Sudden Connectivity Issues Could be Caused by a Cable Modem using IPv6

Whether accessing the Internet or other network resources, recent slowness issues may be caused by the cable modem if your Internet Service Provider (ISP) is Comcast.  If updates to devices or network equipment, those changes should be considered first as possible causes.  However, if changes have not been made or the issue affects multiple devices, the configuration of the Comcast cable modem might be the problem.  

Over the past few months Comcast has been updating the configurations on their business customers cable modems to roll out support for IPv6 addresses.  IP addresses are unique identifiers used to send and receive information on the Internet and internal networks so users receive the information they requested.  IP addresses are unique, like a postal address and zip code combination, allowing devices on different networks to communicate.

The current version of IP addressing is IPv4, an addressing scheme which has slowly run out of possible addresses to give because of the proliferation of devices on the Internet.  As a result, IPv6 was developed to create additional addresses.  Eventually IPv6 will be used by all devices but many devices are not configured to use it yet.  If the servers and switches on an internal network are not configured for IPv6, having it enabled in the cable modem can cause connectivity issues on the network.


To check the cable modem (different for each model)

1. Log into the cable modem
2. Click on LAN Settings
3. Scroll to verify the IPv6 settings are configured (this setting cannot be turned off)

If you find IPv6 is enabled on the cable modem, be sure to turn off IPv6 on network equipment and devices.  Network equipment includes firewalls, switches, wireless controllers, and access points.  Disabling the IPv6 Configuration for each of these devices is different based on manufacturer and software versions.

To disable IPv6 on servers and computer devices

1. Log into a network device.
2. Open "Control Panel" (If the options do not look like this, change the view to "Small Icons").





3. Open "Network and Sharing Center".
4. Click on "Change Adapter Settings".





5. Right-click on the network adapter providing Internet access and select "Properties".
6. Un-check the box next to "Internet Protocol Version 6 (TCP / IPv6)".





7. Click "OK" to save the changes.

Eventually IPv6 will be used by every device accessing the Internet and IPv4 will be rotated out.  However, until all network equipment and devices on a network have been properly configured to use it, having it enabled on your cable modem can cause sporadic and unpredictable slowness and connectivity issues.  Temporarily disabling IPv6 on network equipment and devices until your network is properly configured to use IPv6 should remove the slowness and connectivity issues.

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