How does a NAT firewall prevent external scanning attacks?

A NAT (Network Address Translation) firewall prevents external scanning attacks by hiding internal IP addresses and controlling inbound traffic. Here's how it works:

1. IP Address Masquerading: NAT translates private (internal) IP addresses into a single public IP address when devices access the internet. External attackers only see the public IP, not the actual internal IPs of devices behind the NAT. This makes it difficult to scan or target specific internal systems.

2. Inbound Traffic Filtering: By default, NAT firewalls block unsolicited incoming traffic unless explicitly allowed (e.g., for a specific service like a web server). This prevents attackers from scanning open ports on internal devices since those ports are not directly exposed.

3. Stateful Inspection: Modern NAT firewalls track active connections. They only allow return traffic for established sessions, blocking random scans or unauthorized connection attempts.

Example:

• A company has 100 employees with private IPs (e.g., 192.168.1.1–100). The NAT firewall assigns them a single public IP (e.g., 203.0.113.5).
• An attacker scans 203.0.113.5 for open ports. The NAT firewall only exposes necessary services (e.g., port 443 for a web app) and drops scans targeting other ports (e.g., port 22 for SSH on internal devices).
• Even if the attacker finds an open port, they can’t directly reach internal IPs because NAT obscures them.

Recommended Tencent Cloud Service:
For enhanced protection, use Tencent Cloud NAT Gateway combined with Security Group and Network ACL rules to control traffic. Additionally, Tencent Cloud Anti-DDoS and Web Application Firewall (WAF) can further mitigate scanning and attack risks.