According to:
https://en.wikipedia.org/wiki/Network_address_translation
there are 4 types of NAT configurations:
Full-cone, Address restricted, Port restricted, and Symmetric.
Now, suppose we have client A and client B on separate networks and are hidden behind their own separate NATs.
What combinations of "client A NAT type" + "client B NAT type" would require a TURN server to be involved (i.e. not solvable by the STUN protocol) if they want to p2p communicate?
For example, I would suspect:
" client A NAT = Symmetric + client B NAT = Symmetric " would require a TURN server.
What are the rest of the combinations?