HP 6125G HP 6125G & 6125G/XG Blade Switches IP Multicast Configuration - Page 72

multicast route on Switch C and Switch D, specifying Switch B as the RPF neighbor of Switch C and specifying Switch C as the RPF neighbor of Switch D, the receivers can receive multicast data that the multicast source sent. NOTE: • Static multicast routes only affect RPF check but cannot guide multicast forwarding. • A static multicast route is effective only on the multicast router on which it is configured, and will not be advertised throughout the network or redistributed to other routers. Multicast forwarding across unicast subnets Some networking devices might not support multicast protocols in a network. Multicast devices forward multicast traffic from a multicast source hop by hop along the forwarding tree. When the multicast traffic is forwarded to a next-hop device that does not support IP multicast, the forwarding path is blocked. In this case, you can enable multicast traffic forwarding across the unicast subnet by establishing a tunnel, such as an IPv4 over IPv4 tunnel, between the devices at both ends of the unicast subnet. For more information about tunneling, see Layer 3-IP Services Configuration Guide. Figure 25 Multicast data transmission through a tunnel Multicast router Source Switch A Unicast router Unicast router Tunnel Unicast router Unicast router Multicast router Switch B Receiver As shown in Figure 25, with a tunnel established between Switch A and Switch B, Switch A encapsulates multicast data in unicast IP packets, which unicast routers then forward to Switch B across the tunnel. Then, Switch B strips off the unicast IP header and continues to forward the multicast data down toward the receivers. If unicast static routes are configured across the tunnel, any unicast packet can be transmitted through the tunnel. If you want to dedicate this tunnel to multicast traffic delivery, you can configure only a static multicast route across the tunnel, so that only multicast packets are transmitted through this tunnel. Multicast traceroute You can use the multicast traceroute utility to trace the path that a multicast stream flows down from the first-hop router to the last-hop router. Concepts in multicast traceroute • Last-hop router-If one of the interfaces of a router connects to the subnet that contains the given destination address, and if the router can forward multicast streams from the given multicast source onto that subnet, that router is called the "last-hop router". 61