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• 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.
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. It 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. Then, it 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
Tracing a multicast path Optional
IMPORTANT:
IP multicast does not support secondary IP address segments. Namely, multicast can be routed and
forwarded only through primary IP addresses even if secondary addresses are configured on the ports.
For more information about primary and secondary IP addresses, see
Layer 3— IP Services Confi
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