[PLUG] Can a faulty wifi driver affect router's behavior?

Arun Khan knura9 at gmail.com
Tue Dec 6 22:08:41 PST 2011

On Sun, Dec 4, 2011 at 4:39 PM, Mayuresh <mayuresh at acm.org> wrote:

> 1. The desktop/laptop dropping the connection (with no apparent trigger,
> except perhaps multiple sessions demanding data over network
> simultaneously), in which case you must manually do ifdown and ifup again.
> It won't re-connect automatically.

You have not mentioned brand/model of your WiFi AP; whether you have
flashed a 3rd party FW etc.

Also, are you using NetManager to manage the "network" connection on
your desktop?

I have a 6 yr old Linksys WRT54G series router which started behaving
similar to yours.  Power cycle would establish the network
connectivity but it would degenerate to nil over a period of time.
Signal strength on the applet display  > 80%.

Replaced the unit and the problem has gone away.

> 2. Desktop/laptop showing connection active with good signal quality, but
> router simply not responding to anything - even ping to it. In this case
> there was no option but to power restart the router and after it comes up
> again restart the interface.
> This was painful, though I had come to terms with it.
> Then NetBSD appeared out of blue on my laptop/desktop one fine day.

Wow, this is a candidate for the Guinness book :D

> The wifi driver on NetBSD for my hardware is so stable, it never dropped
> the connection over last few months of usage. Even if the router is
> switched off and on, the interface remains active and re-establishes
> connection automatically.

Good.  The real issue may be with the higher layer application
(NetworkManager) that is managing the network interfaces.     Looks
like NetBSD has a more stable Network Manager or whatever it is that
manages it's network connections.

> So far still nothing unusual. One implementation of driver can be better
> than the other.


> What surprises me is the issue no. 2 above, where I had to occasionally
> restart the router as it used to get hung has disappeared as well.

NetworkManager - suggest a bug report stating your scenario as a test case.

> Can a flaw in a wifi driver jam/hang a router?

A jammer is possible.   Mobile phone signals can be jammed.

> If that were the case, one
> can deliberately jam wifi drivers. One would expect routers to be more
> stable than that.

On the consumer oriented APs, which BTW are also used in many office
setups as well, do not expect much sophistication in this area.

A search for "wifi ap jammers" throws up quite a few links.  I found
this read very interesting

> Or is it just one off vulnerability with the router
> firmware, accidentally exposed by a bug in a driver. (Highly unlikely
> coincidence.)

Rule out nothing.  This is my observation - in most places during
testing phase, only "sunny" day scenarios are executed, there is not
much emphasis on "break" testing.    Most nasty bugs lurk waiting to
be discovered.

Thanks for sharing your experience, it does raise awareness re: WiFi security.

-- Arun Khan

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