/mcpwilling to receive this multicast group on that port. If this timer expires before a CGMP Join message is received, the port is pruned from the multicast tree for the multicast group specified in the original leave message. If it is the last port in the multicast group, it forwards the IGMP Leave message to all router ports. The router then starts the normal deletion process by sending a group-specific query. Because no responses are received, the router removes this group from the multicast routing table for that interface. It also sends a CGMP Leave message to the switch that erases the group from the static table. Fast-Leave processing ensures optimal bandwidth management for all hosts on a switched network, even when multiple multicast groups are in use simultaneously. When CGMP Leave is enabled, two entries are added to the show cam system command output, as shown below. 01-00-5e-00-00-01 01-00-5e-00-00-02 IGMP Leave uses 224.0.0.2 and IGMP Query uses 224.0.0.1. Use the following steps to troubleshoot CGMP: Due to a conflict with the HSRP, CGMP Leave processing is disabled by default. HSRP uses MAC address 01-00-5e-00-00-02, which is the same as IGMP Leave with IGMP Version 2. With CGMP Fast-Leave, all HSRP packets go to the switch CPU. Because an HSRP message is not an IGMP packet, the switch regenerates all such messages and sends them to all router ports. Routers receiving hsrp hello or hsrp peers lose connectivity. Therefore, in debugging HSRP problems, try disabling CGMP Fast-Leave.To enable CGMP Leave processing, issue the set cgmp leave enable command. 1. When CGMP Leave processing is enabled, the Catalyst 5000 family switch learns router ports through PIM-v1, HSRP, and CGMP Self-Join messages. When CGMP Leave processing is disabled, the Catalyst 5000 family switch learns router ports through CGMP Self-Join messages only. 2. CGMP does not prune multicast traffic for any IP multicast address that maps into the MAC address range of 01-00-5E-00-00-00 to 01-00-5E-00-00-FF. The reserved IP multicast addresses, in the range 224.0.0.0 to 224.0.0.255, are used to forward local IP multicast traffic in a single L3 hop. 3. CGMP and Source-Only Network A source-only network is a segment with only a source multicast and no real client. Therefore, there is a chance that no IGMP reports are generated in that segment. CGMP still needs to restrict the flooding of this source (for router use only)however. If a router detects multicast traffic on one interface with no IGMP report, it is identified as a multicast source-only network. The router generates a CGMP Join message for itself, and the switch simply adds this group (with only the router port). Configuring Cisco Routers and Switches to Enable CGMP The commands below are only valid for Catalyst 4000 and 5000 series (plus 2901, 2902, 2926, 2948G, and 4912).