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Configuration Guide - IP Multicast

CloudEngine 8800, 7800, 6800, and 5800 V200R005C10

This document describes the configurations of IP multicast, including IP multicast basics, IGMP, MLD, PIM (IPv4), PIM (IPv6), MSDP, multicast VPN, multicast route management (IPv4), multicast route management (IPv6), IGMP snooping, MLD snooping, static multicast MAC address, multicast VLAN, multicast network management.
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PIM-SM (SSM Model)

PIM-SM (SSM Model)

Implementation

Source-Specific Multicast (SSM) model uses IGMPv3/MLDv2 and PIM-SM technology. There is no need to maintain an RP, set up an RPT, or register a multicast source. An SPT can be built directly between the source and group members.

In the SSM model, user hosts know the positions of multicast sources in advance of requesting multicast services. When user hosts join multicast groups, they can specify the sources from which they want to receive data. After receiving requests from user hosts, the receiver DR sends a Join message to the source DR. The Join message is then transmitted upstream hop by hop to set up an SPT between the source and group members.

In the SSM model, PIM-SM uses the following mechanisms: neighbor discovery, DR election, and SPT setup. For details about all of these three mechanisms, see the sections below.

Neighbor Discovery

Neighbor discovery in PIM-SM (SSM model) is similar to that in PIM-SM (ASM model). For details, see "PIM-SM (ASM model) Neighbor Discovery".

DR Election

DR election in PIM-SM (SSM model) is similar to that in PIM-SM (ASM model). For details, see "PIM-SM (ASM model) DR Election".

SPT Setup

Figure 4-15 SPT setup

Figure 4-15 shows the SPT setup process:

  1. Using IGMPv3/MLDv2, RouterD and RouterE learn that packets from user hosts have the same multicast group address but are requesting multicast data from different source addresses. They send Join messages to sources hop by hop.
  2. PIM routers create (S1, G) and (S2, G) entries based on the Join messages and set up SPTs from S1 to HostA and from S2 to HostB.
  3. After SPTs are set up, the sources forward multicast packets along the SPTs to group members.

Comparison with the ASM Model

The major difference between the SSM and ASM models is that the SSM model allows hosts to specify desired multicast sources and the ASM does not. Table 4-1 describes differences of the two models.

Table 4-1 Comparisons between PIM implementations
Protocol Model Usage Scenario Implementation
PIM-SM

(Protocol Independent Multicast-Sparse Mode)

ASM model Large-scale network where multicast group members are distributed sparsely An MDT is set up when receivers join a multicast group. PIM-SM needs to maintain an RP, set up an RPT, and register a multicast source.
SSM model Scenarios where user hosts know the exact positions of multicast sources in advance and can specify the sources from which they want to receive data before they join multicast groups PIM-SSM does not need to maintain an RP, set up an RPT, or register a multicast source.
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Updated: 2019-04-20

Document ID: EDOC1100075361

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