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Enterasys Xpedition User Reference Manual 185

Route Import and Export Policy Overview

The routes to be exported can be identified by their associated attributes:

• Their protocol type (RIP, OSPF, BGP, Static, Direct, Aggregate).

• Interface or the gateway from which the route was received.

• Autonomous system from which the route was learned.

• AS path associated with a route. When BGP is configured, all routes are assigned an AS

path when they are added to the routing table. For interior routes, this AS path

specifies IGP as the origin and no ASs in the AS path (the current AS is added when

the route is exported). For BGP routes, the AS path is stored as learned from BGP.

• Tag associated with a route. Both OSPF and RIP version 2 currently support tags. All

other protocols have a tag of zero.

In some cases, a combination of the associated attributes can be specified to identify the

routes to be exported.

Route-Filter

This component specifies the individual routes which are to exported or restricted. The

metric to be associated with these routes can also be explicitly specified using this

component.

The metric associated with the exported routes are inherited unless explicitly specified. If

there is no metric specified with a route-filter, then the metric is inherited from the one

specified with the export-source.

If a metric was not explicitly specified with both the route-filter and the export-source,

then it is inherited from the one specified with the export-destination.

Every protocol (RIP, OSPF, and BGP) has a configurable parameter that specifies the

default-metric associated with routes exported to that protocol. If a metric is not explicitly

specified with the route-filter, export-source as well as export-destination, then it is

inherited from the default-metric associated with the protocol to which the routes are

being exported.

Specifying a Route Filter

Routes are filtered by specifying a route-filter that will match a certain set of routes by

destination, or by destination and mask. Among other places, route filters are used with

martians and in import and export policies.

The action taken when no match is found is dependent on the context. For instance, a

route that does match any of the route-filters associated with the specified import or

export policies is rejected.

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Cabletron Systems SSIM-R8-02 Spécifications Page 205