How to Open a Port With a Comcast Cable Modem

The type of networking equipment Comcast issues you depends upon various factors. While a basic Internet package will require only a standard DOCSIS cable modem, other services may require the use of a modem capable of network address translation. Comcast may assign both a router and a modem for this, or they may just provide you with a single gateway modem. In this case, you will run into occasions where you must open a port your programs use on your Comcast modem. Fortunately, all assigned gateway modems come with an onboard graphical user interface that allows you to open the port quite easily. Although the methods for this procedure on each device are similar, there are important differences when it comes to accessing the interface and making the necessary configurations. Before accessing the interface and opening the port for your particular brand or model, you must first obtain your internal Internet Protocol (IP) address.

Yellow network cable connecting to the internet slot
How to Open a Port With a Comcast Cable Modem
credit: korn_a/iStock/Getty Images

Obtain Internal IP

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Open the Run window by simultaneously holding the “Windows” and “R” keys.

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Type “Control NetConnections” in the Run window and press “Enter.” This will run a Network Connections window.

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Right-click your local connection’s icon and click “Status.” This will open a new dialog box.

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Click the “Details” button. This will open a second window containing connection statistics.

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Write down the address provided beside “IPv4 Address.” This is your local network address. Click the “Close” button to close Details and then click “Close” again to close Status.

Arris Cable \ Touchstone Telephony Gateways

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Start your Web browser. Any browser should work to access the interface on the Arris Cable or Touchstone telephony gateway modem.

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Erase your start page URL address from its address bar and then replace it with “192.168.2.1” and press “Enter.” This will load an Enter Network Password window.

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Type “1234” in the “Password” box and click the “OK” button. This will open the gateway modem option’s page.

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Click the “General Setup” button in the left pane. This will expand a list of setup-related options in the left pane.

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Click to expand the “NAT” menu and then click the “Virtual Server” link. This will provide a new set of options at the center of the screen.

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Select the “Enable Virtual Server” check box. Type your local IP in the “Private IP” field and then type the port you want to open in both the “Private” and “Public” port boxes. Click the “Type” drop-down and click to select the protocol type. If you're unsure of it, select the “Both” option.

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Type a comment for this port rule in the “Comment” field and then click the “Add” button.

D-Link Cable Modem Gateways

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Open your Web browser. Any browser should work well with the D-Link’s web-based interface.

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Clear the existing URL from the address bar, enter “192.168.0.1” and then press “Enter.” This will open a D-Link Log In page.

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Type “admin” and “password” in the “Username” and “Password” fields and click the “Login” button. The D-Link user interface will appear.

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Click the “Advanced” link at the top of the page. This will change the options that are available in the left pane.

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Click the “Forwarding” button. This will expand a Port Forwarding options table at the center of your screen.

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Type your local address in the “Local IP Address” field and then type the port you want to open in both the “Start” and “End” port fields. Click the “Protocol” expansion menu and select the protocol type. You may select the “Both” option if you are unsure.

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Click the “Enabled” check box and then click the “Apply” button.

Linksys WCG200 Comcast Cable Modem Gateway

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Start your Web browser. Most browsers should work fine with the WCG200 interface.

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Type “192.168.1.1” in its address bar and press “Enter.” This should open a Log In dialog. If you receive the Page Cannot Be Displayed error, try “192.168.0.1” and press “Enter.”

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Type “comcast” and “1234” in the “Username” and “Password” fields and click “Log In.” If you receive an invalid username or password error, type “admin” in the “Username” field and leave the "Password" field empty.

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Click the “Applications & Gaming” tab. This is fifth tab located near the top of the page. This will display a Port Range table at the center of the page.

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Type the name of the program to which the port belongs in the “Application” box. Type the port you want to open in both the “Start” and “End” boxes and then click to expand the “Protocol” menu. Click to choose “TCP,” “UDP” or “Both.” If you're unsure, select the “Both” option.

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Type your local address in the “IP Address” field and click the “Enabled” check box. Click the “Save Settings” button at the bottom and close the interface.

Motorola SBG-series Cable Modem Gateway

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Open your Web browser. While the SBG-x interface may not work with all browsers, it will function properly with Internet Explorer or Mozilla Firefox.

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Type “192.168.0.1” in the address bar and press “Enter.” If you receive an error, try “192.168.100.1” and press “Enter.” This will open a Motorola Log In web page.

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Type “admin” in the “Username” box and “motorola” in the “Password” box and then click the “Login” button.

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Select the “Advanced” link at the top and then click the “Forwarding” button. This will expand the Port Forwarding table at the center of your screen.

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Type your internal address in the “Local IP Adr” field. Type the port you want to open in the “Start” and “End” port fields. Expand the “Protocol” menu and select “TCP,” “UDP” or “Both.” Select “Both” if you are unsure.

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Click the “Enabled” check box on the right and then click the “Apply” button at the bottom.

Netgear CG814 Comcast Cable Modem

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Open a Web browser. Any browser should work well with the CG814 interface.

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Type “192.168.0.1” in the address bar and press “Enter.” This will prompt you for your log-in information.

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Type “comcast” and “1234” in the “User Name” and “Password” boxes and then click the “OK” button. This will take you to a Welcome to Comcast Home Networking page.

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Click the “Feature Setup” link, which is located at the top. This will display a new set of options at the center of the page.

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Click the “Port Configuration” link. This will expand a Port Forwarding section near the bottom of the page. Type the name of the application to which the port you want to open belongs in the “Application Name” field. Type the port number you want to open in both “Port Range” fields.

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Expand “Protocol” and select the type the port uses. If you're unsure, select “Both.” Type your computer’s IP address in the “IP Address” field. Click “Enable” and then click “Apply” to save.