why STUN doesn't work with symmetric NAT? I read this line from wikipedia. > " ** _STUN does work with three types of NAT: full cone NAT, restricted cone NAT, and port restricted cone NAT**. In the cases of restricted cone or port restricted cone NATs, the client must send out a packet to the endpoint before the NAT will allow packets from the endpoint through to the client. **STUN does not work with symmetric NAT_** " Can anyone explain why?

Because STUN(external server), cant know which port will be given to the client by NAT-device. In symmetric NAT, client gets unique port(ip:port in pool situation) on each connection