Network Address Translation (NAT) is the process that modifies the IP address in a header of an IP packet, while it is travelling through a routing device. NAT allows one set of IP addresses to be used for traffic within a LAN (Local Area Network) and another set of IP addresses to be used for outside traffic. One to one transformation of IP addresses are provided by the simplest form of NAT. NAPT (Network Address and Port Translation) is an extension of NAT that allows many IP addresses to be mapped in to a single IP address. This is done with the help of TCP and UDP port information in the outgoing traffic.
What is NAT?
Network Address Translation modifies IP address in a header of an IP packet, while it is travelling through a routing device. NAT allows one set of IP addresses to be used for traffic within a LAN and another set of IP addresses for outside traffic. One to one transformation of IP addresses are provided by the simplest form of NAT. NAT has several advantages. It improves the security of a LAN since it provides the option to hide internal IP addresses. Furthermore, as the IP addresses are only used internally, it will not cause any conflicts with IP addresses used in other organizations. Also, using a single internet connection for all the computers in a LAN is made possible by NAT. NAT works with the use of a NAT box, which is situated in the interface where the LAN is connected to the internet. It contains a set of valid IP addresses and it is responsible for performing the IP address translations.
What is a NAPT?
NAPT (Network Address and Port Translation) is used to map a set of private IP addresses using a single public IP address or a small group of public IP addresses. NAPT is also referred to as PAT (Port Address Translation), IP masquerading, NAT Overload and many-to-one NAT. In NAPT, many IP addresses are mapped to a single IP address. This would cause an ambiguity when routing the returned packets. To avoid this problem NAPT makes use of the TCP/ UDP port information in the outgoing traffic and maintains a translation table. This would allow routing the returned packets correctly to the requester.
What is the difference between NAT and NAPT?
NAT modifies IP address in a header of an IP packet, while it is travelling through a routing device and allows to use a different set of IP addresses to be used for traffic within a LAN than the set of IP addresses used for outside traffic, while NAPT is a special kind of NAT where multiple private IP addresses are mapped in to as single IP or a small group of public IP addresses. Therefore NAPT involves a many-to-one translation of IP addresses. NAPT is the most widely used NAT, therefore most of the time NAPT is referred as NAT.