Riverstone Networks WICT1-12 - Manual (Page 434)

18-4 Riverstone Networks RS Switch Router User Guide Release 8.0
Preference Routing Policy Configuration
Export-Destination
This component specifies the destination where the routes are to 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 be redistributed
are a few examples of export-destinations. The metric, type, tag, and AS-Path are a few examples of attributes
associated with the exported routes.
Export-Source
This component specifies the source of the exported routes. It can also 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:
• Their protocol type (RIP, OSPF, BGP, Static, Direct, Aggregate, IS-IS).
• 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, BGP, and IS-IS) 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.
18.1.3 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.