Technical Note: How resolve the public hostname of a FortiGate captive portal to an internal IP

[FortiKoala]

Description

This article describes how the hostname of the public captive portal can be resolved to the local intern IP address on the FortiGate SSID.

Solution
The captival portal has a hostname of "fortinet-portal.company.abc" this will resolve to a public IP address.  The local FortiGate interface IP address is 20.20.20.1.

Add a new static DNS entry on the FortiGate to resolve fortinet-portal.company.abc to 20.20.20.1 -  see related article

On the FortiGate CLI change portal address from 10.20.20.1 to fortinet-portal.company.abc

config firewall auth-portal
    set portal-addr "fortinet-portal.company.abc"
end

Add Wifi interface address (20.20.20.1) as DNS server on the SSID along side the global DNS server

DNS server settings - x.x.x.x,8.8.8.8 (x.x.x.x = Wireless interface IP address)