As STUN component requires 2 external IP addresses to work properly, it required both (primary and secondary) IP/port configuration.
Only properties with -external- are optional as they are used to specify external IP/port pairs is our STUN server is behind a firewall which forwards traffic but at the same time maps ip address to internal one.
To sum up, looking at an example from documnetation which you added:
Add Stun configuration documentation to component and then to overall documentation.