Configuring Ipv6 Multicast Routing And Forwarding; Overview; Rpf Check Mechanism - HP MSR1002-4 Configuration Manual

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.

RPF check mechanism

An IPv6 multicast routing protocol uses the reverse path forwarding (RPF) check mechanism to
ensure IPv6 multicast data delivery along the correct path and to avoid data loops.
RPF check process
An IPv6 multicast router performs the RPF check on an IPv6 multicast packet as follows:
1. The router chooses an optimal route back to the packet source separately from the IPv6 unicast
and IPv6 MBGP routing tables.
In RPF check, the "packet source" means difference things in difference situations:
For a packet that travels along the SPT, the packet source is the IPv6 multicast source.

For a packet that travels along the RPT, the packet source is the RP.

For a bootstrap message originated from the BSR, the packet source is the BSR.

For more information about the concepts of SPT, RPT, source-side RPT, RP, and BSR, see
"Configuring IPv6 PIM."
2. The router selects one of the optimal routes as the RPF route as follows:
If the router uses the longest prefix match principle, the route with a higher prefix length

becomes the RPF route. If the routes have the same prefix length, the route with a higher
route preference becomes the RPF route. If the routes have the same route preference, the
IPv6 MBGP route becomes the RPF route.
For more information about the route preference, see Layer 3—IP Routing Configuration
Guide.
If the router does not use the longest prefix match principle, the route with a higher route

preference becomes the RPF route. If the routes have the same route preference, the IPv6
MBGP route becomes the RPF route.
In the RPF route, the outgoing interface is the RPF interface and the next hop is the RPF
neighbor.
3. The router checks whether the packet arrived at the RPF interface. If yes, the RPF check
succeeds and the packet is forwarded. If not, the RPF check fails and the packet is discarded.
RPF check implementation in IPv6 multicast
Implementing an RPF check on each received IPv6 multicast packet would heavily burden the
router. The use of an IPv6 multicast forwarding table is the solution to this issue. When the router
creates an IPv6 multicast forwarding entry for an IPv6 (S, G) packet, it sets the RPF interface of the
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