Types of Network Address Translation (NAT)


NAT is an IETF standard through which several computers or private network devices can share a single IPv4 address. The main reason for the growing popularity of Network Address Translation is an increasing shortage of IPv4 addresses.

There are three basic concepts in address translation:

  • Static (SNAT, Static Network Address Translation)
  • Dynamic (DAT, Dynamic Address Translation)
  • PAT (NAPT, NAT Overload, Port Address Translation)

Static Network Address Translation

Static Network Address Translation (SAT, SNAT) performs one-to-one translation of internal IP addresses to external ones. This allows you to convert the internal network IP to an external IP address. In other words, when passing through a router, the address changes to a strictly specified address, one-to-one. For example, can be replaced by and vice versa.

These mappings are configured by the network administrator and remained constant. When devices send traffic to the internet, their internal local addresses are translated into configured internal global addresses. For external networks, these devices have public IPv4 addresses.

Furthermore, SATs are used when the local host must be accessible from the outside using fixed addresses. It provides connections to both internal and external systems, such as internet hosts. This type of conversion is particularly recommended for sharing the system on the internal network.

Dynamic Network Address Translation

Dynamic NAT differs slightly from static. The essence of it is that several external IP addresses are given by the provider, after which the router itself distributes the addresses according to the need. While static NAT is a constant mapping between inside local and global addresses, dynamic network address translation allows you to automatically map inside local and global addresses (which are usually public IP addresses). Dynamic NAT uses a group or pool of public IPv4 addresses for translation.

As soon as a server or computer wants to go online, the router looks at its list of external addresses issued by the provider, and assign one address from this list, while recording that it has issued such an external address to a server or computer. The life of such a record lasts a very short time, and as soon as the server/computer ceases to require access to the Internet, the address is removed from the router's NAT table.

If the number of local hosts does not exceed the number of public addresses available, each local address will be guaranteed a matching public address. Otherwise, the number of hosts that can simultaneously access external networks will be limited by the number of public addresses. In other words, it would be good for the number of internal addresses to be slightly more than the number of addresses in the pool.

After all, as soon as the router runs out of addresses in the list, it will not be able to start up new computers or servers on the Internet until at least one external address is released. Dynamic NAT uses a pool of public addresses and assigns them according to the "first come, first served" principle.

Port Address Translation

Port and Address Translation (PAT) is a form of dynamic NAT that maps several private addresses to a single public IP address. It is used when the number of clients exceeds the size of the pool of global addresses. PAT allows you to significantly save address space. The ISP assigns one address to the router, but several family members can access the internet at the same time.

The PAT stores the address in the internal global address pool, allowing the router to use one inside global address for many internal local addresses. In other words, a single open IPv4 address can be used for hundreds or even thousands of internal private IPv4 addresses.

With PAT, multiple addresses can be mapped to one or more addresses, since each private address is also tracked by a port number. When a device initiates a TCP/IP session, it generates a TCP or UDP source port value to identify the session. When a NAT router receives a packet from a client, it uses its source port number to identify a specific NAT translation. PAT ensures that devices use a different TCP port number for each session. When the response is returned from the server, the source port number, which becomes the destination port number in the return path, determines which device the router forwards the packets to.

How to choose the type of NAT

Static NAT is particularly useful when a device needs to be accessible from outside the network. This approach isn't used very often because it doesn't save on registering IP addresses and this type of translation results in an IP address that is not shared for other purposes.

Dynamic NAT has two main use cases. The first is to allow for protocols which create a secondary, dynamic connection back to the client. The second is if you need a Bidirectional mapping of Private IPs to Public IPs, but don't particularly care about the explicit mapping between the two.

PAT is one of the most popular types of Network Address Translation. If all the hosts need to use the internet concurrently at the same time, PAT should be used. In this method, even a single public IP address is sufficient to make thousands of hosts to connect to the internet

NFWare virtual Carrier Grade NAT supports all types of Network Address Translation, such as Static, Dynamic, PAT and meets any requirements no matter what type of NAT an operator chooses. Moreover, in addition to NAT44 mode, it also provides NAT64 allowing operators smoothly migrate to IPv6 infrastructure.
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