maybe the distance of the two routers a too far away to remain a stable wds connection.

You could try to set different SSID for your TL-WA855RE

we can't disable the 5GHz band for this dual band extender. "Don't want to use this channel" means do not configure this device to connect its 5GHz to a router.

by default, the ip address of 750RE is 192.168.0.1, if you set your computer's ip address to be 192.168.1.10, you may not able to access 750RE, you could try 192.168.0.10. However, the suggested way...

follow the quick setup instructions in the 850RE's box you will be able to connect it to netgear, after configuration, 850RE should have the same wireless password of your modem router, so it should...

you could reset the tplink device and reconfigure it, after reset, its default password is "admin"