A NAT (Network Address Translation) firewall manages Internet access shared by multiple devices by translating private IP addresses of devices on a local network into a single public IP address for outbound traffic. This allows multiple devices to share one Internet connection while maintaining security by hiding internal IP addresses from external networks.
How it works:
- IP Address Translation: When a device (e.g., a smartphone or laptop) sends a request to the Internet, the NAT firewall replaces its private IP (e.g., 192.168.1.10) with the router's public IP (e.g., 203.0.113.5).
- Port Mapping: The NAT firewall assigns a unique port number to each outgoing request to track which device initiated the connection. When the response returns, it routes the data back to the correct device.
- Inbound Traffic Blocking: By default, the NAT firewall blocks unsolicited incoming traffic, acting as a basic firewall to prevent external attacks.
Example:
- A home network has three devices: a phone (192.168.1.10), a laptop (192.168.1.20), and a smart TV (192.168.1.30). All share the router’s public IP (203.0.113.5).
- When the phone accesses a website, the NAT firewall translates its request to use the public IP and a unique port (e.g., 203.0.113.5:50000). The response is routed back to the phone using the same port mapping.
- If an external hacker tries to access the smart TV directly, the NAT firewall blocks the request because no internal device initiated the connection.
Tencent Cloud Solution:
For businesses needing secure shared Internet access, Tencent Cloud’s NAT Gateway provides scalable NAT services with built-in security features. It allows multiple cloud servers (like VMs) to share a public IP while maintaining isolation and traffic control. Additionally, Tencent Cloud Security Group and Network ACLs can enhance firewall protection.