Cisco Systems 78-11741-02 manual IPC-472, Unidirectional Shared Tree and Source Tree

Configuring Bidirectional PIM

Bidir-PIM Overview

Membership to a bidirectional group is signalled via explicit join messages. Traffic from sources is unconditionally sent up the shared tree toward the RP and passed down the tree toward the receivers on each branch of the tree.

Bidir-PIM is designed to be used for many-to-many applications within individual PIM domains. Multicast groups in bidirectional mode can scale to an arbitrary number of sources without incurring overhead due to the number of sources.

Bidir-PIM is derived from the mechanisms of PIM-SM and shares many shortest-path tree (SPT) operations. Bidir-PIM also has unconditional forwarding of source traffic toward the RP upstream on the shared tree, but no registering process for sources as in PIM-SM. These modifications are necessary and sufficient to allow forwarding of traffic in all routers solely based on the (*, G) multicast routing entries. This feature eliminates any source-specific state and allows scaling capability to an arbitrary number of sources. Figure 76 and Figure 77 show the difference in state created per router for a unidirectional shared tree and source tree versus a bidirectional shared tree.

Figure 76 Unidirectional Shared Tree and Source Tree

PIM source register message

Multicast
data flow	RP

(*, G)

(*, G) (*, G)

Receiver

	(*, G)
(*, G)	(*, G)
	(S, G)

Receiver Source Receiver

(A)Shared tree from RP

RP

(*, G)

(S, G)

	(*, G)
(*, G)	(S, G)

Receiver

(*, G) (S, G)

Source
(B) Source tree	33355

Cisco IOS IP Configuration Guide

IPC-472