H3C Technologies H3C S12500 Series Switches - Manual (Page 347)

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Configuring IPv6 multicast routing and
forwarding
Overview
In IPv6 multicast implementations, multicast routing and forwarding are implemented by routing and
forwarding tables:
• Each IPv6 multicast routing protocol has its own multicast routing table, such as the IPv6 PIM routing
table.
• The multicast routing information of different IPv6 multicast routing protocols forms a general IPv6
multicast routing table.
• The IPv6 multicast forwarding table helps guide the forwarding of IPv6 multicast packets. This is the
table that guides IPv6 multicast forwarding.
An IPv6 multicast forwarding 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 IPv6 multicast protocols, its IPv6 multicast routing table will include routes that these protocols
have generated. The router chooses the optimal route from the IPv6 multicast routing table based on the
configured multicast routing and forwarding policy and installs the route entry into its IPv6 multicast
forwarding table.
The term "router" in this document refers to both routers and Layer 3 switches.
RPF check mechanism
An IPv6 multicast routing protocol relies on the existing IPv6 unicast routing information or IPv6 MBGP
routes 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
caused by various reasons.
The basis for an RPF check is an IPv6 unicast route or an IPv6 MBGP route.
• An IPv6 unicast routing table contains the shortest path to each destination subnet.
• An IPv6 MBGP routing table contains IPv6 multicast routing information.
When performing an RPF check, a router searches its IPv6 unicast routing table and IPv6 MBGP routing
table at the same time. The process is as follows:
1. The router chooses an optimal route from the IPv6 unicast routing table and IPv6 MBGP routing
table.
{
The router searches its IPv6 unicast routing table by using the IPv6 address of the packet source
as the destination address and automatically selects the optimal route as the RPF route. The
outgoing interface in the corresponding routing entry is the RPF interface and the next hop is the
RPF neighbor. The router considers the path along which the IPv6 multicast packet from the RPF
neighbor arrived on the RPF interface to be the shortest path that leads back to the source.