FortiOS operating modes allow you to change the configuration of your FortiGate unit depending on the role it needs to fill in your network.
NAT/Route operating mode is the standard mode where all interfaces are accessed individually, and traffic can be routed between ports to travel from one network to another.
In transparent operating mode, all physical interfaces act like one interface. The FortiGate unit essentially becomes a bridge — traffic coming in over any interface is broadcast back out over all the interfaces on the FortiGate unit.
In transparent mode, there is no entry for routing at the main level of the menu on the web-based manager display as there is in NAT/Route mode. Routing is instead accessed through the network menu option.
To view the routing table in transparent mode, go to System > Network > Routing Table.
When viewing or creating a static route entry in transparent mode there are only three fields available.
|Destination IP / Mask||The destination of the traffic being routed. The first entry is attempted first for a match, then the next, and so on until a match is found or the last entry is reached. If no match is found, the traffic will not be routed.
Use 0.0.0.0 to match all traffic destinations. This is the default route.
|Gateway||Specifies the next hop for the traffic. Generally the gateway is the address of a router on the edge of your network.|
|Priority||The priority is used if there is more than one match for a route. This allows multiple routes to be used, with one preferred. If the preferred route is unavailable the other routes can be used instead.
Valid range of priority can be from 0 to 4 294 967 295.
If more than one route matches and they have the same priority it becomes an ECMP situation and traffic is shared among those routes. See Transparent mode static routing.
When configuring routing on a FortiGate unit in transparent mode, remember that all interfaces must be connected to the same subnet. That means all traffic will be coming from and leaving on the same subnet. This is important because it limits your static routing options to only the gateways attached to this subnet. For example, if you only have one router connecting your network to the Internet then all static routing on the FortiGate unit will use that gateway. For this reason static routing on FortiGate units in transparent mode may be a bit different, but it is not as complex as routing in NAT/Route mode.