H3C S9500 Series Operation Manual page 366

Operation Manual – Multicast Protocol
H3C S9500 Series Routing Switches
Multicast
Server
Figure 1-5 Application positions of multicast-related protocols
I. Multicast group management protocol
Multicast groups use Internet group management protocol (IGMP) as the management
protocols. IGMP runs between the host and multicast router and defines the
membership establishment and maintenance mechanism between them.
II. Multicast routing protocols
A multicast routing protocol runs between multicast routers to create and maintain
multicast routes for correct and efficient forwarding of multicast packet. The multicast
routing creates a loop-free data transmission path from one source to multiple receivers.
The task of multicast routing protocols is to build up the distribution tree architecture. A
multicast router can use multiple methods to build up a path for data transmission, that
is, a distribution tree.
As in unicast routing, the multicast routing can also be intra-domain or inter-domain.
Intra-domain multicast routing is rather mature and protocol independent multicast
(PIM) is the most wildly used intra-domain protocol, which can work in collaboration
with unicast routing protocols. The inter-domain routing first needs to solve how to
transfer routing information between ASs. Since the ASs may belong to different
telecom carriers, the inter-domain routing information must contain carriers' policies, in
addition to distance information. Currently, inter-domain routing protocols include
multicast source discovery protocol (MSDP) and MBGP multicast extension.
1.3 RPF Mechanism for IP Multicast Packets
To ensure that multicast packets reach a router along the shortest path, the multicast
router must check the receiving interface of multicast packets depending on the unicast
routing table or a unicast routing table independently provided for multicast. This check
mechanism is the basis for most multicast routing protocols to perform multicast
forwarding, and is known as Reverse Path Forwarding (RPF) check. A multicast router
AS1
PIM
MBGP/MSDP
PIM
AS2
1-7
Chapter 1 IP Multicast Overview
User A
IGMP
User B
User C
IGMP
User D
IGMP
User E