Riverstone Networks WICT1-12 - Manual (Page 444)

18-14 Riverstone Networks RS Switch Router User Guide Release 8.0
Configuring Advanced Routing Policies Routing Policy Configuration
Import policies control the importation of routes from routing protocols and their installation in the routing database
(Routing Information Base and Forwarding Information Base). Import policies determine which routes received from
other systems are used by the RS routing process. Using import policies, it is possible to ignore route updates from an
unreliable peer and give better preference to routes learned from a trusted peer.
18.3.1 Export Policies
Advanced export policies can be constructed from one or more of the following building blocks:
• Export Destinations - 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 Sources - 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, such as protocol 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 to be 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 several network
specifications associated with it. Every route is checked against the set of network specifications
associated with all route-filters to determine its eligibility for redistribution. The identifier
associated with a route-filter is used in the
ip-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 in several export policies, then
the first method is recommended. It you do not have complex filter requirements, then use the second method.
After you create one or more building blocks, they are tied together by the
iprouter policy export
command.
To create route export policies, enter the following command in Configure mode:
<exp-dest-id> The identifier of the export-destination which determines where the routes are to be exported. If no
routes to a particular destination are to be exported, then no additional parameters are required.
<exp-src-id> If specified, is the identifier of the export-source which determines the source of the exported routes.
If a export-policy for a given export-destination has more than one export-source, then the
ip-router policy export destination
<exp-dest-id> command should be repeated for each
<exp-src-id>.
Create an export policy.
ip-router policy export destination
<exp-dest-id>
[source
<exp-src-id>
[filter
<filter-id>
|[network
<ipAddr-mask>
[exact|refines|between
<low-high>
] [metric
<number>
|restrict]]]]