Cisco WS-X6K-S2-PFC2 Software Guide - Page 685

Chapter 40 Configuring Multicast Services Understanding How Multicasting Works Understanding How RGMP Works Without RGMP, all multicast routers receive all multicast data traffic entering the switch. With RGMP, a multicast router can request not to receive multicast traffic if that router has no downstream receivers for the multicast traffic. Catalyst 6000 family switches support RGMP, which enables a switch to reduce network congestion by forwarding multicast data traffic only to those routers that are configured to receive it. Note To use RGMP, IGMP Snooping must be enabled on the switch. Protocol independent multicast (PIM) must be enabled on all routers for RGMP to work. Only PIM sparse mode is currently supported. All routers on the network must be RGMP-capable. RGMP-capable routers periodically send an RGMP hello message to the switch. The RGMP hello message tells the switch not to send multicast data to the router unless an RGMP join has also been sent to the switch from that router. When an RGMP join is sent, the router is able to receive multicast data. To learn how to set a router to receive RGMP data, see the "RGMP-Related CLI Commands" section on page 40-25. To stop receiving multicast data, a router must send an RGMP leave message to the switch. To disable RGMP on a router, the router must send an RGMP bye message to the switch. Table 40-1 provides a summary of the RGMP packet types. Table 40-1 RGMP Message Types Description Hello Bye Join Leave Action When the RGMP feature is enabled on the router, no multicast data traffic is sent to the router by the switch unless an RGMP join is specifically sent for a group. When RGMP feature is disabled on the router, all multicast data traffic will be sent to the router by the switch. Multicast data traffic for a multicast MAC address from the L3 group address G are sent to the router. These packets will have group G in the Group Address field of the RGMP packet. Multicast data traffic for the group G will not be sent to the router. These packets will have group G in the group address field of the RGMP packet. Suppressing Multicast Traffic On Gigabit Ethernet ports, you can limit the amount of bandwidth to be used for multicast traffic. Use the set port broadcast command to specify a percentage of the total bandwidth to be used for multicast traffic on Gigabit Ethernet ports. Nonreverse Path Forwarding Multicast Fast Drop In a redundant configuration where multiple routers connect to the same LAN segment, only one router forwards the multicast traffic from the source to the receivers on the outgoing interfaces. In this kind of topology, only the Protocol Independent Multicast designated forwarder (PIM-DF) forwards the data in the common VLAN, but the non-PIM-DF receives the forwarded multicast traffic. The redundant router (non-PIM-DF) must drop this traffic because it has arrived on the wrong interface and will fail the reverse path forwarding (RPF) check. Traffic that fails the RPF check is called non-RPF traffic. 78-13315-02 Catalyst 6000 Family Software Configuration Guide-Releases 6.3 and 6.4 40-5