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Configuration Guide - IP Multicast

S7700 and S9700 V200R010C00

This document describes IP multicast basics and how to configure IP multicast features, including IGMP/MLD, PIM (IPv4&IPv6), MSDP, multicast VPN, Layer 3 multicast CAC, Layer 2 multicast CAC, IGMP/MLD snooping, and multicast VLAN, IPv4&IPv6 multicast route management, static multicast MAC address, multicast network.
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Concepts

Concepts

Concepts in this section are described with reference to the network shown in Figure 4-1.

Figure 4-1  PIM network

Multicast Distribution Tree

On a PIM network, a point-to-multipoint (P2MP) multicast forwarding path is established for each multicast group. The multicast forwarding path is also called a multicast distribution tree (MDT) because of its tree shape.

Two types of MDT are available:

  • Shortest path tree (SPT) uses the multicast source as the root and multicast group members as leaves. SPT applies to both PIM-DM and PIM-SM networks.

    In Figure 4-1, the MDT, RouterE → RouterD → RouterA/RouterB, is an SPT, on which the source is the root and HostA and HostB are leaves.

  • Rendezvous point tree (RPT) uses a rendezvous point (RP) as the root and multicast group members as leaves. RPT applies to PIM-SM networks.

    For details about RP and RPT, see PIM-SM (ASM Model).

PIM Router

Routers with PIM enabled on interfaces are called PIM routers. Roles of routers on an MDT include:

  • Leaf router

    A router that connects to user hosts, which may not be multicast group members. RouterA, RouterB, and RouterC in Figure 4-1 are leaf routers.

  • First-hop router

    A router that directly connects to the multicast source on the multicast forwarding path and is responsible for forwarding multicast data from the multicast source. RouterE in Figure 4-1 is the first-hop router.

  • Last-hop router

    A router that directly connects to multicast group members (receivers) on the multicast forwarding path and is responsible for forwarding multicast data to these members. RouterA and RouterB in Figure 4-1 are last-hop routers.

  • Intermediate router

    A router located between the first-hop and last-hop routers. RouterD in Figure 4-1 is an intermediate router.

PIM Routing Entry

A PIM routing table contains two types of PIM routing entries: (S, G) and (*, G), where S indicates a specific multicast source, G indicates a specific multicast group, and * indicates any multicast source.

  • (S, G) entries are typically used to establish an SPT on a PIM-DM or PIM-SM network.
  • (*, G) entries are typically used to establish an RPT on a PIM-SM network.

A PIM router may have both (S, G) and (*, G) entries. When a PIM router receives a multicast packet with source address S and group address G and the packet passes the RPF check, the router forwards the packet according to the following rules:

  • If a matching (S, G) entry exists, the router forwards the packet according to the (S, G) entry.
  • If no matching (S, G) entry exists but a matching (*, G) entry exists, the router creates an (S, G) entry based on the (*, G) entry, and forwards the packet according to the (S, G) entry.

PIM routing entries contain the following information to guide multicast packet forwarding:

  • Multicast source address
  • Multicast group address
  • Upstream interface, which receives multicast data on the local router, such as Int3 in Figure 4-1
  • Downstream interface, which forwards multicast data, such as Int1 and Int2 in Figure 4-1
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Updated: 2019-08-21

Document ID: EDOC1000141903

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