[vox-tech] Nursing home wi-fi mystery

[Ryan Northrup]

On May 6, 2015 10:05 AM, "Rod Roark" <rod at sunsetsystems.com> wrote:
>
> Here's a puzzle for you experienced network administrators.
>
> My mom-in-law is in a nursing home and I wanted to set up a MagicJack
> for her to save some bucks on her phone bills.  The facility has Wi-Fi
> with unsecured guest access where you just have to accept the terms of
> use via a captive web portal.
>
> Long story short, I set up an old netbook computer for her with Linux
> Mint Debian Edition, and disabled Network Manager and configured wlan0
> in /etc/network/interfaces.  I also wrote a PHP script that runs every 5
> minutes via cron to automate the portal login when required. It also
> detects when Internet connectivity is lost and executes an ifdown and
> ifup of
> wlan0 in that case.
>
> The problem: Frequent wi-fi outages, evidenced by DNS lookup failure.
> Clues are:
>
> 1. They only happen during the day when lots of staff or visitors are
> around.  The exception is shortly before midnight every night, which I
> figure is by design.
>
> 2. They occur at random times, about 6 times per day.  Thus clearly not
> an intentional timeout.
>
> 3. They are cured by the ifdown/ifup cycle. If that doesn't happen then
> the connection stays lost. Doing it fixes the problem every time.  Thus
> it has nothing to do with maxing out bandwidth.
>
> 4. The netbook is always assigned the same IP address by DHCP.  Thus it
> can't be IP address conflict (DHCP server misconfiguration).
>
> 5. It appears there are multiple access points in the facility with the
> same SSID.
>
> The only possible causes I can come up with are:
>
> (a) Someone is rebooting access points when they think that might fix
> something. This seems somewhat unlikely because it's also happening on
> weekends when administrative staff are not around.
>
> (b) Access point malfunction under heavy use.
>
> Any other ideas?
>
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I wouldn't rule out IP address issues.  It's possible that the AP / DHCP
server / etc. is being slammed with too many DHCP leases, resulting in
address exhaustion for that particular subnet.  This is especially
prevalent when a small business tries to use a residential or SOHO product
to run their wifi without moving from the default 192.168.1.100-255 range
(which is the most common on SOHO and residential routers), but I've seen
it happen even at hospitals with high-end Cisco-everything networks.

-- Ryan S. Northrup
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