3com 5500-ei pwr Installation Instruction

 

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Generally, we refer to IP multicast working at the network layer as Layer 3 multicast and the 

corresponding multicast protocols as Layer 3 multicast protocols, which include IGMP, PIM, and 

MSDP; we refer to IP multicast working at the data link layer as Layer 2 multicast and the 

corresponding multicast protocols as Layer 2 multicast protocols, which include IGMP Snooping.  

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This section provides only general descriptions about applications and functions of the Layer 2 and 

Layer 3 multicast protocols in a network. For details about these protocols, refer to the related 

chapters of this manual.  

 

Layer 3 multicast protocols include multicast group management protocols and multicast routing 

protocols. 

 describes where these multicast protocols are in a network. 

Figure 1-5 Positions of Layer 3 multicast protocols 

Source

Receiver

Receiver

Receiver

 

 

1)  Multicast management protocols  

Typically, the Internet Group Management Protocol (IGMP) is used between hosts and Layer 3 

multicast devices directly connected with the hosts. These protocols define the mechanism of 

establishing and maintaining group memberships between hosts and Layer 3 multicast devices.  

2)  Multicast routing protocols 

A multicast routing protocol runs on Layer 3 multicast devices to establish and maintain multicast routes 

and forward multicast packets correctly and efficiently. Multicast routes constitute a loop-free data 

transmission path from a data source to multiple receivers, namely a multicast distribution tree. 

In the ASM model, multicast routes come in intra-domain routes and inter-domain routes. 

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An intra-domain multicast routing protocol is used to discover multicast sources and build multicast 

distribution trees within an autonomous system (AS) so as to deliver multicast data to receivers.