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Configuring IP Routing Protocol-Independent Features
Enabling Policy Routing (PBR)
IPC-373
Cisco IOS IP Configuration Guide
For example, consider a router using IGRP and RIP. Suppose you trust the IGRP-derived routing
information more than the RIP-derived routing information. In this example, because the default IGRP
administrative distance is lower than the default RIP administrative distance, the router uses the
IGRP-derived information and ignores the RIP-derived information. However, if you lose the source of
the IGRP-derived information (because of a power shutdown in another building, for example), the
router uses the RIP-derived information until the IGRP-derived information reappears.
For an example of filtering on sources of routing information, see the section “Administrative Distance
Examples” later in this chapter.
Note You also can use administrative distance to rate the routing information from routers running the same
routing protocol. This application is generally discouraged if you are unfamiliar with this particular use
of administrative distance, because it can result in inconsistent routing information, including
forwarding loops.
Note The weight of a route can no longer be set with the distance command. To set the weight
for a route, use a route-map.
Enabling Policy Routing (PBR)
Policy routing (or “policy-based routing” [PBR]) is a more flexible mechanism for routing packets than
destination routing. It is a process whereby the router puts packets through a route map before routing
them. The route map determines which packets are routed to which router next. You might enable policy
routing if you want certain packets to be routed some way other than the obvious shortest path. Possible
applications for policy routing are to provide equal access, protocol-sensitive routing, source-sensitive
routing, routing based on interactive versus batch traffic, and routing based on dedicated links.
To enable policy routing, you must identify which route map to use for policy routing and create the route
map. The route map itself specifies the match criteria and the resulting action if all of the match clauses
are met. These steps are described in the following task tables.
To enable policy routing on an interface, indicate which route map the router should use by using the
following command in interface configuration mode. A packet arriving on the specified interface will be
subject to policy routing except when its destination IP address is the same as the IP address of the
router’s interface. This command disables fast switching of all packets arriving on this interface.
To define the route map to be used for policy routing, use the following command in global configuration
mode:
Command Purpose
Router(config-if)# ip policy route-map map-tag
Identifies the route map to use for policy routing.
Command Purpose
Router(config)# route-map map-tag [permit | deny]
[sequence-number]
Defines a route map to control where packets are output.