Hello,

When talking about prefix lists and filter lists, they are both concerned with filtering the routing information in a routing protocol. A prefix list allows you to filter network by their prefix and their netmasks. A filter list is actually an AS-path list and is used in BGP to filter networks based on their AS_PATH attribute.

A route-map is a more general construct that allows you to aggregate several testing criteria, such as access lists, prefix lists, AS-path lists and others with logical AND or OR semantics, and if the item under test passes these criteria, the route-map can apply (or set) a certain attribute on that item. A route-map can be used for filtering networks in routing protocols and setting various attributes, for example, metric, next hop, local preference, weight, AS-path, BGP community and many more. However, a route-map is also used in various other applications such as Policy Based Routing where it is used to override the routing table and direct a flow of selected data packets to a particular next-hop. Another use of route-map is in NAT where it allows to test for certain properties of the packet or its way through the router which would not be possible using plain ACLs (for example, the outgoing interface).

A policy-map is something completely different from the concepts described so far. A policy-map is used to apply certain QoS parameters and treatment to a class of packets. As the name suggests, it maps a set of QoS policies to a class of packets. It is thus used when provisioning QoS.

Best regards,

Peter