Multicast Static Route - 3Com MSR 50 Series Configuration Manual

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HAPTER ULTICAST

Multicast static route

R F C
OUTING AND ORWARDING
means that the interface on which the packet actually arrived is not the RPF
interface. The RPF check fails and the packet is discarded.
A multicast packet from Source arrives on POS5/1 of Router C, and the
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corresponding forwarding entry does not exist in the multicast forwarding
table of Router C. The router performs an RPF check, and finds in its unicast
routing table that the outgoing interface to 192.168.0.0/24 is the interface on
which the packet actually arrived. The RPF check succeeds and the packet is
forwarded.
If the topology structure of a multicast network is the same as that of a unicast
network, receivers can receive multicast data via unicast routes. However, the
topology structure of a multicast network may differ from that of a unicast
network, and some routers may support only unicast but not multicast. In this
case, you can configure multicast static routes to provide multicast transmission
paths that are different from those for unicast traffic. Note the following two
points:
A multicast static route only affects RPF checks, instead of guiding multicast
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forwarding, so it is also called an RPF static route.
A multicast static route is effective on the multicast router on which it is
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configured, and will not be broadcast throughout the network or injected to
other routers.
A multicast static route is an important basis for RPF checks. With a multicast static
route configured on a router, the router searches the unicast routing table and the
multicast static routing table simultaneously in a RPF check, chooses the optimal
unicast RPF route and the optimal multicast static route respectively from the
routing tables, and uses one of them as the RPF route after comparison.
Figure 326 Multicast static route
Multicast Routing Table Static on Router C
Destination/Mask Interface
192.168.0.0/24 POS5/0
Multicast packets
Multicast static route
Source
192 .168 .0 .1/24
As shown in Figure 326, when no multicast static route is configured, Router C's
RPF neighbor on the path back to Source is Router A and the multicast
information from Source travels along the path from Router A to Router C, which
is the unicast route between the two routers; with a static route configured on
Router C and Router B as Router C's RPF neighbor on the path back to Source, the
ONFIGURATION
RPF neighbor/Mask
1.1.1.1/24
Router A
Router B
POS 5/1
POS 5/0
1 .1.1.1/24
POS 5/0
1 .1.1.2/24
POS5 /1
Router C
Receiver
Receiver