I have blocked in my router DHCP for all wired channels and even put the range for the one left, the wireless one, from .60 to .65 and put static IPs for the devices I want to allow to connect. Now theres a wired device that always gets an IP with .53 without DHCP being active. How is that possible? How can I block this unwanted device from getting an IP?

  • What is your router model and configuration?
    – Ron Maupin
    Sep 24 '16 at 5:34
  • Does the address of the unwanted device start with 169.254. ? If so, that's an APIPA address the device assigns to itself, usually a sign that DHCP DOESN'T work.
    – Mally
    Sep 24 '16 at 8:42
  • Nope, it's the good old 192.168
    – Bisonfan95
    Sep 24 '16 at 13:03

A few obvious possibilities:

  • the host has a statically configured IP address, thus not needing DHCP
  • the host has an old DHCP lease which is still being used
  • there is another DHCP server in your network providing the host with a DHCP lease

One thing to keep in mind: refusing DHCP requests from specific hosts does in no way block them from accessing the network.

  • Thank you for the response. In that case, how can I block him? When I access the mac filtering options in the router it shows me this: "MAC Filtering is only effective on ATM PVCs configured in Bridge mode."
    – Bisonfan95
    Sep 24 '16 at 13:06
  • That totally depends on the equipment you're using, but this is a feature not present in most low end equipment. The easiest way is to shut down all wired interfaces you're not using.
    – Teun Vink
    Sep 24 '16 at 18:21

Is this a Windows or linux box when yes, than the easiest and quickest way is to run wireshark on the device and filter the output to DHCP and there you can see that wo has assinged this IP to the device.

  • I know who it is, but I want him to stay the hell out of the network :(
    – Bisonfan95
    Sep 24 '16 at 13:04

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