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Configuring a DD-WRT Router for 3CX with QoS and Port Forwarding

In this article I will walk you through configuring your DD-WRT router to be used with 3CX phone server software.  I will show you how to forward the appropriate ports to enable phone calls to properly pass through your firewall.  I will also show you how to set up a QoS policy to prioritize your VOIP traffic over regular internet traffic.

Part 1: Configure Port Forwarding

First you will need to access your DD-WRT web interface (usually Once you login, you will need to go to NAT/QOS tab and then the Port Forwarding tab. Press the Add button twice and enter the following values (replacing with the IP of your 3CX server) and then press the Save button. The 3CX tunnel port is optional if you are not using it.

3CX DD-WRT Port Forwarding

Next you will need to add a port forwarding range for the 3CX RTP ports (9000-9049).  Go to the Port Range Forwarding tab and press the Add button and then enter the following values (replace with your 3CX server ip) then press Apply Settings.

3CX DD-WRT Port Forwarding (Port Range)


Part 2: QoS

You will need two things before configuring QoS on your router.  First you will need to determine your maximum upload/download speed.
Visit a website such as and run a speed test.  It will give you your speeds in Mbps which will need to be multiplied by 1024 to get your kbps speeds and then by 90% to get your max QoS speed.

So for mine, my calculations would be:

Download: 35.31 Mbps * 1024 * 0.9 = 32,541 kbps

Upload: 4.86 Mbps * 1024 * 0.9 = 4,479 kbps

Now that you know what your upload/download speeds are, you will need to get the MAC address of your 3CX server.  The easiest way to find this is to go to the Status tab in your dd-wrt router and then go to the LAN tab.  Find the IP/Host Name of your 3CX server and copy the associated MAC Address.  If you assigned your 3CX box with a static internal IP (recommended) then it will only show under the Active Clients section.


Now that you have your ISP speeds and your 3CX MAC address,  you will need to go to the QoS tab under NAT/QoS to configure your QoS settings.

Check the Enable radio button and then enter in your Uplink and Downlink values that you calculated earlier.  Then press the Save button.


Now under Mac Priority, enter in your 3CX MAC address that you obtained earlier.  Then press the Add button and select Premium in the priority drop down.  Now hit the Apply button and all of your QoS settings will be enabled.


If you have any questions, leave a comment below.

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