PBR issues are independent of IP routing protocols

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Wed, 07/22/2009 - 19:27
Jun 18th, 2009

Core Issue

Troubleshoot your Policy-Based Routing (PBR) issues without including any IP routing protocol information. This is also true for Hot Standby Router Protocol (HSRP) and Network Address Translation (NAT) issues.

Resolution

PBR gives you a flexible means of routing packets. This is done by allowing you to configure a defined policy for traffic flows, thus 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 certain traffic, such as priority traffic over a high-cost link.

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

PBR allows you to perform the following tasks:

  • Classify the traffic based on an extended Access Control List (ACL) criteria. ACLs establish the match criteria.
  • Set IP precedence bits, giving the network the ability to enable the differentiated Classes of Service (CoSs).
  • Route the packets to specific traffic-engineered paths. You might need to route them to allow a specific Quality of Service (QoS) through the network.

Policies can be based on the IP address, port numbers, protocols, or size of the packets. For a simple policy, you can use any one of these descriptors. For a complicated policy, you can use all of them.

To help this tool correctly identify and troubleshoot PBR issues, do not select any IP routing protocols (such as Open Shortest Path First (OSPF), Border Gateway Protocol (BGP), or Enhanced Interior Gateway Routing Protocol (EIGRP)).

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