Forwarding Mechanism Of Multicast Packets - H3C S7500 Series Operation Manual

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Operation Manual – Multicast

H3C S7500 Series Ethernet Switches

Figure 1-5 Positions of multicast-relevant protocol

I. Multicast group management protocol

Internet group management protocol (IGMP) runs between hosts and multicast routers.

This protocol defines the mechanism of establishing and maintaining group

membership between hosts and routers.

II. Multicast routing protocols

A multicast routing protocol operates between multicast routers to establish and

maintain multicast routes and forward multicast packets accurately and effectively. A

multicast route establishes a loop-free data transmission path from a data source to

multiple receivers. The multicast routing protocol is designed to establish a distribution

tree. Multicast routers can establish the data transmission path (namely, distribution

tree) in many ways.

Like unicast routes, multicast routes come in intra-domain routes and inter-domain

routes. Intra-domain multicast routes are quite mature now. Protocol independent

multicast (PIM) is the most commonly used protocol currently. It can cooperate with any

unicast routing protocol.

1.3 Forwarding Mechanism of Multicast Packets

In a multicast model, a multicast source transmits information to the multicast group,

which is identified by the multicast group address in the destination address field of an

IP data packet. Unlike a unicast model, a multicast model must forward data packets to

multiple external interfaces so that all receivers can receive the packets. Therefore the

forwarding process of multicast is more complicated than unicast.

Chapter 1 Multicast Overview

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