@gerzs Are you using it as the main router or as access point to extend WiFi signal? There two operation modes (router and access point) and they are different in some aspects.

When you say it works fine with wire, what do you mean exactly? In other words, where are you connecting the wire to test it?

@mocelet I connected it to my laptop and did a speed test, it worked as expected.

I would like to use it as the main router.

@Kevin_Z 

"Connect your computer to the internet directly and verify whether you can access internet, if it works well, please connect it back to the Archer C6 by wired cable. "

Yes, I did this and after that I cannot access the web UI, I suppose due to there not being an internet conncetion according to the router.

@gerzs You don't need Internet connection to access the web UI (you mean the administration web of the router, right?). Try using WiFi, you should be able to open the web UI.

Is your laptop wired connection set with static IP address and DNS or it is dynamic / automatic?

Edit: If you're able to plug any wired device to "the internet" without the router, then you probably need to set the router as access point instead. Who provides you internet connectivity?

@mocelet @Kevin_Z 

Well, it seems like this was some weird Linux bug. On my ancient laptop with Win7, the setup went smoothly.