Routing TCPIP, Vol. II, (CCIE Professional Development) by Jeff Doyle Jennifer DeHaven Carroll & Jennifer DeHaven Carroll

Author:Jeff Doyle,Jennifer DeHaven Carroll & Jennifer DeHaven Carroll
Language: eng
Format: epub
Publisher: Pearson Education Limited (US titles)
Published: 2003-03-15T05:00:00+00:00

Figure 5-54 A Source-Based Tree Might Be Preferable to the Shared Tree in This Internetwork

Unlike CBT, PIM-SM supports both shared and source-based trees, which is the primary reason it is presently the multicast routing protocol of choice in most modern internetworks.

PIM-SM is described in RFC 2362.13

PIM-SM Basics

PIM-SM uses seven PIMv2 messages:

• Hello

• Bootstrap

• Candidate-RP-Advertisement

• Join/Prune

• Assert

• Register

• Register-Stop

Notice that three of the messages (Hello, Join/Prune, and Assert) also are used by PIM-DM. There are four messages unique to PIM-SM, just as there are two messages (Graft and Graft-Ack) used only by PIM-DM.

Several functions are common to PIM-SM and PIM-DM:

• Neighbor discovery through exchange of Hello messages

• Recalculation of the RPF interface when the unicast routing table changes

• Election of a designated router on multiaccess networks

• The use of Prune Overrides on multiaccess networks

• Use of Assert messages to elect a designated forwarder on multiaccess networks

These functions are all described in the PIM-DM section and so are not described again here.

Unlike PIM-DM, PIM-SM uses explicit joins, making the creation of both shared and source-based multicast trees more efficient.

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