Cisco ASR 9000 Series Routing Configuration Manual page 75

Implementing BGP
Multiprotocol BGP is useful when you want a link dedicated to multicast traffic, perhaps to limit which
resources are used for which traffic. Multiprotocol BGP allows you to have a unicast routing topology different
from a multicast routing topology providing more control over your network and resources.
In BGP, the only way to perform interdomain multicast routing was to use the BGP infrastructure that was
in place for unicast routing. Perhaps you want all multicast traffic exchanged at one network access point
(NAP). If those routers were not multicast capable, or there were differing policies for which you wanted
multicast traffic to flow, multicast routing could not be supported without multiprotocol BGP.
It is possible to configure BGP peers that exchange both unicast and multicast network layer reachability
Note
information (NLRI), but you cannot connect multiprotocol BGP clouds with a BGP cloud. That is, you
cannot redistribute multiprotocol BGP routes into BGP.
Figure 4: Noncongruent Unicast and Multicast Routes, on page 45
topologies that are incongruent, and therefore are not possible without multiprotocol BGP.
Autonomous systems 100, 200, and 300 are each connected to two NAPs that are FDDI rings. One is used
for unicast peering (and therefore the exchange of unicast traffic). The Multicast Friendly Interconnect (MFI)
ring is used for multicast peering (and therefore the exchange of multicast traffic). Each router is unicast and
multicast capable.
Figure 4: Noncongruent Unicast and Multicast Routes
Figure 5: Multicast BGP Environment, on page 46
routers. The two routers on the left are unicast-only routers (that is, they do not support or are not configured
to perform multicast routing). The two routers on the right are multicast-only routers. Routers A and B support
both unicast and multicast routing. The unicast-only and multicast-only routers are connected to a single NAP.
In Figure 5: Multicast BGP Environment, on page
unicast routers to Router B and back. Multicast traffic could not flow on that path, so another routing table is
required. Multicast traffic uses the path from Router A to the multicast routers to Router B and back.
Figure 5: Multicast BGP Environment, on page 46
separate unicast route and multicast route from Router A to Router B. Multiprotocol BGP allows these routes
Cisco ASR 9000 Series Aggregation Services Router Routing Configuration Guide, Release 5.3.x
illustrates simple unicast and multicast
is a topology of unicast-only routers and multicast-only
46, only unicast traffic can travel from Router A to the
illustrates a multiprotocol BGP environment with a
Multiprotocol BGP
45