Firewall policy look up
In Transparent mode, like in NAT mode, a firewall policy look up is based on the source and destination interfaces. The matching firewall policy will tell which actions to apply to the traffic, including logging and security scanning.
The FortiGate proceeds as follows to look for a matching firewall policy in Transparent mode:
- Step 1: an Ethernet IP frame ingresses a port (or a VLAN on a port), corresponding to a specific bridge instance (from the port VDOM and Forwarding domain). This frame contains a destination MAC address that we will call MAC_D.
- Step 2: The FortiGate is making a MAC_D address lookup in the bridge instance to determine the port where MAC_D has been learned. This will be the destination interface.
- Step 3: The FortiGate is then looking for a firewall policy corresponding to the couple < source interface + destination interface >. If multiple policies with the same couple < source interface + destination interface > exist, the FortiGate screens all of them from TOP to BOTTOM (as displayed in the configuration), until a match is found. It is important to make sure that the most specific firewall policies are located at the top of the policy list, to make sure that traffic is matched to the appropriate policy.