NAT technology revealed: Do you really understand static NAT, dynamic NAT and PAT?
Hello everyone, I am Shenchang. I still remember when I was in school and just started learning programming, I ran a very interesting small project locally. I wanted to show it off to my classmates, so I sent them the address 127.0.0.1/navigation, but found that they could not access it. This problem puzzled me for a long time. How can I make a local website that others can visit? Later, after learning about network knowledge, I learned that there are public network addresses, address translation, and internal network penetration.
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 takes everyone 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, solving the problem of IPv4 address exhaustion and improving network security.
The main functions of NAT:
Alleviate 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.
Improve address reuse rate: Multiple devices share the same public IP, 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 map the request back to the corresponding internal network address.
Common application scenarios:
Web servers, mail servers and other services that require external access.
Equipment or systems that require a fixed public IP address.
Advantages and disadvantages comparison:
Advantages: Fixed address, fast access speed, suitable for providing services to the outside world.
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 rights, the NAT device will select a public IP from the address pool to correspond.
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.
Pros and cons comparison:
Pros: Improve the utilization of public IP resources, 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.