The first priority is checking that the configuration for your D-Link range extender setup is correct; if your range extender keeps dropping the internet, position it so that the router provides a stable signal. Weak placement causes frequent disconnections.

Unplug the router and the extender for 30 seconds before turning them back on. Log in to the setup page using the default IP or web link to check for any firmware available for the extender. If there are any updates, download them to solve bugs causing the issue.

Interference from other appliances or devices should also be checked. If the condition still prevails, reset the extender to the factory set and reconfigure the D-link extender setup afresh. With these measures, one should be able to establish a stable internet connection!