NAT technology revealed: Do you really understand static NAT, dynamic NAT and PAT?

NAT (Network Address Translation) is crucial in modern network communications. Whether it is an enterprise, home or data center, NAT support is indispensable. Static NAT, dynamic NAT and PAT (Port Address Translation) are the three major mechanisms of NAT, showing unique advantages in different scenarios. Shenchang will take you to understand the principles and differences of NAT technology.

1. What is NAT?
NAT (Network Address Translation) is used to convert private IP addresses to public IP addresses, solve the problem of IPv4 address exhaustion, and improve network security.

The main functions of NAT:

Relieve IPv4 address exhaustion: Allow intranet devices to share a small number of public IP addresses.

Hide intranet topology: Improve intranet security and prevent direct external access.

Increase address reuse rate: Multiple devices share the same public IP address, saving resources.

2. Static NAT
Definition: Static NAT maps a private IP address to a public IP address, and the address mapping relationship remains unchanged.


Working principle:

When the internal host accesses the external network, it uses a fixed public IP for communication.
When the external host accesses the internal host through this public IP, the NAT device will request back to the corresponding internal network address.
Common application scenarios:

Web servers, mail servers and other services that require external access.
Equipment or system that requires a fixed public IP address.
Pros and cons comparison:

Pros: Fixed address, fast access speed, suitable for scenarios where services are provided externally.
Disadvantages: Consumes a large number of public IP addresses, low security, and easy to be attacked.



3. Dynamic NAT
Definition: Dynamic NAT uses an address pool (IP Pool) to dynamically map multiple private IP addresses to one or more public IP addresses.

Working principle:

When an internal host initiates access, the NAT device selects a public IP from the address pool for mapping.

After the connection ends, the public IP is released and can be used by other hosts.
Common application scenarios:

Enterprise networks need to temporarily allocate public IPs for access.
There are many internal devices, but no fixed public addresses are required.
Advantages and disadvantages comparison:


Advantages: Improve public IP resource utilization, and dynamic address allocation is more flexible.
Disadvantages: When the address pool IP is exhausted, new sessions cannot be established.

4. PAT (Port Address Translation)
Definition: PAT (Port Address Translation), also known as NAT Overload, maps multiple private IP addresses to the same public IP through different ports.

Working principle:

When the intranet host accesses the Internet, the NAT device converts the IP address + port number to a public IP address + a different port number.
When returning data, the recorded port number is used to map back to the correct internal host.
Common application scenarios:



Home routers and enterprise gateways are suitable for environments where a large number of internal network users share public IPs.
When a large number of users access the external network at the same time.
Advantages and disadvantages comparison:

Advantages: Greatly improve the utilization rate of public IP resources, suitable for large-scale user access scenarios.
Disadvantages: Some port-sensitive applications may cause communication abnormalities due to port reuse.

5. Differences