Trouble getting IP from DHCP server when on Wifi
I have a weird issue with the majority of our laptop users when connecting through wifi on our domain network. They refuse to pick up an IP address. If they go over the LAN they pick up the IP address from the DHCP server no problem at all. The Access Points have a guest wifi network which has a different DHCP server and they pick up IP addresses fine from that every time. It is only when they try to get on the network over the corporate wireless network that they cannot get an IP address from the corporate DHCP servers. Same access points just a different SSID. The only difference I can think of between the corporate SSID and the guest SSID is that the corporate one has MAC filtering turned on. I have tried turning off MAC filtering but it does not seem to make any difference. I have tried IPCONFIG /renew and it does not seem to force it to pick up the IP address. Has anyone any suggestions as to what could be causing the problem on the Corporate SSID that prevents the laptops picking up an IP address? Thanks in advanceDarren
May 9th, 2012 10:04am

Are you sure that the corporate SSID is on a VLAN that has the relay agent configured correctly AND a DHCP scope that matches? Or do you have your corporate WiFi on the same subnet as your LAN clients?Guides and tutorials, visit ITGeared.com.
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May 9th, 2012 10:23am

The corporate wifi clients are on the same subnet as the LAN clients. Signal strength on the clients is excellent and like I said when they use the guest wifi that connects to a different subnet with a different DHCP server all works perfectly. If I set the IP address manually communications are normal (even on a cold start of the laptop). It is only if the wifi clients on the corporate SSID try to use DHCP that things fail.Darren
May 9th, 2012 10:31am

Ok, the single LAN simplifies the troubleshooting. Since you verified that manual IP configuration works, the network pipe is good. I would suggest that you run a packet capture on both sides of the access point to see what is actually happening with the DHCP packets. If they are making their way to the DHCP server, that is important info because if they are, what is the server doing with them and if not, what is happening at the access point.Guides and tutorials, visit ITGeared.com.
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May 9th, 2012 11:11am

OK got any good recommendations for a how to on packet capture. Both our DHCP servers are 2008 Server Core boxes so I'm guessing installing something like WireShark is out there. Darren
May 9th, 2012 11:34am

Darren Thorley wrote: The corporate wifi clients are on the same subnet as the LAN clients. Signal strength on the clients is excellent and like I said when they use the guest wifi that connects to a different subnet with a different DHCP server all works perfectly. If I set the IP address manually communications are normal (even on a cold start of the laptop). It is only if the wifi clients on the corporate SSID try to use DHCP that things fail. And how is the Access Point connected to your corporate LAN? Does it have an direct interface connected to the LAN(VLAN) - or is there any device in between the Access point and the DHCP server. I would advise to take packet traces of the DHCP traffic between client and server at the client side and at the server side, then you will quite easily discover, where the problem lies - but probably at the access point or some other device between the client and the server. For packet traces you can use Wireshark (www.wireshark.org) or on Windows devices the Microsoft Network Monitor 3.4 (http://www.microsoft.com/en-us/download/details.aspx?id=4865) . If your access point has it's own packet capturing solution, that would be probably the best place to start with. Wolfgang
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May 9th, 2012 11:35am

Darren Thorley wrote: The corporate wifi clients are on the same subnet as the LAN clients. Signal strength on the clients is excellent and like I said when they use the guest wifi that connects to a different subnet with a different DHCP server all works perfectly. If I set the IP address manually communications are normal (even on a cold start of the laptop). It is only if the wifi clients on the corporate SSID try to use DHCP that things fail. And how is the Access Point connected to your corporate LAN? Does it have an direct interface connected to the LAN(VLAN) - or is there any device in between the Access point and the DHCP server. I would advise to take packet traces of the DHCP traffic between client and server at the client side and at the server side, then you will quite easily discover, where the problem lies - but probably at the access point or some other device between the client and the server. For packet traces you can use Wireshark (www.wireshark.org) or on Windows devices the Microsoft Network Monitor 3.4 (http://www.microsoft.com/en-us/download/details.aspx?id=4865) . If your access point has it's own packet capturing solution, that would be probably the best place to start with. Wolfgang
May 9th, 2012 11:35am

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