H3C Technologies H3C S12500-X Series Switches - Manual (Page 138)

128
Configuring IPv6 multicast routing and
forwarding
Overview
IPv6 multicast routing and forwarding uses the following tables:
• IPv6 multicast protocols' routing tables, such as the IPv6 PIM routing table.
• General IPv6 multicast routing table that summarizes the multicast routing information generated by
different IPv6 multicast routing protocols. The IPv6 multicast routing information from IPv6 multicast
sources to IPv6 multicast groups are stored in a set of (S, G) routing entries.
• IPv6 multicast forwarding table that guides IPv6 multicast forwarding. The optimal routing entries in
the IPv6 multicast routing table are added to the IPv6 multicast forwarding table.
The term "interface" in this chapter collectively refers to VLAN interfaces and Layer 3 Ethernet interfaces.
You can set an Ethernet port as a Layer 3 interface by using the port link-mode route command (see
Layer 2—LAN Switching Configuration Guide).
RPF check mechanism
An IPv6 multicast routing protocol relies on the existing IPv6 unicast routing information in creating IPv6
multicast routing entries. When creating IPv6 multicast routing table entries, an IPv6 multicast routing
protocol uses the reverse path forwarding (RPF) check mechanism to ensure IPv6 multicast data delivery
along the correct path. The RPF check mechanism also helps avoid data loops.
A multicast routing protocol uses IPv6 unicast routing table to perform the RPF check. The IPv6 unicast
routing table contains unicast routing information.
RPF check process
A router performs an RPF check based on its IPv6 unicast routing table. When performing the RPF check,
the router uses the packet's source IPv6 address as the destination address to look up the IPv6 unicast
routing table. It automatically selects an optimal route, of which the outgoing interface is the RPF interface
and the next hop is the RPF neighbor. If the RPF interface receives the IPv6 multicast packet from the RPF
neighbor, the router considers the path of the IPv6 multicast packet the shortest path that leads back to
the source.
The term "packet source" means different things in different situations:
• For a packet that travels along the SPT from the multicast source to the receivers or the RP, the packet
source for RPF check is the multicast source.
• For a packet that travels along the RPT from the RP to the receivers, or along the source-side RPT from
the multicast source to the RP, the packet source for RPF check is the RP.
• For a bootstrap message from the BSR, the packet source for RPF check is the BSR.
For more information about the concepts of SPT, RPT, source-side RPT, RP, and BSR, see " Configuring IPv6
PIM ."