Re: new EX6400 extender
1. did you set it up via wps? if so its default configuration is running as a mesh network. That means it keeps the same ssid as your router. so it won't "appear" on your network list.
2. the client link device lights up if somethings connected to the extender. Is anything connecting to it?
3. if you didn't set it up via wps, did you set it up using the "onessid" feature? again, that'll keep the ssid the same as the routers