HP 6125XLG R2306-HP 6125XLG Blade Switch IP Multicast Configuration Guide - Page 41

Figure 14 RPF check process IP Routing Table on Switch C Destination/Mask Interface 192.168.0.0/24 Vlan-int20 Source Switch B Receiver Vlan-int10 192.168.0.1/24 Multicast packets Switch A Vlan-int20 Vlan-int10 Receiver Switch C As shown in Figure 14, assume that unicast routes are available in the network, and no static multicast routes have been configured on Switch C. Multicast packets travel along the SPT from the multicast source to the receivers. The multicast forwarding table on Switch C contains the (S, G) entry, with VLAN-interface 20 as the incoming interface. • When VLAN-interface 20 of Switch C receives a multicast packet, because the interface is the incoming interface of the (S, G) entry, the switch forwards the packet out of all outgoing interfaces. • When VLAN-interface 10 of Switch C receives a multicast packet, because the interface is not the incoming interface of the (S, G) entry, the Switch performs an RPF check on the packet. The switch looks up its unicast routing table and finds that the outgoing interface to the source (the RPF interface) is VLAN-interface 20. It means that the (S, G) entry is correct, but the packet traveled along a wrong path. The RPF check fails and the switch discards the packet. Static multicast routes Depending on the application environment, a static multicast route can change an RPF route or create an RPF route. Changing an RPF route Typically, the topology structure of a multicast network is the same as that of a unicast network, and multicast traffic follows the same transmission path as unicast traffic does. You can configure a static multicast route for a given multicast source to change the RPF route, so that the router creates a transmission path for multicast traffic that is different from the transmission path for unicast traffic. 34