8.3 NAT Rules Explained

Key Concepts

• NAT Overview
• Static NAT
• Dynamic NAT
• PAT (Port Address Translation)
• NAT Exceptions

1. NAT Overview

Network Address Translation (NAT) is a method used to modify IP address information in IP packet headers while they are in transit across a traffic routing device. NAT helps in conserving IP addresses, enhancing security, and simplifying network management.

Example: Think of NAT as a post office that changes the return address on a letter before sending it out. This helps in tracking the letter and ensuring it reaches the correct destination.

2. Static NAT

Static NAT involves a one-to-one mapping between private IP addresses and public IP addresses. This type of NAT is commonly used for servers that need to be accessible from the internet.

Example: Consider static NAT as a permanent address change service. Just as a person permanently changes their address, a private IP address is permanently mapped to a public IP address.

3. Dynamic NAT

Dynamic NAT involves a pool of public IP addresses that are dynamically assigned to private IP addresses as needed. This type of NAT is used to conserve public IP addresses and is commonly used in home networks.

Example: Think of dynamic NAT as a hotel reservation system. Just as a hotel assigns rooms to guests as they arrive, dynamic NAT assigns public IP addresses to private IP addresses as needed.

4. PAT (Port Address Translation)

PAT, also known as NAT overload, maps multiple private IP addresses to a single public IP address using different port numbers. This allows multiple devices on a private network to share a single public IP address.

Example: Consider PAT as a call center where multiple agents share a single phone number. Each agent uses a different extension number, allowing multiple calls to be handled simultaneously.

5. NAT Exceptions

NAT exceptions allow certain traffic to bypass NAT rules. This is useful for traffic that needs to retain its original IP addresses, such as VPN traffic or certain types of server communications.

Example: Think of NAT exceptions as a VIP lane at an airport. Just as VIPs bypass the regular security checks, certain types of traffic bypass NAT rules to retain their original IP addresses.