TLV values for the Option 43 sub-option: Type + Length + Value.

• Type is always the suboption code 0xf1.
• Length is the number of controller management IP addresses times 4 in hex.
• Value is the IP address of the controller listed sequentially in hex.

Convert IP address to Hex:

Open the windows calculator and go to Programmer mode. Ensure DEC mode is selected and type in the first octet of your UniFi Controller’s IP, then see the HEX value displayed. Windows displays the value as a single digit when possible, but when entering it in hexadecimal, it must be 2 digits. Prepend a 0 to any single-digit hex values you get.

 

For example, suppose there are two controllers with management interface IP addresses, 192.168.10.5 and 192.168.10.20. The type is 0xf1. The length is 2 * 4 = 8 = 0x08. The IP addresses translates to c0a80a05 (192.168.10.5) and c0a80a14 (192.168.10.20). When the string is assembled, it yields f108c0a80a05c0a80a14. The Cisco IOS command that is added to the DHCP scope is option 43 hex f108c0a80a05c0a80a14.