School wide wireless dropping.

[profit10]

Hi,

 

We are experiencing a problem with our wireless network at school. What happens is; a laptop will see the wireless network fine and connect but will randomly drop connection. This could be after 5 minutes or after an hour. The wireless is still showing as full signal but it just won't connect. Then it will just connect by itself again.

 

This is happening school wide and to any laptop at any time. All channels have been checked and changed where necessary so there are no conflicts. The wireless has been fine for years, nothing has changed and now this all of a sudden. We are really stuck.

 

If anyone has any ideas that would be great. Thanks.

[synaesthesia]

have you checked for IP conflicts, made sure there's ample space in your DHCP scope?

[Bradlys]

Another possibility could be your provider generally dipping. If you're on wireless machines they take a little longer to reconnect and this is noticable, where as hard-wired machines via ethernet have a quicker reconnect time.

[profit10]

I've had a look and can't see any conflicts. There is plenty of space in DHCP.

[Griff]

Whats the setup mate? number of APS controllers brand etc

[profit10]

They are Proxim AP-4000Ms and we have about 20 of them. I'm not sure of all the setup details as they were in place when I got here. I can look up any settings if need be?

[sted]

When you say any laptop are they all the saem so compaq 610's for instance (or all have the same wifi card) might be a windows update that requires does something odd requiring a newer version of the wifi driver. Might be worth reimaging one and not allowing it to get any updates see if thats any better just depends how easy it is to replicate

[profit10]

We have several different laptop types. They are XP and Win7, both experiencing this issue. Have tried reimaging, so it has done it before any updates and after.

[Griff]

Whats it like connecting with a mobile device phone or a tablet? you still getting the drop out?

[Dos_Box]

How many devices are connecting to the AP's at a time? Are there also ancillary devices in the classrooms such as teacher laptops, iPads, phones etc. that could be connecting as well?

[profit10]

There will be about 70 odd laptops scattered around the school. Other devices, phones etc would only connect if we gave access to them. There will only be a handful of these and not used often enough to see any issues really.

[Griff]

Man I hate wireless issues especially like you say works for years then boom... we had this last year I tore my hair out with it I don't even know how I fixed it but this is what I did you may of already tried all this

 

- shutdown all access points and rebooted them

- brought up just 1 access point to see if problem persisted

- gave machine static IP address to see if dropped out

- monitored wifi signal on phone to see if it was dropping on there

- check for any rogue aps in area of our APS

- went to the leisure centre next door to ask if they had installed any new wireless equipment lol

- changed APS to auto select channel, changed back to different channels

- hard reset the controller and rebuilt it

- changed the range the internal DHCP on the controll was kicking out

 

I think the hard reset on the controller and the changing DHCP range sorted the issue I litrally spent 2-3 weeks on the issue, we installed the wireless system ourselves so no one we could really turn to.

 

Best of luck with it

[Dos_Box]

Is the problem school wide or just confined to a specific area?

If it is school wide it may eliminate the AP's and put the emphasis on something at the backend.

Have you tried just running a ping -t from one of the laptops to a server to see whether it can still 'see' something even though the 'visible' network may not be available?

I also note those AP's are a, b, g. All of the laptops are set to use 'g' yes? It may possibly be that if one or more are set to 'b' only then it is killing the speed for the others when demand is high.

Edited October 14, 2013 by Dos_Box

[strawberry]

my first guess would be channel conflict. I know you've checked but humour me.... Which channels are you using?

[profit10]

They are on either channels 1, 6 or 11 as I was told these were best to use as they won't overlap. And it is set up so any APs nearby are on another channel. If nothing has changed though, why would this be the case?

 

Thanks for the suggestions guys, I will give them a go.

[noohad]

Check and see if there are any new firmware and update just one access point to see how it performs. Best of luck

[White_Fi]

I would first start with a spectrum analysis of the areas affected. looking for any patterns in time of day the issue occurs perhaps?

 

I would also get some sniffing going and to make it easier to analyse use Eye. P.A from metageek (believe it is still a 30day trial)

 

Dirty way to get a wifi card into monitor mode:

 

1)Get some flavour of debian (other disto;s are available ) running.

2)apt-get install aircrack-ng

3)airmon-ng start e.g airmon-ng start wlan0

4)airodump-ng mon0 -c -w

 

This will let you know form a protocol level what is going on.

 

Dos_Box is right about the .11b guys.

 

The worse part is the b client doesn't even need to associate to the WLAN. The AP just needs to hear it's probe request to enable the protection mode in its own beacon... Then the AP next to it hears the beacon from the original AP... It detects the non ERP client protection mode and enables the same flag... the ripple continues.

[neilmac]

Not true about 802.11b devices.

 

While the standard does allow for AP's to trigger protection on hearing an 802.11b probe request, manufacturers decided to do it on association.

 

An AP will announce protection in a beacon by setting the use protection bit to 1, and also use the Non-erp bit to signal if a non-erp station is associated. Only neighbouring APs invoke protection, the next in line don`t if the non-erp bit is set to 0

 

And this is for 802.11 b only devices.

 

NM