14.1.1 Overview of route filtering

Route filtering allows you to control which routes the switch accepts by passing routing information through a filter.

There are three types of route filtering: learned route filtering, advertised route filtering, and extranet route filtering.

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(1) Learned routes and advertised route filtering

The following figure shows the concepts of learned route filtering and advertised route filtering.

Figure 14-1: Overview of route filtering

(a) Learned route filtering

Learned route filtering works between the protocol and routing table to filter the routes the protocol learns. This allows you to control which learned routes the protocol should deem valid, or change the attributes of routes that meet certain conditions.

If you do not configure learned route filtering, all learned routes are considered valid.

(b) Advertised route filtering

Advertised route filtering works between the routing table and protocol to filter the routes in the routing table. This allows you to control which routes a protocol advertises, or change the attributes of advertised routes that meet certain conditions.

If you do not configure advertised route filtering, routes are advertised according to the policy of the associated protocol.

(2) Extranet route filtering [SL-L3A]

Implementation of an extranet requires technology that allows different VRFs to access each other. For the Switch, one method for implementing an extranet is to exchange routing information between VRF routing tables. When routing information is exchanged between VRF routing tables, extranet route filtering is used to filter routes to be exchanged. By using this filter, you can control the exchange of routing information and change the attributes of routing information to be exchanged.

If extranet route filtering has not been set up, routing information is not exchanged between VRFs.

The following figure shows the concept of extranet route filtering.

Figure 14-2: Conceptual diagram of extranet route filtering

Route filtering performed between VRFs in extranets is called inter-VRF route filtering.