Conflicting DHCP Range on Airport Extreme

Discussion in 'Mac Accessories' started by userjohn, Jan 17, 2015.

  1. userjohn macrumors member

    Mar 24, 2011
    I recently saw an error "Conflicting DHCP Range" on my Airport Extreme (newest model), via Airport Utility (on both Mac and iOS). The error usually, but not always, appeared in those apps, despite no apparent network changes. I didn't think to check whether the physical light on the router always matched the app's status. I never noticed actual network problems despite the error message. The Airport's WAN port is not connected to another router, and there should be no other DHCP servers on the network. I had another identical Airport Extreme wirelessly extending the network (but even after I disconnected it, the error remained).

    Can anyone please explain the possible reasons? If I connected a device with a static IP within the allowable DHCP range (even if no actual assignment or attempted assignment of that IP occurred), would that error occur?

    I connected devices that may have had static IP's within the DHCP range. However, even after changing the DHCP range to ensure it didn't contain those IP's, and even after disconnecting those devices entirely, I still saw the error. Does the error mean a problem occurred at any time in the past, or does it mean there is a "current" problem (e.g., since the last restart of the router)?

    I finally tried the option to "ignore" the error, which seemingly required clicking "Update" to restart the router, and the error went away. Did that merely "dismiss" that specific past "error report", or will the router now ignore all errors of this type from now on? It seems odd that merely dismissing an error report would restart the router! If future error reports will be suppressed, can I "unignore" the error (without resetting the router entirely)? Can I get any more information about the past error (such as the IP, or date/time)?
  2. userjohn thread starter macrumors member

    Mar 24, 2011
    To follow up on the above, I again see the error "Conflicting DHCP Range" in the Status box under the Summary tab in Airport Utility, but with a green dot next to it, and when I click on it, I see a pop-up menu with the first menu item "Ignore" that is checked. If uncheck "Ignore", the dot changes from green to amber.
  3. RMo macrumors 65816


    Aug 7, 2007
    Iowa, USA
    What kind of modem are you using from your ISP? If it's performing its own routing functions, you may need to reconfigure it as a simple bridge. (Most cable modems are already like this; most DSL modems are not. Or at least that's been my experience with the limited set of ISPs I've used.)
  4. userjohn thread starter macrumors member

    Mar 24, 2011
    Thanks for the suggestion. I don't have a modem. The Airport's WAN port connects to an Ethernet jack in the wall that supplies the Internet connection. There should be no routing functionality on that jack, but is there an easy way for me to confirm that?

    I've been using this network for a long time without this error. I recently changed the DHCP subnet from the default of 10.0 to 192.168, but I don't see why that should matter (and I don't recall the error happening immediately thereafter). Also I've recently experimented with extending this network wirelessly, and I wonder if that somehow caused this error.
  5. DeltaMac macrumors G3


    Jul 30, 2003
    Your "Ethernet jack in the wall" comes from somewhere - at least a switch, maybe a modem.
    You may discover that the IP address that is fed through that line may conflict with the 192.168 address that you are now using. (A static IP address in that same range may be the whole problem.)
    You probably have no control over the external address, but you can certainly change your own DHCP range. I wonder if it also could be one of your devices that connect wirelessly - although you would usually get a "device is already using address 192......." or something like that.

    So, you could change your own range back to 10.x.x.x

    What device are you using to extend your network?
    Check that your attempt to extend your network didn't also introduce another router also providing DHCP.
  6. userjohn thread starter macrumors member

    Mar 24, 2011
    Thanks, I realize of course there's equipment on the other end (should be a switch), but as I said, I don't think there should be routing functionality on that jack. The WAN address I see on the Airport is a completely different publicly routable IP address.

    So far, I've only seen my devices on my subnet, and I've not seen errors on any of them about an IP being in use already. I can try changing back to 10.0.x.x, but if the error is specific to 192.168.x.x, I'd like to understand why, if possible. Is there an easy way for me to confirm for sure whether any external device is causing this error?

