Netgear FSM726v3 7000 Series Managed Switch Administration Guide for Software - Page 442

Chapter 28 PIM In this chapter, the following examples are provided: • "PIM-DM Configuration" • "PIM-SM Configuration" on page 28-27 Note: The PIM protocol can be configured to operate on IPv4 and IPv6 networks. Separate configuration CLI commands are provided for IPv4 and IPv6 operation; however, most configuration options are common to both protocols. Therefore, this section describes only IPv4 configuration, and IPv6 configuration is similar to IPv4. Multicast protocols are used to deliver multicast packets from one source to multi-receivers. They facilitate better bandwidth utilization, and use less host and router processing, making them ideal for usage in application such as video/audio conferencing, whiteboard tools, stock distribution tickers, and so on. PIM is a widely used multicast routing protocol. Protocol Independent Multicast (PIM) is a standard multicast routing protocol that provides scalable inter-domain multicast routing across the Internet, independent of the mechanisms provided by any particular unicast routing protocol. PIM has two types: • PIM-Dense Mode (PIM-DM) • PIM-Sparse Mode (PIM-SM) PIM-DM Configuration PIM-DM protocol is a simple, protocol-independent multicast routing protocol. It uses existing Unicast routing table and join/ prune/graft mechanism to build a tree. PIM-DM creates source-based shortest-path distribution trees making use of Reverse Path Forwarding (RPF). PIM-DM cannot be used to build a shared distribution tree, as PIM-SM can. PIM-DM assumes that when a sender starts sending data, all downstream routers and hosts want to receive a multicast datagram. PIM-DM initially floods multicast traffic throughout the network. Routers that do not have any downstream neighbors prune back the unwanted traffic. Apart from the prune messages, PIM-DM makes use of two more messages: graft and assert. Graft messages are used whenever a new host wants to join the group. Assert messages are used to shut off duplicate flows onto the same multi-access network. To minimize the repeated flooding of datagrams and subsequent pruning associated with a particular (S,G) pair, PIM-DM uses a State Refresh message. This message is sent by the router(s) directly connected to the source and is propagated throughout the network. When received by a router on its RPF interface, the State Refresh message causes an existing prune state to be refreshed. State Refresh messages are generated periodically by the router directly attached to the source. There are two v1.0, October 2009 28-1