Wireless problems driving me mad

[jmak]

Our wireless system is playing up and I can't get to the bottom of it. We have hp procurve 420s all round the school - old but usually pretty solid. Recently network connection has been dropping out in the school hall - usually windows shows the wireless connection at full strength, but with no Internet connection. To me, this pointed towards a network issue between the AP and the DNS, but I haven't even been able to identify which AP is causing the problem. I have been using angry ip to check what I'm connected to, but when I've had connectivity problems I've sometimes seen dozens of results and sometimes seen none. I was expecting (hoping) to see one ip address in the results, thus identifying the AP.

 

When I run tracert to the DNS gateway, I don't see any intermediate steps. What tool should I use to try and track this down. I've looked at Wireshark, Netstress and Netsurveyor, but tbh I've got some learning to do and I'd be grateful for some hints on what direction I take before I dive in.

 

I'm also having a problem with a particular teacher's laptop. It connects perfectly in the staff room (where there is an AP), but not in her classroom. Same model of ap with same firmware and security. The curriculum laptops connect reliably in her classroom. All suggestions welcome (it's not preventing her from working, as there's a proper LAN point at her desk, but I would like to know why it's not working)

 

Thanks for listening

[maestromasada]

Every wireless setup is totally unique, a network within a network, therefore what I'm going to say make sense for me but it may be totally irrelevant for you; nevertheless I hope it will help you. What sort of wireless do you have ? WPA2 Enterprise? Are you using an IAS sever? if so it may be worth checking the authentication logs on the server. In regards to the wifi tool, have you use inssider? inSSIDer – Discover The Wi-Fi Around You | MetaGeek It will help you determine any possible channel collision that could degrade the signal. Particulry is you have home building or flats nearby, each one of the residents will probably have a wifi broadcasting at full strengh. I have seen cases where teachers laptop connect to these unsecure home users wireless

 

Good luck with this

Edited November 30, 2012 by maestromasada
grammar correction

[jmak]

What sort of wireless do you have ? WPA2 Enterprise? Are you using an IAS sever? if so it may be worth checking the authentication logs on the server. In regards to the wifi tool, have you use inssider?

 

Good luck with this

 

Thanks maestromasada. No IAS on our network. WPA2 enterprise wireless authenticated on WAPs. Completely forgot about inssider - used to have it on my 'droid phone, but haven't had it since that died.

[psydii]

Run continuous pings to your DC's and see if you spot any drops. Run inSSIDer on a separate machine simultaneously. Monitor what the RSSID and SNR being reported by the AP is.

 

Is the performance now reliably bad in the Hall, or does it come and go? Are there any radio mics on the 2.4Ghz band (unusual)?

 

If the laptop is reporting good signal strength, what is it reporting as its IP?

 

The teacher's laptop: does it have the latest set of RECOMMENDED updates from Microsoft? If yes, do the other laptops? If no, try them. Updates since September include many many changes to the Networking stack from kernel right up into the UI.

 

Is there any difference in driver version/settings between the teacher laptop and the others. How about BIOS versions?

 

I don't really have any answers, but hopefully investigating the above might make the root cause pop out at you!

[edutech4schools]

I had something like this and it turned out to be a DNS setting on 1 wireless AP pointing to an old server.

[psydii]

you can check which BSSID you are connected to by issuing the following command:

 

netsh wlan show interface

 

If you're lucky enough to have a macbook to hand you can use wireshark to capture the wifi management packets and run some analysis on them (such as retransmits vs data or RSSI over time etc)

[jmak]

Happily I'd left school by the time most of the replies came through.

 

Lots of great suggestions - for starters with inssider I quickly found that every surrounding building is broadcasting on channel 6!

 

And now you mention it, the standard location for teachers to place their laptops in the hall is on top of the AV trolley - which contains 4 radio mic base stations.

 

Plenty for me to look at on Monday. I'll also check out the windows version of Wireshark to see what more I can learn.

 

Thanks all.

[difinity]

Check the firmware on the APs. We had the same HP access points and improved reliability with a firmware update.

[tech_guy]

Have you changed the type of encryption used? We had an old wireless network with equipment from another well known manufacturer and the moment we changed the encryption used we had all sorts of intermittent connectivity problems which we traced back to the encryption and the wifi card used in all our laptops. Firmware updates (access points and wifi cards) did nothing so we ended up installing new access points across the site.

[psydii]

Unfortunately, Wireshark on Windows using a standard wireless nic is pretty close to useless for wireless troubleshooting. Windows wireless networking abstracts the wireless nature away, so nothing I am aware of can really see the 'raw packets'. That is why this beastie exisits: 802.11 Wireless Packet Capture Solution for Windows - AirPcap | Riverbed

 

That said, Wireshark on normal hardware can still capture the IP packets, so you can at least record evidence with timestamps on when things fail at layer 3.

Edited December 3, 2012 by psydii

[Duke5A]

We run a managed Cisco setup here. VLANs are actually tunneled to the access points by the controller. You set the location group the AP is in on the management console then it knows what VLAN to dish out. I've seen it where the AP will lose its config and it won't know what location it's in. I know these are two different setups, but it might be something to look at. It might explain why it'll associate, but doesn't go anywhere.

[jmak]

Thanks all.

 

I think I the WAP I'd installed in the Hall went rogue for some reason. Having removed that and moved everything away from channel 6 - which was being bombarded by non-school networks - things have settled down. I'm also going to try moving WAP's around within classrooms, varying transmit power and direction of antennae to try and further reduce interference. I don't think that was the fundamental problem, but a bit of time and effort will probably improve things further. Also all cabling was done 10 years ago, so that could probably do with some testing too.

 

For good measure, I've also provided a long network cable in the Hall too. What harm is one more cable to trip over????