Sophos – P5 How to Configure NAT Rules Open Port on Sophos Firewall (Step-by-Step Guide)

Open Port on Sophos Firewall (Step-by-Step Guide)

When deploying public services such as websites, proxy servers, or mail servers, Network Address Translation (NAT) plays a critical role. Properly configuring NAT ensures external users can access internal services securely and correctly.

In this tutorial, you will learn how to Configure NAT Rules Sophos to open ports and publish internal servers to the internet.

This guide covers:

1. Demo NAT port 80/443 for VM 192.168.16.175 (Proxy)

2. Demo NAT ports for Email Server VM 192.168.16.172

The configuration approach shown here can be reused for other services such as:

• IP Cameras

• Web Applications

• Internal Websites

• Application Servers

• Remote Access Services

Let’s go step by step.

1️⃣ Demo NAT Port 80/443 for VM 192.168.16.175 (Proxy)

In this scenario:

Internal Proxy VM IP:
192.168.16.175

Ports to NAT:
80 (HTTP)
443 (HTTPS)

These ports allow public web access to the internal proxy server.

Step 0: Check Port

Before performing NAT, verify:

• The service is running internally

• The VM is reachable from LAN

• Ports 80 and 443 are open on the server

This ensures that NAT troubleshooting later is easier.

Step 1: Create Host and Service

Create a host object for:

192.168.16.175

Then create or verify service definitions for:

Port 80
Port 443

This ensures clean object-based configuration and better rule management.

Step 2: Perform NAT

Proceed to configure DNAT (Destination NAT).

DNAT will generate 3 NAT rules.

After completing the NAT configuration, Sophos will automatically generate a similar firewall rule.

This firewall rule allows the translated traffic to reach the internal server.

Important:

Always verify that the generated firewall rule is correctly placed in rule order.

At this stage, port 80 and 443 are published externally.

The process is similar when needing to NAT ports for other services such as:

• Camera

• Website

• Email Server

• Application Services

Once you understand how to Configure NAT Rules Sophos, publishing services becomes straightforward.

2️⃣ Demo NAT Port for Email Server VM 192.168.16.172

Now let’s publish an internal email server.

Internal VM IP:
192.168.16.172

Required ports:

995
25
465
587
993
7071
7025

These are the necessary ports for Zimbra Mail Server.

Each port serves a specific mail function:

• 25: SMTP

• 465 / 587: Secure mail submission

• 993 / 995: Secure IMAP/POP

• 7071 / 7025: Administrative and service ports

NAT Configuration Process

The NAT configuration process is identical to the previous example:

Step 0: Check service availability internally

Step 1: Create host and required service objects

Step 2: Perform DNAT

DNAT will generate corresponding NAT rules.

Completing NAT will also generate the related firewall rule automatically.

Ensure:

• NAT rules are correctly mapped

• Firewall rule allows WAN to LAN

• No conflicting rules exist

Once configured, external mail clients can connect to your Zimbra server.

Why Ports 80 and 443 Do Not Require NAT in This Setup

In this demo system, ports 80 and 443 are not directly NATed for the email server.

Reason:

I am using a proxy server (192.168.16.175) as the central hub for internal port forwarding.

The proxy acts as an intermediary layer between the internet and internal services.

This architecture provides:

🔹 Centralized SSL handling
🔹 Reverse proxy capability
🔹 Improved security segmentation
🔹 Simplified certificate management

Proxies are very powerful tools for securing systems and public services on the internet.

A dedicated video will demonstrate this feature in detail.

Best Practices When You Configure NAT Rules Sophos

To maintain a secure and professional deployment:

✅ Verify internal service before NAT

Never troubleshoot external access before confirming LAN access works.

✅ Use object-based configuration

Always create host and service objects.

✅ Keep NAT documentation

Document public IP to internal IP mapping.

✅ Monitor firewall logs

Check live logs during testing.

✅ Avoid unnecessary open ports

Only publish required services.

Common Mistakes to Avoid

❌ Forgetting firewall rule validation
❌ Opening incorrect service ports
❌ NAT rule placed in wrong order
❌ Testing without checking internal service
❌ Ignoring ISP port blocking policies

Careful planning ensures stable public service exposure.

When Should You Configure NAT Rules Sophos?

You should configure NAT when:

• Hosting a website internally

• Publishing email server

• Allowing external camera access

• Deploying application services

• Enabling remote access systems

NAT is fundamental for bridging private and public networks securely.

Conclusion

In this guide, you learned how to Configure NAT Rules Sophos to open ports and publish internal services.

You have successfully:

• NATed ports 80 and 443 for proxy VM 192.168.16.175

• NATed required mail ports for VM 192.168.16.172

• Understood how DNAT generates NAT and firewall rules

• Recognized the role of proxy in advanced deployments

Mastering how to Configure NAT Rules Sophos allows you to securely expose internal services to the internet with full control.

In the next phase, you can extend this configuration with:

• Advanced reverse proxy

• SSL offloading

• Web server protection

• IPS policies

Your Sophos Firewall is now capable of handling professional-grade service publishing. 🔐🚀