Cabletron Systems SmartSwitch manual Import Policies, Import-Source

Chapter 11: Routing Policy Configuration Guide

Import Policies

Import policies control the importation of routes from routing protocols and their installation in the routing databases (Routing Information Base and Forwarding Information Base). Import Policies determine which routes received from other systems are used by the SSR routing process. Every import policy can have up to two components:

•Import-Source

•Route-Filter

Import-Source

This component specifies the source of the imported routes. It can also specify the preference to be associated with the routes imported from this source.

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

•Type of the source protocol (RIP, OSPF, BGP).

•Source interface or gateway from which the route was received.

•Source autonomous system from which the route was learned.

•AS path associated with a route. Besides autonomous system, BGP also supports importation of routes using AS path regular expressions and AS path options.

•If multiple communities are specified using the optional-attributes-list, only updates carrying all of the specified communities will be matched. If the specified optional- attributes-list has the value none for the well-known-communityoption, then only updates lacking the community attribute will be matched.

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

Note: It is quite possible for several BGP import policies to match a given update. If more than one policy matches, the first matching policy will be used. All later matching policies will be ignored. For this reason, it is generally desirable to order import policies from most to least specific. An import policy with an optional- attributes-list will match any update with any (or no) communities.

The importation of RIP routes may be controlled by source interface and source gateway. RIP does not support the use of preference to choose between RIP routes. That is left to the protocol metrics.

Due to the nature of OSPF, only the importation of ASE routes may be controlled. OSPF intra-and inter-area routes are always imported into the routing table with a preference of

10.If a tag is specified with the import policy, routes with the specified tag will only be imported.

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