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ADC Telecommunications, Inc.
224 C
HAPTER 11: CREATING ROUTE FILTERS
About RIP and OSPF Route Maps
The system uses route filtering functions to control the flow of routes to and
from other RIP and OSPF routers. Two filtering functions are supported for
control of RIP and OSPF routes:
■ Import — Controls how routes are added to the system’s routing table.
■ Export — Controls which routes are advertised to other routers.
Route filtering is used to customize connectivity, increase security, conserve
routing table space, or adjust route cost.
In order to understand route filtering, you must be familiar with the
following functions:
■ Route-Map — The route map defines the match criteria and the action
that you want the system to take when a match is found. You use the
route-map command to create a route-map and enter configuration
mode for the route-map. When you define a route-map, you specify a
permit or deny action. You then define the match criteria of a route map
using the match command. In addition, you can choose to define
override actions using the override command.
■ Map-List — A sequential grouping of route-maps. Routes are
sequentially compared against all route-maps that comprise the map-list.
When a match is found, the action defined by the route-map is invoked,
and further exploration of the route-map is ended. If the system does not
find a match, then no action is taken.
Defining RIP and OSPF route filtering is a two-step process:
■ First, you create route maps to define match criteria and the action that
you want the system to take when it finds a match. You can choose to
permit or deny a route, as well as override route cost, tag, or preference.
■ Second, you arrange those route-maps into map-lists.
When defining route maps and map lists, remember the following:
■ Map lists are made up of one or more route maps.
■ The same route map may be shared among multiple map lists.
■ Route maps within each map list must be sorted in order of the
specific-to-general match criteria and action needs of the map list.