Network Address Translation (NAT) Explained

Key Concepts

• Static NAT
• Dynamic NAT
• PAT (Port Address Translation)
• NAT Overload
• NAT Configuration

Static NAT

Static NAT involves a one-to-one mapping between private IP addresses and public IP addresses. This type of NAT is used when a specific private IP address needs to be permanently translated to a specific public IP address. Static NAT is commonly used for servers that need to be accessible from the internet. For example, a web server with a private IP address of 192.168.1.10 can be statically mapped to a public IP address of 203.0.113.10.

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 when multiple private IP addresses need to be translated to a limited number of public IP addresses. Dynamic NAT is commonly used in environments where the number of public IP addresses is limited. For example, a pool of public IP addresses (203.0.113.10-20) can be dynamically assigned to private IP addresses (192.168.1.10-20) as they attempt to access the internet.

PAT (Port Address Translation)

PAT, also known as NAT Overload, allows multiple private IP addresses to be translated to a single public IP address using different port numbers. This type of NAT is used when a single public IP address needs to be shared among many private IP addresses. PAT is commonly used in home networks and small offices. For example, multiple devices in a home network (192.168.1.10-20) can share a single public IP address (203.0.113.10) by using different port numbers for each connection.

NAT Overload

NAT Overload is a specific implementation of PAT where the router uses the source port number to distinguish between different private IP addresses. This allows for efficient use of a single public IP address. NAT Overload is commonly used in scenarios where bandwidth and IP address conservation are critical. For example, a router can use NAT Overload to allow 100 devices in a network to share a single public IP address by using unique source port numbers for each device.

NAT Configuration

NAT configuration involves setting up the NAT rules on a router or firewall. This includes defining the type of NAT (Static, Dynamic, PAT), specifying the private and public IP address ranges, and configuring any necessary access lists. Proper NAT configuration ensures that traffic is correctly translated and routed. For example, configuring a router to use Static NAT for a web server involves specifying the private IP address (192.168.1.10) and the corresponding public IP address (203.0.113.10).

Examples and Analogies

Consider a large office building with multiple departments. Static NAT is like assigning each department a permanent public address that is always used when interacting with the outside world. Dynamic NAT is like having a pool of temporary public addresses that are assigned to departments as needed. PAT is like having a single public address that all departments share, but each department uses a different door (port) to enter and exit the building.

NAT Overload is like the building's security system that uses unique badges (port numbers) for each employee, allowing them to share the same entrance (public IP address). NAT Configuration is like the building manager setting up the rules for who can use which entrance and when, ensuring smooth and secure access for everyone.