Airport Extreme - double NAT error message

With that new information, you have two options, neither really being ideal.

1) Use the option in AirPort Utility to ignore the Double NAT and the AirPort will run with a green light. Hopefully, things will be OK with a Double NAT on the network. If you call Apple Support, this is what they will recommend.

2) Use the option in AirPort Utility to turn off the routing functions of the AirPort Extreme so that it it will run in Bridge Mode. Kind of a Catch 22 though. Technically, this is the correct setting for the AriPort. The downside to this is that other users will be able to "see" your devices.....AirPorts, computers, etc....and you will likely be able to "see" theirs. They won't be able to access any of your products unless they have the device password and vice versa.

If it were me, I would try Option 1 first, since other users will not be able to "see" the devices on your network this way.

Double NAT is an indication that you have two devices both trying to act as routers on a network. One of them is likely the "modem" (although it is no doubt more than a simple modem) that your ISP has provided to you and the other would be the AirPort Extreme.

Although you can sometimes get away with a Double NAT on a simple home network, normally you only want only one device acting as a router for the network while other routers are set up in what is known as Bridge Mode.

To see if your "modem" is in fact a modem/router or gateway type of device, we would need the make and model number of that device to check and see exactly what you have.

Bob, first of all thanks for your great support on this forum. You have helped me several times in the past.

I'm having the same issue as nickbog: I am in an office where they supply "free internet." It enters my office via an ethernet plug. I have direct connected my computer to the plug and it works fine. I have also tried to hook my airport extreme to the connection and got a double NAT error. It seems to run fine with the error but I'd rather not proceed that way.

However, the other alternative as you mentioned is Bridge Mode but when I switch to it, the internet stops working. I tried factory resetting the AE but still no go. Of course I have no way to reset the router or whatever it is that is feeding the internet into my space.

Kind of puzzling.

Kind of puzzling.

Not really. It is pretty clear that whoever set up the office router did so to only allow one device per Ethernet office port to connect to the Internet. This is very common in commercial networks.

So, you can connect a computer and use up that one connection. Or, connect the AirPort Extreme and use up that one connection.

But if you try to run the AirPort Extreme in Bridge Mode, that would require the office router to provide multiple IP addresses for that connection....and it won't...... since it has been configured to only provide one.

If you can get a hold of the office IT guy and ask him to provide multiple IP addresses to the Ethernet port where the AirPort is connected.....and he agrees......then you will be able to run the AirPort in Bridge Mode.

By running Double NAT on the AirPort, you are able to have the AirPort run as a secondary router. When you do this, the AirPort will provide multiple different IP addresses to connected devices and let all those devices "share" the one single Internet connection that is allowed at the port where the AirPort Extreme connects to the office network.

Depending on the rules and regulations of your company, doing what you are doing may be a violation of policy. Up to you to check on that though.

Interesting. It's a relatively small building with small offices. I don't know whether they will allow the extra IP addresses, but I'll ask.

I have a friend down the hall who has a non-Apple router. I'll check with him on his set-up. I assume he uses more than one device, but not sure. Is this limitation a general networking issue, or an Apple issue? Would a non-Apple router solve anything?

I didn't have much time to mess with it today, but I did try to connect my phone to the Double NAT network and it wouldn't allow it. I will be in the office over the weekend and make sure I can connect multiple devices to the Double NAT, if that is the only way I can run the network.

Thanks again Bob for your clear explanation.

I have a friend down the hall who has a non-Apple router

And, he is likely running in Double NAT as well. Apple is one of the few routers that will even bother to notify you of the Double NAT situation. Most other routers just do what they do.....route.....and don't even bother to tell you about Double NAT at all. Some examples.....major players like Cisco, Linksys, Netgear, don't even display a Double NAT notice at all.

I run Double NAT all the time when I'm traveling with an AirPort Express or AirPort Extreme. I connect the AirPort to the Ethernet port in the hotel room and set up my own private network in the room for multiple devices. The hotel router only "sees" one device this way......the AirPort router....so I only pay for one connection while my iPhone, iPad, Mac laptop can all connect to the Internet.

Thanks Bob. Today, I fully tested my "Double NAT" network in my office and as you said, all my peripheral devices are working fine and the network speed and reliability also seems fine. So, I'll just operate with a Double NAT until someone arrests me.