When more subnets are added, the routing table continues to grow. With summarization, the
routing table grows by only one network.
protocols. Translation between two environments using different routing protocols requires that
routes generated by one protocol be redistributed into the second routing protocol environment.
Route redistribution gives an organization the ability to run different routing protocols in
workgroups or areas where each is particularly effective. Route redistribution is also used when
Company A buys Company B and Companies A and B are running different routing protocols.
Also, redistribution is effective when migrating to a new routing protocol. By allowing its users
to employ more than one protocol, route redistribution minimizes cost while maximizing
technical flexibility.
Static route and directly connected information can also be redistributed. A default metric can
be assigned so that all redistributed routes can use the same metric.
methods by which routing information moves between routing domains. To ease configuration
of route redistribution, Cisco created route maps. A route map is a set of instructions that tells
the router how routing information is to be redistributed. Route maps contain an ordered list of
match conditions. Each item in the list is matched in turn against any route that is a candidate
for redistribution. When a match is found, an item performs an action associated with that
match. The route can be permitted (redistributed) or not permitted (not redistributed), but the
action also can mandate the use of certain administrative information (called route tags) that
can be attached to routing data to augment routing decisions.
modify the route's destination in outgoing advertisements. Where different networks share
similar redistribution needs, network administrators can conserve memory and save time by
using the same route map for more than one protocol pair. Route maps give network managers
control over the ways that routing information is propagated in their networks. Redistribution
configuration files that use route maps are easy to create, understand, and modify. Using route
maps, a CCDP can connect dissimilar networks with a great degree of control. Figure 6-11
shows route redistribution between protocols.