H3C Technologies H3C S12500 Series Switches - Manual (Page 80)

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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, which differs 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.
• Response, with the IGMP Type field set to 0x1E.
Process of multicast traceroute
1. The querier sends a query to the last-hop router.
2. After receiving the query, the last-hop router turns the query packet into a request packet by adding
a response data block, which contains its interface addresses and packet statistics, to the end of
the packet. The last-hop router then forwards the request packet through unicast to the previous
hop for the given multicast source and group.
3. From the last-hop router to the multicast source, each hop adds a response data block to the end
of the request packet and unicasts it to the previous hop.
4. When the first-hop router receives the request packet, it changes the packet type to indicate a
response packet, and then sends the completed packet through unicast to the querier.
Configuration task list
Task Remarks
Enabling IP multicast routing Required.
Configuring multicast routing
and forwarding
Configuring static multicast routes Optional.
Configuring a multicast routing policy Optional.
Configuring a multicast forwarding range Optional.
Configuring the multicast forwarding table size Optional.
Configuring static multicast MAC address entries Optional.
Configuring RPF check failure processing Optional.
Tracing a multicast path Optional.
Follow these guidelines when you perform the tasks in this section: