Technical Tip: FortiGate DHCP option 43 controller IP configuration to support FortiWLC AP devices

[fmerin_FTNT]

Description

This article describes the format for DHCP option 43 to specify the controller IP that should be used to support this setup.

The FortiGate can be used as a DHCP server with the FortiWLC AP devices.

Scope

FortiOS v5.4, FortiWLC-SD v7.0-10.

Solution

The following FortiGate CLI configuration could be used to configure the controller IP of 1.2.3.4:

config system dhcp server

    edit 1

        config options
            edit 1
                set code 43
                set type hex
                set value 2b 1a 31 2e 32 2e 33 2e 34
end

FortiAPs or third-party APs need to discover the FortiGate.

By setting up DHCP Option 43 on the DHCP server, APs can automatically find the FortiGate controller’s IP address without manual configuration.

Note on ASCII to HEX conversion above:

• ASCII: +1.2.3.4.
  
  
• HEX: 2b 1a 31 2e 32 2e 33 2e 34.
  
  

The first 2 HEX values are required for the AP to correctly parse/read the HEX value representation of the controller IP.