I thought I understood DHCP

Discussion in 'Mac OS X Server, Xserve, and Networking' started by Jophster, Dec 8, 2013.

  1. Jophster macrumors member

    Jan 4, 2010
    Hi guys
    I seem to have a recurring problem in my household network.

    I have an ADSL Modem Router (changes depending on my frustration with current model!) but a common problem that seems to occur is that when I try to connect anything such as a MacBook to the network, it gives the computer the most random IP Address imaginable with a subnet mask of

    Any ideas as to why this may be happening?
  2. DeltaMac macrumors G3


    Jul 30, 2003
    Despite your concern about the actual IP address, are you able to connect and browse the internet?

    Are you trying to connect through wifi, or ethernet?

    If you power-cycle your DSL modem (turn OFF, or unplug the power cord, then on again), then try to connect with your MacBook, what appears as the IP address in the MacBook's Network pref pane?
  3. Jophster thread starter macrumors member

    Jan 4, 2010
    Unable to connect to the internet - can't even login to the gateway - the gateway IP is also a strange concoction!

    Connecting through WiFi.

    Rebooting can make it work - buts its just sporadic, it will sometimes just drop completely and then pick up again with this odd set of IP details.

    There is another router on the network but its relaying DHCP work to the other one in the house and is only really being used as a WiFi Access Point, don't think that should affect anything?
  4. dimme macrumors 65816

    Feb 14, 2007
    SF, CA
    If you have two routers connected to your modem and they are both serving DHCP addresses they need to be using different sets of P numbers
  5. chris.k macrumors member

    May 22, 2013
    If you get a 169.254 address it generally means your DHCP service isn't working properly. Those are "self assigned addresses" (mask /16) which the computer gives itself after a while if it cannot find the DHCP server.
  6. Consultant macrumors G5


    Jun 27, 2007
    Contact your internet service provider for support.

    I am guessing you only have a modem (with 1 ethernet port), not router. Some old modems are set to allow use by only one computer and you need to power cycle it to use with another device. Solution is to get an actual router such as the Apple AirPort Extreme or Express.

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