.