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I am currently using an Airport Extreme N Base Station (firmware version 7.6) connected to a cable modem to connect around 7 wireless clients and two wired clients to the internet. Prior to this I was using the same Airport Extreme with a DSL modem.

I don't know if my current situation arose when I switched to cable or if it started after a firmware update to version 7.4. My base station will lose access to the internet multiple times per day at random intervals. Attached is a screenshot of an airport status message that describes the Double Nat issue that seems to be causing my internet outages but I cannot understand why this is a sporadic problem rather than a persistent one.

I have googled for a solution and am not seeing any for my exact situation. I have read that this type of problem occurs when there is one router attached to a second and both are using NAT and DHCP. I understand that the way to fix this problem is to put either the modem or the Airport Base Station into bridge mode.

I would prefer to put the modem into bridge mode but it does not appear that my ISP, Cablevision, allows me to make configuration changes to my modem. I have tried putting my Base Station in Bridge Mode and have turned off DHCP and NAT but this results in a green status light on my Base Station with no access to the internet.

Is anyone familiar with my problem and what I need to do to correct it?

Airport Utility screen grab

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3 Answers 3

Reset to default
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Contact your upstream internet provider (Cablevision) and let them know you wish / need to manage the network and want their device to operate in bridge mode. Often someone will post the details on how to get into your modem and re-configure it in cases where the provider doesn't want to assist you, but I've always had good luck asking (especially the techs that will have to come to your location for trouble calls.) If you call once or twice and explain you call each time this Double NAT error happens, they will quickly realize what you need to run your network without having to call them on an ongoing basis.

The Airport hardware doesn't have anything to do with this detection, so the software in the router is detecting a change in the upstream network configuration and reporting it.

Usually I've seen this with metro-wide WiFi networks where a fault will change the routing through another router that is misconfigured or not normally serving the modems of customers directly.

Unless you're changing the settings of the Airport, the cause is almost surely up stream from the device itself.

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  • Thanks, it was really helpful to know that this Double Nat issue is not caused by a misconfiguration on my part. I spoke with Cablevision and they are unsure about why I am having this problem. The fact that the problem is sporadic makes it harder to fix. They are sending a tech Friday. We'll see if they can fix the issue.
    – somas1
    Jan 18, 2012 at 14:02
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If you've been using the newer version of AirPort Utility (version 6.0), try using the older 5.6 version instead (if it's not still on your system, you can download it from Apple's support site. It still work with the newer AEBS units, and it seems to have more granular control over your address sharing.

To make the configuration change, after selecting your base station, click "Manual Setup". Then click the Internet icon at the top of the window, then make sure the following are set as described:

Internet Connection tab -> Connection sharing: "Share a public IP address" TCP/IP tab -> Configure IPv4 using: "DHCP" (the rest should fill in automatically) NAT tab -- Make sure that "Enable default host at" is not checked; this will ensure NAT is not enabled on the AEBS

Click the Update button to apply the config change and restart the AEBS.

I ran into this exact same issue ever since I got my refurbished AEBS 802.11n dual-band unit a week ago, and today has been a really bad day for spontaneous drops. I just made these changes after futzing around for hours with the newer AirPort Utility app, and I believe this should fix the problem. I made the changes earlier today and so far everything is stable.

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I'm having the same problem as you with the same equipment. Cablevision Modem(Scientific Atlanta) -> Airport Extreme N and I get this issue sporadically but only when playing XBOX live or torrenting.

Perhaps our ISP is changing our VLAN to throttle traffic and the airport is seeing this packet shaping or other network changes (or actually reporting a true change to double NAT)

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  • 3
    Best to ask your question and link back here. Most people won't see an "answer" that's essentially me too
    – bmike ♦
    Mar 15, 2012 at 8:05

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