3.3.j Implement optimize and troubleshoot policy-based routing

PBR gives you a flexible means of routing packets by allowing you to configure a defined policy for traffic flows, lessening reliance on routes derived from routing protocols. To this end, PBR gives you more control over routing by extending and complementing the existing mechanisms provided by routing protocols. PBR allows you to set the IP precedence. It also allows you to specify a path for given type of traffic.

You can set up PBR as a way to route packets based on configured policies. For example, you can implement routing policies to allow or deny paths based on the identity of a particular end system, an application protocol, or the size of packets. PBR allows you to perform the following tasks:

● Classify traffic based on extended access list criteria. Access lists, then, establish the match criteria.

● Set IP Precedence bits, giving the network the ability to enable differentiated classes of service.

● Route packets to specific traffic-engineered paths; you might need to route them to allow a specific QoS through the network.

Policies can be based on IP addresses, port numbers, protocols, or size of packets.

Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Location 2796).  . Kindle Edition.

http://www.cisco.com/c/en/us/td/docs/ios/12_2/qos/configuration/guide/fqos_c/qcfpbr.html