The operation objects of policy-based routing are data packets. Suppose a routing table has been generated; instead of performing forwarding according to the routing table, the method of its forwarding path is changed according to a certain policy as needed. The primary function is to select the outbound interfaces and lines, according to the source/destination IP addresses, source/destination ports, protocols, and other conditions, when the device has multiple WAN interfaces connecting with multiple WAN lines.

The link fault detection function shall be enabled for the interface/zone. See the figure below.