Cabletron Systems SmartSwitch 8-slot User's Reference Manual

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Cabletron Systems SmartSwitch 8-slot User's Reference Manual Manual pdf 87 page image

Chapter 6: Routing Policy Configuration GuideSSR User Reference Manual6 - 15Configure Advanced Routing PoliciesAdvanced Routing Policies are used for creating complex import/export policies thatcannot be done using the redistribute command. Advanced export policies providegranular control over the targets where the routes are exported, the source of theexported routes, and the individual routes which are exported. It provides thecapability to send different routes to the various route-peers. They can be used toprovide the same route with different attributes to the various route-peers.Import policies control the importation of routes from routing protocols and theirinstallation in the routing database (Routing Information Base and ForwardingInformation Base). Import policies determine which routes received from othersystems are used by the SSR routing process. Using import policies, it is possible toignore route updates from an unreliable peer and give better preference to routeslearned from a trusted peer.Export PoliciesAdvanced export policies can be constructed from one or more of the followingbuilding blocks:• Export Destinations - This component specifies the destination where the routes areto be exported. It also specifies the attributes associated with the exported routes.The interface, gateway or the autonomous system to which the routes are to beredistributed are a few examples of export-destinations. The metric, type, tag, andAS-Path are a few examples of attributes associated with the exported routes.• Export Sources - This component specifies the source of the exported routes. It canalso specify the metric to be associated with the routes exported from this source.The routes to be exported can be identified by their associated attributes, such asprotocol type, interface or the gateway from which the route was received, and so on.• Route Filter - This component provides the means to define a filter for the routes tobe distributed. Routes that match a filter are considered as eligible for redistribution.This can be done using one of two methods:• Creating a route-filter and associating an identifier with it. A route-filter has sev-eral network specifications associated with it. Every route is checked against theset of network specifications associated with all route-filters to determine its eli-gibility for redistribution. The identifier associated with a route-filter is used in theip-router policy export command.• Specifying the networks as needed in the ip-router policy export command.If you want to create a complex route-filter, and you intend to use that route-filter inseveral export policies, then the first method is recommended. It you do not have