Static Multicast Routes - HP 6125XLG Configuration Manual

Figure 14 RPF check process
IP Routing Table on Switch C
Destination/Mask
192.168.0.0/24
Source
192.168.0.1/24
As shown in
routes have been configured on Switch C. Multicast packets travel along the SPT from the multicast source
to the receivers. The multicast forwarding table on Switch C contains the (S, G) entry, with
VLAN-interface 20 as the incoming interface.
When VLAN-interface 20 of Switch C receives a multicast packet, because the interface is the
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incoming interface of the (S, G) entry, the switch forwards the packet out of all outgoing interfaces.
When VLAN-interface 10 of Switch C receives a multicast packet, because the interface is not the
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incoming interface of the (S, G) entry, the Switch performs an RPF check on the packet. The switch
looks up its unicast routing table and finds that the outgoing interface to the source (the RPF
interface) is VLAN-interface 20. It means that the (S, G) entry is correct, but the packet traveled
along a wrong path. The RPF check fails and the switch 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 given multicast source to change the RPF route, so that the router creates a
transmission path for multicast traffic that is different from the transmission path for unicast traffic.
Interface
Vlan-int20
Switch A
Multicast packets
Figure 14, assume that unicast routes are available in the network, and no static multicast
Switch B
Vlan-int10
Vlan-int10
Vlan-int20
Switch C
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Receiver
Receiver