A common use for subinterfaces is forwarding a public subnet. A subinterface may be created to support a subnet forwarded through the system. When forwarding a subnet through the system, it is necessary to assign an address for the subnet to act as the system subnet gateway. To configure forwarding rules, choose Network > NAT > Port Forwarding and refer to Configuring Port Forwarding.
When applied to the WAN/Provider interface, these addresses are protected by the same firewall policy that is applied to the WAN/Provider address. Other features in the system automatically create Subinterfaces, refer to Configure NAT Settings.
When viewing the Network > Network Information page, Subinterfaces are designated in the Interface Information section with the device name and number, separated by a colon (for example, eth0:100 or eth0.1:100). Refer to View Network Information.
After creating a LAN subinterface, it is often necessary to configure a firewall forwarding rule to permit IP packets through the system. Refer to Configure Basic WAN Firewall Settings.