Avaya Configuring IP Multicasting and Multimedia Services Bedienungsanleitung PDF herunterladen (Seite 203)

Customizing Protocol Independent Multicast

117355-D Rev 00

6-17

How the Last-Hop Router Switches to the Shortest-Path Tree

The following steps, which are illustrated in Figure 6-6, describe how the last-hop

router switches from the shared tree to the shortest-path tree when it has

downstream group members:

The last-hop router receives native multicast packets from the RP.

If the data rate of the packets sent from the RP exceeds the data threshold

configured on the last-hop router, the last-hop router immediately sends a join

message toward the DR of the source. This message establishes a

shortest-path tree between the source and the last-hop router.

All intermediate routers along the path to the last-hop router add a new

entry (*, group) in their multicast forwarding tables. This entry establishes a

delivery path that all intermediate routers can use to forward subsequent

messages from the source’s DR to the last-hop router on the shortest-path tree.

After the source’s DR receives the join message from the last-hop router, it

sends native multicast packets toward the last-hop router on the shortest-path

tree.

The last-hop router now receives multicast packets from the RP on the shared

tree and from the source’s DR on the shortest-path tree. To avoid receiving

duplicate packets, the last-hop router sends a prune message toward the RP,

indicating that it wants to receive packets on the shortest-path tree only.

For information about configuring a last-hop router to switch to the SPT, see

“Modifying the Last-Hop Threshold

” on page 6-20.

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Avaya Configuring IP Multicasting and Multimedia Services Bedienungsanleitung Seite 203