Static Multicast Routes - HP A8800 Configuration Manual

If the RPF interface is not the incoming interface, this means the (S, G) entry has expired, and
router replaces the incoming interface with the RPF interface. If the interface on which the
packet arrived in the RPF interface, the router forwards the packet out of all the outgoing
interfaces; otherwise it discards the packet.
NOTE:
You can configure special processing of packets that have failed an RPF check instead of simply dropping
them. For more information, see
Assume that unicast routes are available in the network, MBGP is not enabled, and no static multicast
routes have been configured on Router C, as shown in
from the multicast source to the receivers. The multicast forwarding table on Router C contains the (S, G)
entry, with POS 5/1/1 as the RPF interface.
Figure 23 RPF check process
When a multicast packet arrives on POS 5/1/1 of Router C, as the interface is the incoming
•
interface of the (S, G) entry, the router forwards the packet out of all outgoing interfaces.
When a multicast packet arrives on POS 5/1/2 of Router C, as the interface is not the incoming
•
interface of the (S, G) entry, the router performs an RPF check on the packet: The router searches its
unicast routing table and finds that the outgoing interface to the source (the RPF interface) is POS
5/1/1. This means the (S, G) entry is correct and packet arrived along a wrong path. The RPF check
fails and the packet is discarded.

Static multicast routes

A static multicast route is an important basis for RPF checks. Depending on the application environment,
a static multicast route has the following functions:
Changing an RPF route
Typically, the topology structure of a multicast network is the same as that of a unicast network, and
multicast traffic follows the same transmission path as unicast traffic does. By configuring a static
multicast route for a given multicast source, you can change the RPF route so as to create a transmission
path for multicast traffic different from that for unicast traffic.
Figure 24 Changing an RPF route
"Configuring RPF check failure
Figure
63
processing."
23. Multicast packets travel along the SPT