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I have a strange limit where I can only have 5 devices connected to the internet at any given time. More than 5 devices can connect to the router, either through WIFI or ethernet, but only 5 can use the internet.

I've tried this on a Buffalo router, and now I have the Apple Airport Extreme. The different routers didn't matter.

Can the ISP somehow limit the number of devices connecting to the internet, even behind a NAT router? Is there a setting I need to change in the Airport Extreme to hide the presence of multiple devices?

My ISP is Nextera Communications according to

More details: The computers are actually connecting to the router. Just no outside internet. The devices are modern devices, such as iPhones, iPads, Macbooks, and Windows 7 PC's. This has been happening for a long time, and through multiple routers. The limit is definitely fixed at 5 devices.

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How are the devices connecting to the router? Is there any other device (such as another router) between the devices and the router that connects to your ISP? What device connects you to your ISP? (Perhaps they provided a combined modem/router and you added a router and have double NAT?) – David Schwartz Nov 8 '11 at 3:05
It's a condo. The internet is wireless beamed from the roof to a tower (according to their site). It's likely split out from a box on the roof out to the other 200 condos. I have one wired connection coming in, and the Airport Extreme connects directly to that. The devices connect directly to the Airport Extreme. A Windows 7 PC and an XBox are connected via ethernet. 2 iPhones, 2 laptops, and an Apple TV are connected via wifi. If 5 devices are on at one time, anything else that tries to connect to the internet fails. I can reset the router and connect any five devices again. – jwcooper Nov 8 '11 at 3:08
Do all the devices get assigned IP addresses? Do the five that work always have the same five addresses? It does sound like your connection supports five endpoints, period. Double-NAT for some devices may be your best solution. – David Schwartz Nov 8 '11 at 3:41
I think I figured it out. The router is setup in bridge mode, so the router on the roof is limiting the devices to 5. I can set it up as double-nat, and now they wont' be able to tell how many I have connected. How can I give you credit for this answer, as you led me in the right direction... – jwcooper Nov 8 '11 at 3:44

If your ISP is limiting you to five devices, double-NAT may be your best solution.

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Sounds like an old programmer joke. To solve any software development dilemma, just add another abstraction layer. . . – surfasb Nov 8 '11 at 9:51

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