[HomeButton] [TOCButton] [IndexBtn] [FeedbackButton]

Routing Policy (Route Filtering)

The routing policy represents a set of rules that defines the relation between the router and the external world in terms of route exchanges and protocol interaction. The choice of a routing policy allows the user to define:

Routing policy is an important part of the Ipsrd configuration; it should not be neglected, especially when running several different protocols on the same router (for example igp, egp, static routes, and direct routes). Routing policy is often referred to as route filtering, since defining a policy is equivalent to defining a set of filters to apply to a route before accepting or redistributing it.

Import Policy

The import policy defines the set of routes that is accepted criteria for accepting a route includes parameters like:

Export Policy

The export policy defines the set of routes that is exported to the external world by any protocol. The criteria are the same as for the import policy.

The export policy also defines the redistribution of routes between the various routing protocols on the router. By default, a given protocol redistributes only the routes originated from that protocol and the directly-attached networks. As examples, RIP announces only routes learned from RIP and interfaces running RIP, and BGP announces only routes learned from other BGP peers. The export policy allows the protocols to exchange routes between each other, make external routes available for redistribution by internal protocols, and vice-versa. The export policy is also very useful for advertising static routes (like a default route) through any protocol.

Route Filtering

A route filter is a list of routes, given by address (prefix) and masks, against which a given route is matched. All the routing policy statements make use of a route filter to explicitly define the set of routes accepted or announced.


[HomeButton] [TOCButton] [IndexBtn] [FeedbackButton]

Copyright © 1997 Ipsilon Networks, Inc.
Portions copyright © Digital Equipment Corporation 1998. All rights reserved.
Updated January 8, 1998
Send comments to Digital Equipment Corporation, doc-quality@lkg.mts.dec.com