How does FortiGate select the central SNAT policy that is applied to a TCP session?

While an outgoing interface is a criterion for matching a central SNAT policy, the SNAT policy itself is not configured directly on the interface but rather within the central SNAT policy list.

FortiGate processes central SNAT policies in a top-down manner, similar to firewall policies, applying the very first policy that matches the source, destination, service, and outgoing interface of the TCP session.

FortiGate SNAT policies do not use a separate priority system; instead, their processing order is determined by their position in the policy list (top-down evaluation).

In central NAT mode, SNAT is explicitly handled by central SNAT policies, not by settings within the firewall policy that matches the traffic, which is the behavior for interface-based NAT.