H3C Technologies H3C S10500 Series Switches - Manual (Page 91)

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Multicast routing and forwarding configuration
NOTE:
•
The term router in this document refers to both routers and Layer 3 switches.
• The term interface in the multicast routing and forwarding features refers to Layer 3 interfaces, including
VLAN interfaces and route-mode (or Layer 3) Ethernet ports. You can set an Ethernet port to operate in
route mode by using the port link-mode route command (see Layer 2—LAN Switching Configuration
Guide).
Multicast routing and forwarding overview
In multicast implementations, the following types of tables implement multicast routing and forwarding:
• Multicast routing table of a multicast routing protocol—Each multicast routing protocol has its own
multicast routing table, such as PIM routing table.
• General multicast routing table—The multicast routing information of different multicast routing
protocols forms a general multicast routing table.
• Multicast forwarding table—The multicast forwarding table guides the forwarding of multicast
packets.
A multicast routing table consists of a set of (S, G) entries. Each entry indicates the routing information for
delivering multicast data from a multicast source to a multicast group. If a router supports multiple
multicast protocols, its multicast routing table includes routes generated by multiple protocols. The router
chooses the optimal route from the multicast routing table based on the configured multicast routing and
forwarding policy and adds the route entry to its multicast forwarding table.
RPF check mechanism
A multicast routing protocol relies on the existing unicast routes, MBGP routes, or multicast static routes
in creating multicast routing entries. When creating multicast routing table entries, a multicast routing
protocol uses the reverse path forwarding (RPF) check mechanism to ensure multicast data delivery along
the correct paths. In addition, the RPF check mechanism also helps avoid data loops.
RPF check process
The basis for an RPF check is as follows:
• Unicast routing table—Contains the shortest path to each destination subnet.
• MBGP routing table—Contains multicast routing information.
• Multicast static routing table—Contains the RPF routing information defined by the user through
static configuration.
When a router performs an RPF check, it searches its unicast routing table, MBGP routing table, and
multicast static routing table at the same time. The specific process is as follows:
1. The router chooses an optimal route from the unicast routing table, the MBGP routing table, and
the multicast static routing table: