Server 2008 DHCP does not hand out IP address to wireless divices


At one time we running RADIUS on our 2003 DC/DNS/DCHP server and everything worked fine.  We also have a few wireless access points that connect via WPA\TKIP and a password for guests.  Our network is one big network running on the same subnet.

When we upgraded to Server 2008(not R2) and used NPS things started acting weird on both type of access points, those using RADIUS and those just using a wireless password.  My workstation laptops connect to the wireless access points using RADIUS and Guests connect wirelessly using just a password.  The problem is if laptop is a new laptop or the laptop has not been here for an extended period of time it doesn't get an IP address on first connection.  I will get a local IP address of 192.168.x.x which we are not on.  I have manually go to the laptop and run ipconfig /release then /renew and it will get an IP address and then the laptop is works on wireless.  

This happens on both types of access points.  I've read where NPS settings needs to be set to give out an IP address via DCHP, but the problem I'm facing that I'm not only getting this problem with access points connecting via Radius, but also those that are just set up with a simple password like in a home wireless access point.  As i said it is all on the same subnet pointed to the same AD/DNS/DHCP server.   I don't understand why this problem is happening.  Laptops are running Windows 7 Pro or Enterprise. Any thoughts?
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It sounds as though the laptops are picking up IP addresses from a DHCP server on another network if they're getting the wrong addresses. Perhaps someone close by has just set one up. 192.168.x.x is the default network used by everyone and his dog.

Try temporarily disabling NPS and see if things return to normal. It may be that the WAPs need tweaking to pass the NPS traffic.
Patrick BogersDatacenter platform engineer LindowsCommented:

In NPS how did you configure Radius clients ?

Second, where is the 192.168.x.x coming from? It is not 'thought up' because it is a valid internal IP adress in stead of an APIPA adress which it should return when it doesnt know what IP to give you.
I would check the configs of the APs sounds like they may have DHCP helpers configured, is the new server's IP the same as the old server's ?  Also check and see if the AP's aren't configured to hand out dhcp from themselves
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Are your access points really access points or wireless routers?  
I've seen in plenty of businesses where someone thinks they are clever and use a wireless router as an AP and they forget to turn off DHCP on the router.  

You've definitely got another DHCP server on your network.
ozzalotAuthor Commented:
How can I found if there is another DHCP on the network?  I will check the access points, but I don't think they are routers.
If there is a DHCP server active on an adjacent WLAN and it's handing out addresses to anything in range, that suggests that it has no security enabled. Find out who owns that WLAN, and advise them that it would be a really good idea if they enabled WPA-PSK security on it at the very least; that would at least stop it being such a hussy...
Patrick BogersDatacenter platform engineer LindowsCommented:
Check the DHCP sections in the AP, it will show you.
Jeremy WeisingerSenior Network Consultant / EngineerCommented:
I agree that there seems to be a rouge DHCP server on the network. What I would do:

- Temporarily disable your DHCP server (stop the service)
- on a workstation, release and renew the IP address (this should receive an IP address from the rouge DHCP server)
- Start the DHCP service on your DHCP server (so that it will service as many clients as it can)
- on the workstation that has the IP address from the rouge DHCP server:
-- run ipconfig/all and get the IP address of the DHCP server
-- ping the rouge DHCP server
-- run arp -a and get the MAC address of the rouge DHCP server
-- attempt to connect to the rough DHCP server using http/s (this will give you a clue as to what the device is)
-- lookup the vendor information for the MAC address:
-- if you have managed switched, check the arp/mac tables to see which port the rouge DHCP server is connected to.

Following those steps should allow you to track down the rouge DHCP server.
Jeremy Weisinger meant a rogue DHCP server, not a rouge dhcp server !
You can very easily check if there is a rogue dhcp server, read this article:
Download and use the tool on a computer that preferably has a static IP address in your subnet. This can be run on the dhcp server itself for instance.

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Jeremy WeisingerSenior Network Consultant / EngineerCommented:
Oops! It was late, yes, I mean rogue. :) Thanks vivigatt.
ozzalotAuthor Commented:
Sorry I haven't responded to your posts.  I've been so busy here at work.  I plan on trying to find that rogue DHCP server today and will report back my results.  Hope you guys had a good weekend.
I've requested that this question be deleted for the following reason:

Not enough information to confirm an answer.
ozzalotAuthor Commented:
I'm sorry i didn't reply back.  I got flooded with work. I want to thank all you for your help. you were right there was a wireless switch setup with DHCP.
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