How do i set up and configure an airport extreme with an ethernet cable connected to a dlink 868l (as the primary router) to create a single wireless network

There are at least 10 different models of the AirPort Extreme, and the tips and tricks differ according to which model that you might have.

You did not indicate what model that you have. Can we get the model number from the bottom of the AirPort Extreme? It starts with an "A" followed by four numbers.

Next, you did not indicate what device that you would be using to set up the AirPort Extreme, so we don't know whether you have a Mac, a PC, or whether you will be using an iPhone or iPad to set up the AirPort.

If you have a Mac, we need to know what operating system it is running. If you do not know, click the Apple icon in the upper left corner of he screen, then click About This Mac. Post back with the OS X Version number that you see there.

Finally, we need to make sure that you understand that the AirPort Extreme must remain connected to the D-Link modem/router using the Ethernet cable at all times. It cannot be disconnected.

Thanks for the additional information.

Power up the Extreme for a minute or two

Hold in the reset button on the back of the Extreme for 8-10 seconds and release

Allow a full minute for the Extreme to restart to a slow, blinking amber light

Power off the Extreme

Connect an Ethernet cable from one of the LAN <--> ports on the D-Link router to the WAN "O" port on the AirPort Extreme

Power up the AirPort Extreme for a minute or two

Click the WiFi icon at the top of your Mac's screen and look for a listing of New AirPort Base Station

Click on AirPort Extreme

That will get the setup "wizard" going. It will take a minute to analyze the setup and then present a window that looks similar to this, except that you will see a picture of the AirPort Extreme

Network Name.......Type in the exact same name of the wireless network that the D-Link router is using

Base Station..........Type in a name that you want to call the Extreme

Password...............Type in the password for the D-Link wireless network

Verify......................Verify the password

Click Next, and wait a minute while the wizard sets things up. When you see the message of Setup Complete, click Done

You are done