Network Address Translation (NAT)

Network Address Translation (NAT) is a technique used in computer networking that allows devices on a local network to communicate with devices on external networks, such as the Internet. NAT allows a single IP address to serve as a proxy for a group of devices, conserving the limited number of publicly routable IP addresses available.

Purpose and Usage

The primary purpose of NAT is to conserve IPv4 addresses, which are the most commonly used IP addresses for communication between devices on the Internet. IPv4 addresses are 32-bit numbers, of which there are only 4.3 billion possible combinations. With the proliferation of devices, such as smartphones, tablets, and Internet of Things (IoT) devices, the number of IPv4 addresses available is becoming increasingly scarce. NAT allows a single public IP address to represent multiple devices on a local network, thereby reducing the number of public IP addresses required.

In addition to conserving IPv4 addresses, NAT also provides an additional layer of security for a local network. When a device on a local network sends a request to an external network, the request is sent to the NAT device, which then forwards the request to the external network on behalf of the device. The external network only sees the public IP address of the NAT device and not the IP address of the local device. This prevents external networks from directly communicating with devices on the local network, protecting the local network from unauthorized access.

NAT is commonly used in residential and small business networks that have a single public IP address. In these networks, a NAT device is typically integrated into the router that connects the local network to the Internet. The NAT device is responsible for translating the IP addresses of devices on the local network to the public IP address of the router.

Types of NAT

There are several different types of NAT, each with its own specific purpose and usage.

Static NAT

Static NAT is the simplest form of NAT, where a one-to-one mapping is created between a public IP address and a private IP address. This type of NAT is commonly used in situations where a public IP address needs to be permanently assigned to a device on a local network, such as a web server.

Dynamic NAT

Dynamic NAT is a type of NAT where a pool of public IP addresses is assigned to devices on a local network on a temporary basis. When a device sends a request to an external network, the NAT device assigns an available public IP address to the device from the pool. Once the session is complete, the public IP address is returned to the pool and made available for other devices to use.

Port Address Translation (PAT)

Port Address Translation (PAT), also known as Network Address Port Translation (NAPT), is a type of NAT that allows multiple devices on a local network to share a single public IP address. PAT works by assigning a unique port number to each device on the network. When a device sends a request to an external network, the NAT device translates the private IP address of the device to the public IP address of the NAT device and also assigns a unique port number that maps to the private IP address of the device. This allows multiple devices on the local network to share a single public IP address. PAT is commonly used in residential and small business networks that have a single public IP address.

Carrier-Grade NAT (CGNAT)

Carrier-Grade NAT (CGNAT), also known as Large-Scale NAT (LSN), is a type of NAT that is used by Internet Service Providers (ISPs) to conserve IPv4 addresses. CGNAT works by assigning a public IP address to a group of devices on a local network, similar to how PAT works, but on a much larger scale. This allows the ISP to serve many customers with a limited number of public IP addresses. CGNAT can also provide an additional layer of security for the local network, as the public IP address assigned to the group of devices is shared by multiple customers.

Limitations of NAT

While NAT provides a number of benefits, it also has some limitations. One limitation is that it can interfere with some network protocols, such as those that require a direct connection between two devices, such as Virtual Private Networks (VPNs) or peer-to-peer (P2P) file sharing. Additionally, NAT can cause issues with network address translation if different devices on the network have the same IP address, as the NAT device may not be able to distinguish between the devices. Finally, NAT can introduce additional latency into network communications, as each request must pass through an additional layer of translation.