Administrator Guide

Policy-based Routing (PBR)

Overview

When a router receives a packet, the router decides where to forward the packet based on the destination address in the packet, which is

used to look up an entry in a routing table. However, in some cases, there may be a need to forward the packet based on other criteria:

size, source, protocol type, destination, and so on. For example, a network administrator might want to forward a packet that uses

transmission control protocol (TCP) across a different next-hop than packets using Internet control message protocol (ICMP). In these

situations, you can a configure switch route packet according to a policy applied to interfaces.

In another scenario, when the packet comes from one source and wants to go to another destination, then route it to this next-hop or

onto that specific interface. This permits routing over different links or towards different networks even while the destination is the same

but depending on where the packet originates.

To enable PBR, create a redirect list. Redirect lists are defined by rules or routing policies. You can define following parameters in routing

policies or rules:

• IP address of the forwarding router (next-hop IP address)

• Protocol as defined in the header

• Source IP address and mask

• Destination IP address and mask

• Source port

• Destination port

• TCP Flags

After you apply a redirect-list to an interface, all traffic passing through it is subjected to the rules defined in the redirect-list.

Traffic is forwarded based on the following:

• Next-hop addresses are verified. If the specified next hop is reachable, traffic is forwarded to the specified next-hop.

• If the specified next-hops are not reachable, the normal routing table is used to forward the traffic.

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