Overview of PIM

Definition

Protocol Independent Multicast (PIM) is a multicast routing solution that uses unicast routing table to perform reverse path forwarding (RPF) checks on multicast packets and creates multicast routing entries if multicast packets pass RPF checks. PIM does not depend on any particular unicast routing protocol for topology discovery.

Currently, Huawei switches support PIM-DM and PIM-SM.

Purpose

The multicast backbone (Mbone) was established in 1992 as a virtual backbone for IP multicast traffic to support network video and audio conferencing. Mbone uses Multicast Open shortest Path First (MOSPF) and the Distance Vector Multicast Routing Protocol (DVMRP).

Mbone promotes the use and development of multicast technology and routing multicast protocols. However, new problems arise: If multicast routes need to be created using multiple routing protocols, different protocols need to import routes of each other, which involves complex operations. Additionally, network devices need to maintain both unicast and multicast routing information.

PIM was developed to simplify operations and reduce network device load by eliminating the need to maintain a large amount of routing information. Instead, network devices only need to main group member and source information and obtain routing information from the unicast routing table. PIM is most widely used intra-domain multicast protocol.

A PIM network is comprised of multiple PIM routers. A large PIM network can be partitioned into multiple PIM domains to manage and control multicast packet forwarding.