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Configuring PBR
Introduction to PBR
Policy-based routing (PBR) uses user-defined policies to route packets. A policy can specify the next hop
for packets that match specific criteria such as ACLs.
A device forwards received packets using the following process:
1. The device uses PBR to forward matching packets.
2. If the packets do not match the PBR policy or the PBR-based forwarding fails, the device uses the
routing table, excluding the default route, to forward the packets.
3. If the routing table-based forwarding fails, the device uses the default next hop or default output
interface defined in PBR to forward packets.
4. If the default next hop or default output interface-based forwarding fails, the device uses the default
route to forward packets.
PBR includes local PBR and interface PBR:
• Local PBR guides the forwarding of locally generated packets, such as the ICMP packets generated
by using the ping command.
• Interface PBR guides the forwarding of packets received on an interface only.
Policy
A policy includes match criteria and actions to be taken on the matching packets. A policy can have one
or multiple nodes as follows:
• Each node is identified by a node number. A smaller node number has a higher priority.
• A node contains if-match and apply clauses. An if-match clause specifies a match criterion, and an
apply clause specifies an action.
• A node has a match mode of permit or deny.
A policy matches nodes in priority order against packets. If a packet matches the criteria on a node, it
is processed by the action on the node. Otherwise, it goes to the next node for a match. If the packet does
not match the criteria on any node, it is forwarded according to the routing table.
if-match clause
PBR supports the if-match acl clause to set an ACL match criterion. You can specify only one if-match acl
clause for a node.
apply clause
PBR supports the apply next-hop clause to set next hops for packets.
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