    The network is being extended now using another Airport Extreme (identical model, except refurbished), which was configured "automatically" by Airport Utility to extend the existing wireless network. I also previously tried extending using a Netgear extender (model EX6200), and tried a wireless bridge over two Ubiquiti Nanostation Loco M2's (I'm about to post about those experiments also), but those devices are no longer connected.
  7. DeltaMac macrumors G3


    Jul 30, 2003
    Large network, small network, full-time sys admin or tech office?
    or small business, or apartment building with a central ISP connection, or your own home?
    Just guessing here - but if you know about every device that is connected to your network, and you also know that no other device is connected to the same 192.168.x.x range that you want to use (don't know if that could possibly interfere, could be a mis-managed switch, etc )
    Maybe you can check the network setup in each owned device. The logs in your router might give you some help, too.
    Maybe you are just unlucky enough to change to a DHCP range that is managed in your WAN, and the switch, etc has some partial block - maybe (badly) assigned static IP's within that range. The more I think about that, there's more possibilities.

    I think you should know that I am talking past my knowledge - and also that you haven't said anything about your larger network, other than basic info - and maybe I don't want to know more about that. (and I keep talking :rolleyes: )

    My final though here, is - use what works. It would be nice to know why that IP range has problems, but I'm thinking that you might be going after some weird glitch in your network, and simply moving off to a working range will take that out of your daily thoughts. (maybe bring that to a sys admin's attention :D )

    enough rambling - good luck to you!
  8. eduardrw macrumors 6502

    May 20, 2013

    If you receive internet connectivity on this ethernet jack THERE IS A ROUTER INVOLVED.

    My suggestion is to connect the WAN port of your Airport to the "ethernet Jack with internet".

    Configure your Airport to provide DHCP and NAT. (you may receive a double NAT warning - ignore it)
    Configure your WIFI and connect the second Airport to extend WIFI.

    This allows you to have a firewall against other devices on the "ethernet jack with internet". (no IP address conflicts)
    And it will allow you to extend your WIFI.

    The other alternative is to configure the Airport as a bridge - however this does not allow for WIFI extension.
  9. userjohn thread starter macrumors member

    Mar 24, 2011
    Thanks for your further thoughts. I'm aware of every device on my subnet. I switched back to 10.0.x.x (after "unignoring" the error) and for now I don't see the error message. Perhaps it's a mismanaged switch as you suggested, which I may investigate later. I'll spare you further unnecessary details for now.

    I'd like to look at the router logs as you suggested, but I no longer know how, since Apple removed the option to view logs after Airport Utility 5.6. It seems 5.6 can still be run, with special effort, even on Yosemite to manage older Airport models (and access their logs), but I've seen comments that 5.6 won't properly manage the newest Airport Extreme (which also supposedly dropped SNMP support from the firmware).
  10. userjohn thread starter macrumors member

    Mar 24, 2011
    Thanks, but I'm not sure what you mean by "there is a router involved". I realize there are routers (aside from the Airport Extreme) eventually at the ISP (and beyond), and perhaps I'm not using the right terminology, but my point was that the jack connected to the WAN port on my Airport Extreme should not be exposing routing/DHCP/NAT services to the Airport Extreme, but merely a single public IP address. I don't understand how any other router out there should cause the DHCP error that I saw.

    The Airport Extreme is already configured to provide DHCP and NAT, and I've never seen a double NAT error (nor would I expect to, given the configuration above). The second Extreme was already set up to extend the existing network (and seems to work fine).

    The only "anomaly" was the "Conflicting DHCP Range" error (and even that didn't cause any functional problems that I noticed), which for now seems to be gone after switching back from 192.168.x.x to the default 10.0.x.x subnet.
  11. eduardrw macrumors 6502

    May 20, 2013
    Your "ethernet jack" most probably comes directly from a routing device (router/modem) with NAT/DHCP and a subnet. That's where your subnet conflict likely comes from.

    What IP address does your Airport get?
  12. userjohn thread starter macrumors member

    Mar 24, 2011
    Thanks for your input. I overlooked this message until just now. As I mentioned above, my Airport gets an externally routable IP address, and I see no evidence that the jack is connected to a device with NAT/DHCP or a subnet. As I said, reverting back to the default 10.0.x.x subnet removed the error. There may have been some misconfiguration or glitch involving the switch, as DeltaMac previously suggested as a possibility. I haven't had a chance to look into that further, but everything seems fine for now.
  13. Natzoo macrumors 65816


    Sep 16, 2014
    Not sure where i am
    What internet service provider because something is feeding that

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