Operation Manual – MulticastH3C S5500-EI Series Ethernet SwitchesChapter 9 Multicast Routing andForwarding Configuration9-5unicast RPF route and the optimal multicast static route respectively from the routingtables, and uses one of them as the RPF route after comparison.Figure 9-2 Multicast static routeAs shown in Figure 9-2, when no multicast static route is configured, Switch C’s RPFneighbor on the path back to Source is Switch A and the multicast information fromSource travels along the path from Switch A to Switch C, which is the unicast routebetween the two switches; with a static route configured on Switch C and Switch B asSwitch C’s RPF neighbor on the path back to Source, the multicast information fromSource travels from Switch A to Switch B and then to Switch C.9.1.4 Multicast TracerouteThe multicast traceroute utility is used to trace the path that a multicast stream flowsdown from the multicast source to the last-hop router.I. Concepts in multicast traceroute1) Last-hop router: If a router has one of its interfaces connecting to the subnet thegiven destination address is on, and if the router is able to forward multicaststreams from the given multicast source onto that subnet, that router is calledlast-hop router.2) First-hop router: the router that directly connects to the multicast source.3) Querier: the router requesting the multicast traceroute.II. Introduction to multicast traceroute packetsA multicast traceroute packet is a special IGMP packet, which differs from commonIGMP packets in that its IGMP Type field is set to 0x1F or 0x1E and that its destinationIP address is a unicast address. There are three types of multicast traceroute packets:z Query, with the IGMP Type field set to 0x1F,
