H3C Technologies H3C S7500E Series Switches - Manual (Page 91)

4-7
Multicast Traceroute
The multicast traceroute utility is used to trace the path that a multicast stream flows down from
the first-hop router to the last-hop router.
Concepts in multicast traceroute
1) Last-hop router: If a router has one of its interfaces connecting to the subnet the given
destination address is on, and if the router is able to forward multicast streams from the
given multicast source onto that subnet, that router is called last-hop router.
2) First-hop router: the router that directly connects to the multicast source.
3) Querier: the router requesting the multicast traceroute.
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 that its destination IP address is a
unicast address. There are three types of multicast traceroute packets:
z Query, with the IGMP Type field set to 0x1F,
z Request, with the IGMP Type field set to 0x1F, and
z 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) Upon receiving the query, the last-hop router turns the query packet into a request packet
by adding a response data block containing its interface addresses and packet statistics to
the end of the packet, and forwards the request packet via 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 via unicast to the
multicast traceroute querier.
Configuration Task List
Complete these tasks to configure multicast routing and forwarding:
Task Remarks
Enabling IP Multicast Routing Optional
Configuring Multicast Static Routes Optional
Configuring a Multicast Routing Policy Optional
Configuring a Multicast Forwarding Range Optional
Configuring the Multicast Forwarding Table Size Optional
Configuring Multicast
Routing and Forwarding
Configuring Static Multicast MAC Address Entries Optional