© Copyright Lenovo 2016 Chapter 27: Policy-Based Routing 445Configuring Route MapsA route map is used to control and modify routing information. When PBR isenabled on an interface, all incoming packets are filtered based on the criteriadefined in the route maps. For packets that match the filtering criteria, theprecedence or Differentiated Services Code Point ( DSCP) value can be changed, orthe packets can be routed/forwarded to the appropriate next hop.PBR and dynamic routing protocols, such as Border Gateway Protocol (BGP) andOpen Shortest Path First (OSPF), use route maps. You can define a maximum of255 route maps. Route maps used by a PBR policy cannot be used by a dynamicrouting protocol. You can configure a maximum of 32 access list statements in aroute map. You can assign only one route map to a non‐management IP interface.You must define route map criteria using match and set commands. Allsequential match clauses must be met by the packets for the set clauses to beapplied.Match ClausesIPv4 ACLs can be used to specify the match criteria. The following match criteriacan be used in a PBR ACL: Source IP Destination IP Protocol ToS TCP/UDP source port TCP/UDP destination portIf criteria other than the above are used in a PBR ACL, the switch will display anerror message.If ingress packets do not meet any of the match criteria, or if a deny statement isconfigured in the ACL, then the packets are routed based on the entries in therouting table.Set ClausesWhen the match clause(s) is satisfied, one of the following set clauses can be usedto specify the packet forwarding criteria: Next hop IP address: This must be the IP address of an interface on the adjacentrouter. A remote router interface cannot be used to specify the next hop. Packetsare forwarded to the next hop IP address. The PBR policy uses the next hops inthe order you specify. If the first next hop is down, then the second next hop isused, and so on. If you specify the next hop addresses using separate statements,then the next hops are used in the order you specify, starting from top to down.A maximum of 64 unique next hops can be configured across all route maps. IP Differentiated Services Code Point (DSCP) value: A value used to set theDSCP value of the matching packets.
