3Com Switch 8800 Advanced Software V5 Configuration Guide

Multicast Architecture 499

Multicast Protocols

■ 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/MLD, PIM/IPv6 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/MLD Snooping, and multicast VLAN.

■ IGMP Snooping, IGMP, PIM and MSDP are for IPv4, MLD Snooping, MLD, and

IPv6 PIM are for IPv6. Multicast VLAN are for both IPv4 and IPv6.

This section provides only general descriptions about applications and functions of

the Layer 2 and Layer 3 multicast protocols in a network. For details of these

protocols, refer to the related configuration manuals in the IP Multicast Volume.

Layer 3 multicast protocols

Layer 3 multicast protocols include multicast group management protocols and

multicast routing protocols.

Figure 160 describes where these multicast protocols

are in a network.

Figure 160 Positions of Layer 3 multicast protocols

1 Multicast management protocols

Typically, the internet group management protocol (IGMP) or multicast listener

discovery protocol (MLD) is used between hosts and Layer 3 multicast devices

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

5 Site-local scope

6, 7, 9 through D Unassigned

8 Organization-local scope

E Global scope

Table 27 Values of the Scope field

Value Meaning

AS 1 AS 2

Source

Receiver

PIM/IPv6 PIM

MSDP

IGMP/MLD