Layer 3 Routing | 251Figure 17-220. Using the routing and ip address Commands to Enable RoutingIGMP ProxyThe Layer 3 package of SFTOS fully supports IGMPv3, and is backward-compatible with IGMPv1 and v2.The purpose of the IGMP Proxy feature is to enable a multicast router to learn multicast group membershipinformation and be able to forward multicast packets based upon the group membership information.IGMP Proxy is capable of functioning only in certain topologies that do not require multicast routingprotocols (i.e. DVMRP, PIM-DM, and PIM-SM) and have a tree-like topology, because no support existsfor features such as spanning tree that correct packet route loops.The proxy contains many downstream interfaces and a unique upstream interface explicitly configured. Itperforms the host side of the IGMP protocol on its upstream interface and the router side of the IGMPprotocol on its downstream interfaces.The IGMP Proxy offers a mechanism for multicast forwarding based only upon IGMP membershipinformation. The router must decide about forwarding packets on each of its interfaces based on the IGMPmembership information. The proxy creates the forwarding entries based on the membership information,then adds it to the multicast forwarding cache (MFC) in order not to make the forwarding decision forsubsequent multicast packets with the same combination of source and group. If you enable IGMP Proxyand then disable it, all the forwarding entries in the MFC are purged.As shown in Figure 17-223, use the ip igmp proxy command from the Interface Config mode to enableIGMP Proxy on the router. No multicast routing protocol should be enabled, and multicast forwardingmust be enabled on the router.Force10 #configForce10 (Config)#interface 1/0/2Force10 (Interface 1/0/2)#routingForce10 (Interface 1/0/2)#ip address 192.150.2.1 255.255.255.0Force10 (Interface 1/0/2)#exitForce10 (Config)#interface 1/0/5Force10 (Interface 1/0/5)#routingForce10 (Interface 1/0/5)#ip address 192.150.5.1 255.255.255.0Force10 (Interface 1/0/5)#exitForce10 (Config)#exit
