NAT and PAT Overview

Understanding Network Address Translation (NAT): Principles, Types, and Implementation

Introduction to NAT

Network Address Translation (NAT) is a crucial networking technique that allows multiple devices on a private network to connect to the internet using a single public IP address. Initially developed as a method of mapping one IP address space into another by modifying network address information in the IP header of packets while in transit across a traffic routing device, NAT has evolved to become an essential tool in conserving global address space amid IPv4 address exhaustion. Wikipedia

The Problem NAT Solves

IPv4 addressing scheme allows for approximately 4.3 billion unique addresses (2^32), which is insufficient for the number of devices connected to the internet today. GeeksforGeeks By 1992, it became evident that the IPv4 addressing space would not be enough, and by 1994, NAT was proposed as a "short-term solution" to address depletion and routing scalability challenges. Wikipedia

Today, with an estimated 5.35 billion users actively on the internet (and many users having multiple connected devices), the need for address conservation is more important than ever. HowStuffWorks

How NAT Works

NAT operates at the network layer (Layer 3) of the OSI model, primarily functioning on routers and firewalls. The translation process involves several key steps: Timus

1. Packet Entry: A device within a private network sends a data packet to a NAT-enabled router.

2. IP Address Translation: The router modifies the source IP address from private to public.

3. Transmission: The modified packet is sent to its destination on the internet.

4. Response Handling: When the destination server responds, the packet arrives at the NAT router with the public IP address.

5. Reverse Translation: The router translates the destination IP address from public back to the private IP of the original requesting device.

6. Packet Delivery: The packet is forwarded to the device within the private network.

This process works similarly to many organizations' phone systems: the company publishes a single public number, and once a customer calls, they are transferred to a specific internal extension based on their request. Check Point Software

Types of NAT

There are several types of NAT implementations, each serving different needs:

1. Static NAT

Static NAT maps an internal IP address to an external one on a one-to-one basis. HowStuffWorks This type doesn't help with IPv4 scalability but makes a system reachable from outside the network without disrupting internal addressing schemes. Check Point Software This is the type of NAT we'll implement in our lab exercise below.

2. Dynamic NAT

With Dynamic NAT, a firewall has a pool of external IP addresses that it assigns to internal computers as needed, creating a one-to-one mapping that isn't permanent. HowStuffWorks

3. Port Address Translation (PAT)

PAT creates many-to-one mappings between internal and external IP addresses. The firewall uses the same IP address for multiple systems but assigns a different TCP or UDP port to each connection. Check Point Software This is the most common type of NAT and has become synonymous with the term NAT in common usage. Wikipedia

PAT is also known as NAT overload or overloading, where many local (private) IP addresses can be translated to a single registered IP address using port numbers to distinguish the traffic. GeeksforGeeks

4. NAT64

NAT64 is an IPv6 transition technology that supports the translation of an IPv6 network address into an IPv4 address, with both stateless and stateful versions available. Cisco

Benefits of NAT

NAT provides several critical advantages:

1. IP Address Conservation: By allowing multiple devices to share a single public IP address, NAT conserves valuable IPv4 addresses. Timus

2. Enhanced Security: NAT hides the internal IP addresses of devices, making it more difficult for external attackers to target specific devices on a network. Timus

3. Network Flexibility: NAT facilitates the integration of private networks with the public Internet, allowing for seamless communication and resource sharing. Timus

4. Load Balancing: NAT can distribute incoming traffic across multiple servers, enhancing the performance and reliability of services. Timus

Private IP Address Ranges

For all NAT configurations, organizations can use private IP addresses within their local area networks (LANs). The IPv4 ranges designated for internal use only are:

• 10.0.0.0/8

• 172.16.0.0/12

• 192.168.0.0/16 Check Point Software

These addresses are not routable outside of the organization's network and must be translated by NAT to communicate with the internet.