The rules that define policy routing are as follows:
• Traffic can be directed on either the source address or both the source and destination addresses.
• Policy routing affects only the routing of the router on which it is configured in determining the next hop in the path to the destination.
• Policy routing does not affect the destination of the packet.
• Policy routing does not allow traffic sent into another autonomous system to take a different path from the one that would have been chosen by that autonomous system.
• It is possible only to influence how traffic will get to a neighboring router.
• As policy routing examines the source address, it is configured on the inbound interface.
Route maps were introduced in Cisco IOS Release 11.0, allowing policies that defined different paths for different packets based on defined criteria.
Policy-based routing also provides a mechanism to mark packets with different types of service (TOS). This feature can be used in conjunction with Cisco IOS queuing techniques so that certain kinds of traffic can receive preferential service.
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