H3C Technologies H3C SecPath F1000-E - Manual (Page 12)

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Based on the forwarding mechanism, PIM comes in two modes – dense mode (often referred to as
PIM-DM) and sparse mode (often referred to as PIM-SM).
• An inter-domain multicast routing protocol is used for delivery of multicast information between two
ASs. So far, mature solutions include Multicast Source Discovery Protocol (MSDP) and Multicast
Border Gateway Protocol (MBGP). MSDP is used to propagate multicast source information among
different ASs, while MBGP, an extension of the Multi-protocol Border Gateway Protocol (MP-BGP),
is used for exchanging multicast routing information among different ASs.
For the SSM model, multicast routes are not divided into intra-domain routes and inter-domain routes.
Since receivers know the positions of the multicast sources, channels established through PIM-SM are
sufficient for multicast information transport.
Layer 2 multicast protocols
Layer 2 multicast protocols include IGMP Snooping/MLD Snooping and multicast VLAN/IPv6 multicast
VLAN. Figure 9 shows where these protocols are in the network.
Figure 9 Positions of Layer 2 multicast protocols
Source
Receiver Receiver
IPv4/IPv6 multicast packets
IGMP Snooping
/MLD Snooping
Multicast VLAN
/IPv6 Multicast VLAN
1. IGMP snooping/MLD snooping
Running on Layer 2 devices, IGMP snooping and MLD snooping are multicast constraining mechanisms
that manage and control multicast groups by listening to and analyzing IGMP or MLD messages
exchanged between the hosts and Layer 3 multicast devices, thus effectively controlling the flooding of
multicast data in a Layer 2 network.
2. Multicast VLAN/IPv6 multicast VLAN
In the traditional multicast-on-demand mode, when users in different VLANs on a Layer 2 device need
multicast information, the upstream Layer 3 device must forward a separate copy of the multicast data to
each VLAN of the Layer 2 device. With the multicast VLAN or IPv6 multicast VLAN feature enabled on
the Layer 2 device, the Layer 3 multicast device sends only one copy of multicast to the multicast VLAN
or IPv6 multicast VLAN on the Layer 2 device. This avoids waste of network bandwidth and extra burden
on the Layer 3 device.
Multicast Packet Forwarding Mechanism
In a multicast model, a multicast source sends information to the host group identified by the multicast
group address in the destination address field of IP multicast packets. Therefore, to deliver multicast