To send network traffic, a router usually examines the destination address in the packet and looks at the routing table to find the next-hop destination. In some cases, you want to send traffic to a different path than the default route specified in the routing table. You can configure a policy with a specific external interface to use for all outbound traffic that matches that policy. This technique is known as policy-based routing. Policy-based routing takes precedence over other multi-WAN and virtual BOVPN interface settings.
Policy-based routing can be used when you have more than one external interface and have configured your XTM device for multi-WAN or if you configure a virtual BOVPN interface. With policy-based routing, you can make sure that all traffic for a policy always goes out through the same external interface, even if your multi-WAN or virtual BOVPN interface configuration is set to send traffic in a round-robin configuration. For example, if you want email to be routed through a particular interface, you can use policy-based routing in the SMTP-proxy or POP3-proxy definition.
To use policy-based routing, you must have Fireware XTM with a Pro upgrade. You must also configure at least two external interfaces.
When you use policy-based routing with multi-WAN failover, you can specify whether traffic that matches the policy uses another external interface when failover occurs. The default setting is to drop traffic until the interface is available again.
Failback settings (defined on the Multi-WAN tab of the Network Configuration dialog box) also apply to policy-based routing. If a failover event occurs, and the original interface later becomes available, the XTM device can send active connections to the failover interface, or it can fail back to the original interface. New connections are sent to the original interface.
If you select a virtual BOVPN interface for policy-based routing, the failover and failback settings are not available.
You can set the interface you specified for this policy as the primary interface, and define other external interfaces as backup interfaces for all non-IPSec traffic. If the primary interface you set for a policy is not active, traffic is sent to the backup interface or interfaces you specify.
About Using Multiple External Interfaces
About Policy Properties