Network Address Translation (NAT)
To access Internet, one public IP address is needed, but we can use private IP address in our private network. The idea of NAT is to allow multiple devices to access Internet through a single public address. To achieve this, translation of private IP address to a public IP address is required.
Network Address Translation (NAT) is a process in which one or more local IP address is translated into one or more Global IP address and vice versa in order to provide Internet access to the local hosts. Also, it does the translation of port numbers i.e. masks the port number of the host with another port number, in the packet that will be routed to destination. It then makes the corresponding entries of ip address and port number in the NAT table. NAT generally operates on router or firewall.
Network Address Translation (NAT) working
Generally, the border router is configured for NAT i.e the router which have one interface in local (inside) network and one interface in global (outside) network. When a packet traverse outside the local (inside) network, then NAT converts that local (private) IP address to a global (public) IP address. When a packet enters the local network, the global (public) IP address is converted to local (private) IP address.