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Introduction to multicast traceroute packets
A multicast traceroute packet is a special IGMP packet that is different from common IGMP packets. The
difference lies 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—Its IGMP Type field set to 0x1F.
Request—Its IGMP Type field set to 0x1F.
•
Response—Its 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 to the end of the packet. The response data block contains its interface
addresses and packet statistics. 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. Then, it unicasts the completed packet to the querier.
Configuration task list
Task
Enabling IP multicast routing
Configuring multicast routing
and forwarding
IP multicast does not support secondary IP addresses. Namely, multicast can be routed and forwarded
only through primary IP addresses even if secondary IP addresses are configured on the ports. For more
information about primary and secondary IP addresses, see Layer 3—IP Services Configuration Guide.
Enabling IP multicast routing
Before you configure any Layer 3 multicast functionality, you must enable IP multicast routing.
Enabling IP multicast routing for the public network
Step
1.
Enter system view.
2.
Enable IP multicast routing.
Configuring static multicast routes
Configuring a multicast routing policy
Configuring a multicast forwarding range
Configuring the multicast forwarding table size
Tracing a multicast path
Command
system-view
multicast routing-enable
120
Remarks
Required.
Optional.
Optional.
Optional.
Optional.
Optional.
Remarks
N/A
Disabled by default.
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