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Linux, Netgear, 802.11, Pain

A few days ago, Debian Testing changed its Linux kernel from 2.6.38 to 2.6.39. My Wifi connection between Lenovo X201 and Lenovo T500 laptops and the Netgear DGN3500 suddenly stopped working. Oh it would start fine and the laptops would connect, then a short while later, or sooner if there was a steady heavy load, the Netgear would crash requiring a power cycle - even the HTTP server console froze. This never happened with 2.6.38.

I reported this problem to the Debian bugtracker only for the bug to be immediately closed as "So there's a bug in the router". I beg to differ that it is so certain. Anyway the triager has agreed that should the evidence become more than a single data point, then the bug would be reopened and a message sent upstream that there is a problem. Personally I think the iwlagn folk in the Linux development community really ought to be very interested in the problem that has suddenly started occurring.

I also reported the issue to the Netgear forum - I had forgotten how much I hate fora, email for me any day. Someone has also spotted someone having a similar problem with a different Netgear router, and a different distribution, but the same Linux 2.6.39.

I tried some experimentation varying the WiFi connection speed on the Netgear and varying the kernel version. I also tried Ubuntu Natty as well as Debian Testing, both the 2.6.38 kernel and 2.6.39 kernel - Natty only has a 2.6.38 kernel as far as I can tell.

  • The 2.6.38 kernel works fine with the router at "upto 270", "upto 130" , and "g only".
  • The 2.6.39 kernel fails to work after a period or with higher loads at "upto 270" and "upto 130", but works fine at "g only". The deduction from this is that something has changed in the 802.11n aspects of the 2.6.39 kernel that either:

  • has diverged from the standard as implemented in the router; or

  • has corrected a divergence from the standard, that is incompatible with the router. I am sure there are other possibilities, but these seem the most obvious.

I would have thought the Netgear folk would be investigating this now that two separate people have reported it independently on different Netgear devices. Also the Linux/iwlagn people really ought to be interested as to what change they made that is causing this problem to exhibit. We shall see.


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