(Disclaimer:information below may not be in the order of your router or even possible as set ups are all a little different)
Linksys on old E-4200 i had.
Direct connect to computer or Laptop using Cat-cable
and login in. It usally is Admin user and Admin Password if router has been reset by holding reset button.
Set up wireless ID of Flexradio24 and Flexradio50 for 2.4 ghz and 5.0 ghz bands respectively with WPA-2 AES or personal
setup wireless password
Turn off UPNP
turn off wireless remote configuration
(((The last thing you do is below)))))))
Turn off Router DHCP Server (Not the dhcp it self)
Set router ip at 192.168.1.220 (Set IP OUT OF DHCP range of your main router with the last 3 digits )
SAVE and (((you are locked out at this point without doing full reset)) plug in to switch or router and go.
There is no remote configuration on router once it is put in this mode.
If not working go back do a hard reset and try again maybe some steps missed.
This sits outside on my deck. I can plug it in anytime and cover the whole back yard and then some.
I am not a network guru I worked hard at this by searching the internet over and found this information.
I failed at it a few times until I got to understanding.
The DCHP server is what got me locked out a few times on this router and had to hard reset and go at it again.
Hope this is useful to someone.