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Figure 29 Multicast data transmission through a tunnel

As shown in Figure 29, with 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".

• First-hop router—The router that directly connects to the multicast source is called the "first-hop

router".

• Querier—The router that sends multicast traceroute requests is called the "querier".

Introduction to multicast traceroute packets

A multicast traceroute packet is a special IGMP packet that is different from common IGMP packets in

that its IGMP Type field is set to 0x1F or 0x1E and its destination IP address is a unicast address. The

following types of multicast traceroute packets are available:

• Query, with the IGMP Type field set to 0x1F,

• Request, with the IGMP Type field set to 0x1F, and

• Response, with the IGMP Type field set to 0x1E.

Unicast router

Multicast router

Switch ASource ReceiverSwitch B

Tunnel

H3C S5500-EI User Manual

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