There are four core types of NAT:

• Full Cone NAT: Any external address and port may access an internal resource as long as the internal resource is contacted first
• Restricted Cone NAT: An external IP address can connect to an internal resource only if it has previously interacted with it
• Port Restricted Cone NAT: Only if an external IP address and port has interacted through that port with the internal resource it has the accessibility on the external address and port
• Symmetric NAT: When packets are sent to an external IP address and port, while being replied from the same, different handles will be provided to the external IP address and port. When two different outside users attempt to connect to the same internal address with the same port number, each will receive a different number