Secure Your Router’s Management Interface with DrayTek Port Knocking

When it comes to securing a network, one principle stands above all others: if attackers cannot see a service, they cannot attack it. This is exactly the philosophy behind Port Knocking, a powerful security feature now available on supported DrayTek Vigor routers.

Instead of leaving management ports exposed to the internet, where automated scanners and bots constantly probe for weaknesses, Port Knocking keeps those ports completely closed until an authenticated user performs a specific, time-sensitive “knock” sequence. Only then does the router temporarily open the management interface for access.

In this article, we’ll explore how Port Knocking works, why it matters, and how DrayTek has implemented it to protect your router’s most sensitive entry point: the management interface.

• Keeping all protected ports closed by default
• Requiring a user to “knock” using a specific port sequence
• Validating the knock using TOTP (Time-Based One-Time Passwords)
• Opening the port only for the authenticated user’s IP address

This means attackers scanning your router’s WAN IP address will find nothing. No open ports, no login page, no clues.

• Change firewall rules
• Redirect traffic
• Install malicious configurations
• Lock you out entirely

Even with strong passwords and HTTPS enabled, exposing the management interface to the internet is a risk. Port Knocking adds a stealth layer. The interface doesn’t even appear to exist until you authenticate

Here is a summary of the configuration steps for setting up Port Knocking on a Vigor router.

1. Prepare the Tools

Download and run the DrayTek Port Knocking Tool on your computer. You can also use Google Authenticator for generating TOTP codes.

2. Ensure Accurate System Time

Since TOTP relies on accurate time sync, it is essential that the router has the correct time. This can be checked and adjusted on the System Maintenance → Time and Date menu page in DrayOS 4 routers and on the System Maintenance / Device Settings / Time menu page in DrayOS 5 routers.

DrayOS 4	DrayOS 5

3. Enable Port Knocking

Enable Port Knocking for Local Services and choose which services require protection, such as:

1. 1. • HTTPS management
      • SSH
      • Telnet
      • Other local services

This setting is available in the “System Maintenance → Management” menu on DrayOS 4 routers and in the “System Maintenance > Management > Service Control” menu on DrayOS 5 routers.

DrayOS 4	DrayOS 5

In DrayOS 5 routers, you can add administrators in addition to the default admin account. To do this, go to the “IAM / Users & Groups” menu page to create an IAM user profile.

4. Configure the Knock Profile

• • • Set the first knock port
    • Scan the QR code using the Google Authenticator app installed on your phone, or copy the TOTP key.
    • Paste the TOTP key into the Port Knocking Tool

DrayOS 4	DrayOS 5

1. 1. • Generate a 6-digit validation code
      • Verify the code on the router

Once verified, the router saves the profile and activates Port Knocking.

5. Attempt Access

If you try to access the router’s management interface via WAN now, it will fail because the port is closed.

6. Perform the Knock

In the Port Knocking Tool:

1. 1. • Enter the router’s WAN IP or domain
      • Specify the public port and protocol
      • Click Knock Ports

The tool sends the correct knock sequence, and the router temporarily opens the management port for your IP address.

7. Access the Router

Click Status in the tool to open the router’s web interface. You’ll now see the login page, as you’ve successfully authenticated.

The access granted through Port Knocking is strictly temporary. The session remains valid for one hour, after which it expires, and you must perform the Port Knocking sequence again to regain entry.

• Invisible attack surface
• Protection against brute-force attempts
• Dynamic, time-based authentication
• Works with existing management workflows
• No need to permanently expose ports

For MSPs, remote administrators, and security-conscious businesses, Port Knocking is a simple but powerful upgrade.

If you manage networks remotely or simply want to harden your router against modern threats, enabling Port Knocking is one of the smartest steps you can take.

Protect Router’s Management Interface by Port Knocking

https://www.draytek.com/support/knowledge-base/11836#DrayOS5_section

This article includes configuration steps for both DrayOS 4 and DrayOS 5 routers