Airport "Double Nat" error??

Discussion in 'Mac Basics and Help' started by gotmarx, Jan 7, 2015.

  1. gotmarx macrumors newbie

    Jan 7, 2015
    I woke up this morning to find that I was not online. When I looked at my Airport it showed I had the green light for internet but the actual airport was blinking the yellow light and a message popped up saying that I needed to change airport base station from using DHCP and NAT to bridge mode. When I did that I lost the green light and the base station turned off. HELP PLEASE

    ps I am an idiot when it comes to making changes to my mac, I rarely if ever poke around in preferences....
  2. dburney macrumors member


    May 24, 2006
    Assuming everything was working fine beforehand… this is how I've overcome this pesky error.

    In my experience, this is caused by some snafu in my cable splitter. The splitter is used to split my coax connection between my cable box and my cable modem.

    I've replaced the splitter twice, and it is has fixed the issue. Last time, I simply disconnected all the cables from the splitter, reconnected and viola! Worked like a charm.

    Now this may not be your issue at all, but after beating my head against the wall the first time this happened out of the blue it's the first thing I check.

    Of course, I discovered the culprit was indeed the split signal by connecting my cable modem directly to the coax outlet on the wall. When that worked, I surmised it was the splitter. This was also after testing a variety of cables to make sure everything was working.

    Hopefully your problem is as simple as this.
  3. gotmarx thread starter macrumors newbie

    Jan 7, 2015
    Thanks, I will give it a try! I have been having other issues with the Airport over the last 6 months and I figure its "going down", of course it could have been from the last OS update. It worked fine until then...
  4. smithrh macrumors 68020


    Feb 28, 2009
    "Double NAT" isn't widely viewed as a real problem that needs addressing at all. Most people wonder why Apple even made this an error in the first place.

    Now, if the Airport is the ONLY router in your network and you're not connecting to another router with the Airport, then yes the Airport is in trouble, I've seen Airports go bad and need to be replaced, it does happen.

    Other than that, you should be able to ignore the double NAT notification.

    (I'd ignore the first reply to your post, double NAT has absolutely nothing to do with splitters.)
  5. rigormortis macrumors 68000


    Jun 11, 2009
    i lived in san Andreas for over a year. we had hughes net. i was forced to use double nat because the hughes modem wouldn't pass the ip address to the airport. to comment on your statement " "Double NAT" isn't widely viewed as a real problem that needs addressing at all. Most people wonder why Apple even made this an error in the first place"

    double nat actually can prevent apple from doing several things. downloading ispws, activating iTunes, and even restoring from internet recovery can fail when you are double nat,. i had this happen to me several times, and i had to drive 20 miles to the nearest public wifi hotspot, to even do basic things, like activate iTunes.

    the other comment about a cable splitter, is very dubious.

    a double nat is when for some reason your modem takes your real ip address say and translates it to passes it to the your wireless router which then changes it yet again to , this prevents incoming ports, ike file sharing or rdp and web services from working.

    and it also can prevent iTunes and apple tasks from working as well.

    i find it hard to believe a cable splitter suddenly made your cable modem not pass its ip address to your router.

    what probably happened was that your cable modem reset itself to the default settings, and you have to go to the cable modem and tell it to pass its routing / ip address to your airport
  6. Peace macrumors Core


    Apr 1, 2005
    Space--The ONLY Frontier
    Most cable modems get a dynamic IP from the NOC DHCP server.

    If the NOC DHCP server goes down the modem will default to 192.168.*

    The Airport router usually gets it's ip from the Cable Modem DHCP server.


    If the NOC DHCP server goes down you get the double NAT error.
  7. satcomer, Jan 11, 2015
    Last edited: Jan 18, 2015

    satcomer macrumors 603


    Feb 19, 2008
    The Finger Lakes Region
    The problem is most world ISPs are now offering a combination of a router and modem usually with much older wireless settings. Then traditional customers buy a more current wireless router. Then a problem of two NAT servers with DHCP servers creating network collisions. This is why Apple created the "Double NAT" errors.

    The general rule for home networks is to have just one NAT(DHCP) server in their home network, the router that is closet to the modem. All other routers after this should have NAT turned off, Apple calls this "Bridged Mode". This way you will not experience double NAT collisions, slowly down your TCP/UDP connections.

    So in the case where your ISP gave you their own moden/router combination then turn off wireless in that device. Then get your own modern wireless and turn off NAT (DHCP) in that new router but keep on the new wireless, Apple call this " Bridged Mode".
  8. aristobrat macrumors G5

    Oct 14, 2005
    In my case, the NOC DHCP server was fine, but there was a wiring issue that popped up on the outside of my house that stopped the cable modem from reaching the NOC. Same result.

    So in that regard, I don't think the advice about checking for splitters, etc, is dubious. I'd just expand it to generically say "make sure your cable modem is working fine before you go down the road of troubleshooting the router". I've seen both splitters and wires cause problems with installations that had been humming along fine for a long time.
  9. tbradnc, Mar 6, 2015
    Last edited: Mar 6, 2015

    tbradnc macrumors member

    Jan 17, 2013
    Right-o. It isn't really that complicated. If by choice or chance you can't (or don't want) to put your ISP provided modem/router into bridge mode just...

    1. Connect ISP router to ATC WAN port with an ethernet cable.
    2. Put ATC into bridge mode.
    3. Turn off wireless radio and SSID broadcast on ISP router.
    4. Setup a wireless network on the ATC.
    5. Connect any wired peripherals to the ATC, connect wireless devices to ATC wireless network you created in step 4.

    Now you have wired devices served by the ISP router - the ATC is just pretending to be a network hub for the wired devices.


    Your wireless devices are assigned IP addresses and get wifi from the ATC.

    This works fine. The only ethernet connection in our home is the Apple TV. Everything else is wireless.

    It's not a sin to use an ATC in bridge mode and let the ISP router handle the routing. But I prefer the wifi be provided by the ATC since 100% of our hardware are Apple products.

    NOTE: if you're doing all this over a wireless connection do step 3 last.. :)
  10. scubasme macrumors newbie

    May 8, 2009

    Actually taking the splitter out worked for me. Woke up with this problem today and I found this thread took out my splitter and now it works perfectly. Just wanted to share incase someone read your comment and was steered away from what was actually a solution.

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