Huawei Quidway S6500 Series Operation Manual page 291

Operation Manual - Multicast Protocol
Quidway S6500 Series Ethernet Switches
I. Multicast group management protocol
Multicast groups use Internet group management protocol (IGMP) as the management
protocols. IGMP runs between the switch 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 IP Multicast Packet Forwarding
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 (such as the
MBGP multicast routing table). This check mechanism is the basis for most multicast
routing protocols to perform multicast forwarding, and is known as RPF (Reverse Path
Forwarding) check. A multicast router uses the source address of a received multicast
packet to query the unicast routing table or the independent multicast routing table to
determine that the receiving interface is on the shortest path from the receiving station
to the source. If a source tree is used, the source address is the address of the source
host sending the multicast packet. If a shared tree is used, the source address is the RP
address of the shared tree. A multicast packet arriving at the router will be forwarded
according to the multicast forwarding entry if it passes the RPF check, or else, it will be
discarded.
Huawei Technologies Proprietary
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Chapter 1 Multicast Overview