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We just switched ISPs from AT&T DSL to Comcast. AT&T had its own (horrifically bad) router, but with Comcast we're using my 802.11n Airport Extreme. Unfortunately, the router randomly becomes unreachable. I'm still shown as "connected", but I can't ping the router anymore. This doesn't appear to happen when I've got WPA2 off, though I can't confirm for sure. Any idea why this might happen, or what I can do to prevent it? I would really prefer to be using WPA2 if at all possible.

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Do you have any wireless devices in range? A friend of mine had a similar situation, he never noticed that his internet only cut out when his cordless phone rang. The wireless signals were interfering.

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+1, good troubleshooting first step. i'd expect such interference to occur even with WPA2 off, but maybe non-WPA2 is more resilient. changing channels (or even frequencies, if all wifi devices support both 2.4 & 5GHz) might help. – quack quixote Oct 26 '09 at 7:48
This happens even late at night when everything is off. I've been running a continuous ping against the router and ping times vary wildly from sub 1ms to 25000ms. – Bob Aman Oct 26 '09 at 22:43
The router tends to cut out when ping times are on the really high end of the spectrum. I'm fairly sure the problem is just that the signal-to-noise ratio is getting really bad. This is expected. The problem is that it doesn't auto-reconnect after. I have to manually turn wireless off and reconnect. – Bob Aman Oct 26 '09 at 22:45
up vote 1 down vote accepted

It turned out that the router was on the other side of the kitchen wall behind the stove. Large metal objects completely wreck the signal-to-noise ratios. Moving the router so that it wasn't right next to the stove fixed the problem.

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