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NAT & PAT

Network Address Translation (NAT)​

NAT is a method used in networking that allows one set of IP addresses to be remapped to another set by modifying network address information in the IP header of packets while they are in transit across a traffic routing device. This technique is most commonly used to translate private (non-routable) IP addresses to a public IP address or addresses.

Purpose​

  1. Conservation of Public IP Addresses: NAT helps in conserving the limited pool of public IP addresses by allowing multiple devices on a private network to share a single or a few public IP addresses for internet access.

  2. Security: By hiding internal IP addresses from the external network, NAT provides a layer of obscurity, making it harder for attackers to directly access internal network devices.

  3. Network Simplification: NAT simplifies the network by allowing the internal network to use private IP addresses without concern for external routing. This makes internal network changes transparent to the outside world.

Port Address Translation (PAT)​

PAT, often referred to as "NAT overload", is a type of dynamic NAT that maps multiple private IP addresses to a single public IP address (or a few addresses) by using different ports. It's a variant of NAT that extends its capabilities to manage individual sessions, which is especially useful when the number of internal clients exceeds the number of available public IP addresses.

Purpose​

  1. Multiplexing Multiple Connections: PAT allows multiple internal devices to simultaneously access external networks using a single public IP address. It distinguishes different sessions by assigning unique source port numbers to each session's packets.

  2. Efficient Use of IP Addresses: By using different ports for each session, PAT enables extensive sharing of a limited number of public IP addresses among many internal users, optimizing the utilization of available IP addresses.

  3. Enhanced Privacy and Security: Similar to NAT, PAT also hides the internal structure of a private network from the public internet, adding an additional layer of privacy and security.

How They Work Together​

  • Operation: In a typical home or small business network, a router or firewall performs NAT/PAT to allow devices on the private network to access the internet. When an internal device initiates a connection to the internet, the router translates the internal IP address to the public IP address assigned to it. With PAT, it also translates the source port number to a unique port number to keep track of the session.

  • Example Scenario: Consider a home network where multiple devices need to access the internet, but the ISP provides only one public IP address. The router uses NAT to translate the private IP addresses of these devices to the single public IP address. Using PAT, it assigns a unique port number to each outgoing connection, allowing multiple devices to share the public IP address without conflict.

Conclusion​

NAT and PAT are fundamental technologies in IP networking that address the limitations of IP address availability and offer a layer of security for private networks. While NAT focuses on the translation of IP addresses, PAT extends this by managing port numbers to support multiple connections through a single IP address. Together, they enable efficient and secure use of IP addresses in accessing external networks.