BigIron RX Series Configuration Guide 56353-1001810-01Chapter22Policy-Based RoutingIn this chapter• Policy-Based Routing (PBR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563• Configuration considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 563• Configuring a PBR policy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 564• Configuration examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 567• Trunk formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 569Policy-Based Routing (PBR)Policy-Based Routing (PBR) allows you to use ACLs and route maps to selectively modify and routeIP packets in hardware. The ACLs classify the traffic. Route maps that match on the ACLs setrouting attributes for the traffic.A PBR policy specifies the next hop for traffic that matches the policy. Using standard ACLs withPBR, you can route IP packets based on their source IP address. With extended ACLs, you canroute IP packets based on all of the clauses in the extended ACL.You can configure the device to perform the following types of PBR based on a packet’s Layer 3 andLayer 4 information:• Select the next-hop gateway.• Send the packet to the null interface (null0).When a PBR policy has multiple next hops to a destination, PBR selects the first live next hopspecified in the policy that is up. If none of the policy's direct routes or next hops are available, thepacket is routed in the normal way.Configuration considerations• A PBR policy on an interface takes precedence over a global PBR policy.• You cannot apply PBR on a port if that port already has ACLs, ACL-based rate limiting, orTOS-based QoS.• The number of route maps that you can define is limited by the system memory. When a routemap is used in a PBR policy, the PBR policy uses up to 6 instances of a route map, up to 6 ACLsin a matching policy of each route map instance, and up to 6 next hops in a set policy of eachroute map instance.• ACLs with the log option configured should not be used for PBR purposes.
