How to Change the MTU Settings on a Comcast RCA Modem

You may need to manually adjust MTU settings on a Comcast modem.

When you sign up for Comcast high-speed Internet service, a technician will come to your home or office and install a cable modem. By default, all RCA modems used by Comcast technicians have a Maximum Transfer Unit size, also known as MTU, of 1,480 bytes. if you are experiencing problems with your Comcast Internet connection and have contacted Comcast for help, the support representative may ask you to manually change the MTU settings for your modem.

Things You'll Need

• PC running Windows XP or later
• RCA modem

Instructions

1. Make sure your Comcast RCA modem is powered on and properly connected to your PC with an Ethernet cable.

2. Open the Start menu and click on the "Run" button.

3. Type "regedit" into the text field and click "OK" to launch the Registry Editor tool.

4. Navigate to the HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Ndiswan\Parameters directory from the tree on the left side of the window.

5. Open the "Edit" menu at the top of the window, expand the "New" submenu and choose "Key."

6. Enter "Protocols" in the new text field and click "Enter."

7. Create another new key and name it "0" (the number zero).

8. Return to the "Edit" menu, expand the "New" submenu and select the "DWORD Value" option.

9. Enter "ProtocolType" in the text field and click "Enter."

10. Open the "Edit" menu, choose "Modify," enter "800" as the value and then click "OK."

11. Create another DWORD value and name it "PPPProtocolType." Then use the "Modify" menu command to set its value to "21."

12. Create a final DWORD value and name it "ProtocolMTU." Then go to the "Edit" menu and choose "Modify." Fill in the "Value" field with the MTU setting that Comcast has asked you to use. Click "OK" when you are done.

References

• Microsoft Support: How to Change the PPPoE MTU Size in Windows XP