NAT (Network Address Translation) is the process of converting a computer's IP address into another IP address for routing data packets across a network. There are four main types of NAT:
Full Cone NAT: Each external address and port can access an internal resource provided it initiates communication first
Restricted Cone NAT: An external address and port can access an internal resource only if it has previously communicated with that resource
Port Restricted Cone NAT: An external address and port can access an internal resource only if it has previously communicated with that resource through that port
Symmetric NAT: Packets sent to the same external IP address and port will be sent to different external IP addresses and ports. Each external user will get a unique address when they try to connect to the same internal IP address and port
The process of determining NAT type involves checking port availability and the state of the Internet connection to identify which of the four NAT types is being used in the network