Dell BigIron RX Series, Руководство по настройке

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BigIron RX Series Configuration Guide 801
53-1002253-01
Filtering
26
Defining route maps
A route map is a named set of match conditions and parameter settings that the router can use to
modify route attributes and to control redistribution of the routes into other protocols. A route map
consists of a sequence of instances. If you think of a route map as a table, an instance is a row in
that table. The router evaluates a route according to a route map’s instances in ascending
numerical order. The route is first compared against instance 1, then against instance 2, and so
on. As soon as a match is found, the router stops evaluating the route against the route map
instances.
Route maps can contain match statements and set statements. Each route map contains a
“permit” or “deny” action for routes that match the match statements.
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If the route map contains a permit action, a route that matches a match statement is
permitted; otherwise, the route is denied.
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If the route map contains a deny action, a route that matches a match statement is denied.
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If a route does not match any match statements in the route map, the route is denied. This is
the default action. To change the default action, configure the last match statement in the last
instance of the route map to “permit any any.”.
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If there is no match statement, the software considers the route to be a match.
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For route maps that contain address filters, AS-path filters, or community filters, if the action
specified by a filter conflicts with the action specified by the route map, the route map’s action
takes precedence over the individual filter’s action.
If the route map contains set statements, routes that are permitted by the route map’s match
statements are modified according to the set statements.
Match statements compare the route against one or more of the following:
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The route’s BGP4 MED (metric)
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A sequence of AS-path filters
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A sequence of community filters
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A sequence of address filters
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The IP address of the next hop router
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The route’s tag
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For OSPF routes only, the route’s type (internal, external type-1, or external type-2)
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An AS-path ACL
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A community ACL
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An IP prefix list
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An IP ACL
For routes that match all of the match statements, the route map’s set statements can perform
one or more of the following modifications to the route’s attributes:
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Prepend AS numbers to the front of the route’s AS-path. By adding AS numbers to the AS-path,
you can cause the route to be less preferred when compared to other routes on the basis of the
length of the AS-path.
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Add a user-defined tag to the route or add an automatically calculated tag to the route.
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Set the community value.
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Set the local preference.