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Port Address Translation

Definition of Port Address Translation

Port Address Translation (PAT), also known as Network Address Port Translation (NAPT), is a technique used in computer networking to map multiple private IP addresses to a single public IP address. It operates at the transport layer of the OSI model, translating the port numbers of incoming and outgoing packets along with their IP addresses.

Origin of Port Address Translation

PAT was developed to address the issue of IPv4 address exhaustion. With the rapid growth of the internet and the limited availability of IPv4 addresses, PAT emerged as a solution to conserve public IP addresses by allowing multiple devices within a private network to share a single public IP address.

Practical Application of Port Address Translation

One practical application of PAT is in home or office networks where multiple devices such as computers, smartphones, and IoT devices need to access the internet simultaneously. By using a PAT-enabled router, these devices can share the same public IP address while maintaining individual communication sessions. This allows for efficient utilization of available IP addresses and facilitates secure communication between the internal network and external servers.

Benefits of Port Address Translation

Address Conservation: PAT enables organizations to conserve public IP addresses by allowing multiple devices to share a single IP address.

Enhanced Security: By masking internal IP addresses from external networks, PAT provides an additional layer of security, making it harder for attackers to directly access internal devices.

Simplified Network Management: With PAT, network administrators can easily manage a large number of internal devices without the need for assigning and tracking individual public IP addresses.

Cost Savings: By reducing the demand for public IP addresses, PAT helps organizations save costs associated with acquiring and maintaining additional IP address space.


NAT (Network Address Translation) translates private IP addresses to public IP addresses, while PAT (Port Address Translation) extends this functionality by also translating port numbers, allowing multiple devices to share a single public IP address using different port numbers.

Some applications, particularly those using protocols like FTP or SIP that embed IP addresses within data payloads, may encounter issues with PAT. However, modern PAT implementations often include Application Layer Gateways (ALGs) to address such compatibility issues.

In general, PAT has minimal impact on network performance. However, excessive port translation can lead to port exhaustion, resulting in dropped connections. Properly configuring PAT parameters and monitoring network traffic can help mitigate such issues.


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