67
the outgoing interface to the source (the RPF interface) is VLAN-interface 20. In this case, the
(S, G) entry is correct, but the packet traveled along a wrong path. The packet fails the RPF
check and Device C discards the packet.
Static multicast routes
Depending on the application environment, a static multicast route can change an RPF route or
create an RPF route.
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. You can configure a static
multicast route for a multicast source to change the RPF route. As a result, the router creates a
transmission path for multicast traffic that is different from the transmission path for unicast traffic.
Figure 26 Changing an RPF route
As shown in
, when no static multicast route is configured, Device C's RPF neighbor on the
path back to the source is Device A. The multicast data from the source travels through Device A to
Device C. You can configure a static multicast route on Device C and specify Device B as Device C's
RPF neighbor on the path back to the source. The multicast data from the source travels along the
path: Device A to Device B and then to Device C.
Creating an RPF route
When a unicast route is blocked, multicast forwarding might be stopped due to lack of an RPF route.
You can configure a static multicast route to create an RPF route. In this way, a multicast routing
entry is created to guide multicast forwarding.
Receiver
Device A
Device B
Device C
Vlan-int20
Vlan-int10
1.1.1.1/24
Multicast packets
Source
192.168.0.1/24
Receiver
Vlan-int10
1.1.1.2/24
Static multicast route
Source/Mask
Static multicast routing table on Device C
192.168.0.0/24
Interface
Vlan-int10
RPF neighbor/Mask
1.1.1.1/24
