Information Technology Reference
In-Depth Information
To summarize, the recommended practices regarding summarization include the follow ing:
Implement summarization at WAN connectivity and remote-access points toward the
network core, to reduce the routing table size.
Summarize at the distribution layer for all network at interfaces that point to the net-
work core.
Implement passive interfaces on access layer interfaces so that neighbor adjacencies
are not established through the access layer. A more-specific route might be created,
which would be taken over a summarized route.
Route Redistribution
Route redistribution is an exchange of routes between routing protocols (for example, be-
tween EIGRP and OSPF). You configure the redistribution of routing protocols on routers
that reside at the service provider edge of the network. These routers exchange routes
with other autonomous systems. Redistribution is also done on routers that run more than
one routing protocol. Here are some reasons to do redistribution:
Key
To p i c
Migration from an older routing protocol to a new routing protocol.
Mixed-vendor environment in which Cisco routers might be using EIGRP and other
vendor routers might be using OSPF.
Different administrative domain between company departments using different rout-
ing protocols.
Mergers and acquisitions in which the networks initially need to communicate. In this
scenario, two different EIGRP processes might exist.
Figure 11-19 shows an example of the exchange of routes between two autonomous
systems. Routes from autonomous system 100 are redistributed into BGP on Router A.
Routes from autonomous system 200 are redistributed into BGP on Router B. Then,
Routers A and B exchange BGP routes. Router A and Router B also implement filters to
redistribute only the desired networks.
OSPF 100
Router A
BGP
Redistribution of Routes
Router B
OSPF 200
Figure 11-19
Redistribution of BGP Routes
 
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