I performed an upgrade of the firmware for the tp-link Archer C9 router. I got the firmware update from their website and then used the web interface, 192.168.0.1 and logged in. Installation of the firmware update seemed to go well, but then I lost connection after it rebooted.
Connect the router to your computer directly via one of the output ethernet connectors. You need to do this because at reboot, it gives a random number in the password for the router and you'll never get in wirelessly. Once there, you can again connect to the web interface. Change the password to the desired value and you should be able to connect wirelessly again. The directions don't explicitly tell you that the password you use will be lost.
