Wireless Network Troubleshooting

Here's the scenario:  high School with approximately 400 laptops.  Windows 2008 R2 handling DHCP, Meru WAPs.  We ghost the laptops with an image we use on all the laptops.

If you hand me a freshly ghosted laptop, I successfully login to the domain (scripts are processed, etc).  This would seem to indicate a successful connection to the network and a good IP addy.  Shortly after having a "working desktop (no more hourglass)", the spinning network icon shows up in the tray, and I am left with "Limited or No Connectivity" with the 169 IP addy.

rebooting the laptop, sometimes you connect successfully, other times, you get the No Connectivity thing.  We have two batches of laptops, some older ones run XP, the newer runs run Win 7.  this behavior shows up with both.  the randomness of success and failure is bizarre.

We have overlapping WAPs, if that is an issue, even though they all send out the same SSID.  So as you go down the hall WAP1 might have the strongest signal, but you can still pick up WAP2.  I would imagine WAP1 would answer your request for a connection.

The server is set to offer through for IP addresses, so this seems like I have plenty of IPs available.  Checking DHCP, I see 527 IPs have been handed out (IPhones and the like), so still plenty available.

I am at a bit of a loss here.  Where would you look next?
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Jakob DigranesConnect With a Mentor Senior ConsultantCommented:
ah --- missed that beat.

Install wireshark on Win2008R2 Server that's DHCP server
start a capture and try to connect one of your clients.

Then - if client doesn't get an IP - then look at Wireshark capture, and see if you can spot any DHCP packets from your client.

The DHCP process is as follows:

client sends DHCP DISCOVER (UDP68) to broadcast
Server responds with DHCP OFFER
client then reponds with DHCP REQUEST (asking for the IP Config offered)
Server responds with DHCP ACK stating that the client has that IP

If you see no packets of that kind, from YOUR client - then you should suspect that switches might block some traffic sent.
THen you must configure a mirror port on the switch, connect a PC with wireshark and do another capture to see if the DHCP DISCOVER packet reaches the switch at all
smckeown777Connect With a Mentor Commented:
Simple test to start...assign a laptop a static ip in the range rather than getting from DHCP...this will help to see if this is a DHCP thing or something else...

What you mean you have 'overlapping waps'? Are they on the same or different channel? Or you simply mean you have areas where you see signal from multiple waps? Long as they are on seperate channels you shouldn't be too bad...

Do the laptops work 100% on wired connection? Have you tested this? This will also eliminate things and if they DO work 100% on wired then we have a wireless issue...
Jakob DigranesSenior ConsultantCommented:
Since you since you hae Meru APs - you probably have Virtual Cells and APs overlap using the same channel - but that would give you no problems with IP-addresses, more likely performance issues.
But that' doesn't seem to be the case here.

First of all we need to know how clients are authenticated, as the assignment of IP-addresses varies among authentication method. 802.1X you get an IP after you've authenticated and authentication problems can give you problems with IP-addresses

Also - make sure your VLAN assignment is correct - what IP-Configuration do you have?
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dougp23Author Commented:

By overlapping WAPs, I mean we may have a 600 foot hallway and in that hallway, we have 3 or 4 WAPs to cover the area and all classrooms off to either side.  So it is quite likely that a notebook could pick up an SSID from more than one WAP.  All SSIDs are the same name.
Laptops work 100% of the time wired.

Occasionally, I do see a laptop when it is trying to connect, sort of stall at "Identifying".  I cannot remember where, but in Win XP there was a setting that if set wrong, a notebook could never connect.  I don't know where it is in Win 7 or even if it's there at all.

Our wireless signal is open and unencrypted if that helps.  There are no VLANs on the network.
Right, but have you channel seperation on each AP? So you have

AP1 - CH1
AP2 - CH6
AP3 - CH11
AP4 - CH1

I assume all WAP's are hardwired back to the main switch yes?

Normally when I connect a laptop to the network and the Network Identification screen pops up I always select WORK(not Home or Public) - this is the correct setting for your network and might make a difference...
Jakob DigranesSenior ConsultantCommented:
MERU doesn't use separate channels; http://www.merunetworks.com/products/system-director-os/virtual-cell/index.html

And even so - channel co-interference might degrade performance - not authentication.

Considering it is stuck on identifying, you're using 802.1X with IAS or NPS then?

Please confirm as this looks more like a authentication issue or possibly VLAN derivation issue
dougp23Author Commented:
I don't know where I would look to see if I am using 802.1x with IAS or NPS.

I agree that it looks like authentication issue.

smcke- not sure how the Merus work, but I think jakob has it right.  They "communicate" back to a central controller in the rack, so I think channels are less of an issue.  
All WAPs are hardwired back to a Cisco POE switch.
Cool, not familiar with Meru at all...

If you don't know where to look for 802.1x then you aren't using it would be my guess!!

Did you assign a static ip to the client - this will tell us if its a DHCP issue or an auth issue...simplest test
Jakob DigranesSenior ConsultantCommented:
Easiest way to see if 802.1X is configured

Look at how wireless settings are set on WinXP or Win7 PC
dougp23Author Commented:
Not using 802.1x.  Set to "no authentication".  

I am going to try the static IP tihng.
Jakob DigranesSenior ConsultantCommented:
Do your clients connect to a open network?

I think in Meru - if I remember correctly - it is something called Security profile which defines how you authenticate.

What do you do for clients to connect to the wireless network ?
Do you enter a password?
is the network unencrypted?
Already stated @jakob...

'Our wireless signal is open and unencrypted if that helps.  There are no VLANs on the network.'

So can't be auth related...not that I can think of anyways
dougp23Author Commented:
Thanks guys!  Turned out to be a little bit of everything (moving the WAPs just a bit here and there) and one switch was forwarding DHCP requests off to another subnet....

Thanks again!
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