WLC 4402 and DHCP

Unanswered Question
Aug 13th, 2007

Having a issue getting DHCP working with clients. We have 1131 access points. They have assocaiated with the controller. Clients can connect but are not getting an IP address from the DHCP server. Not using internal DHCP in the WLC.

At our school the main networking group from a VPN for authenication. We place the AP and controller on the back side of the VPN. Security is open on the AP as the VPN handles that. We are given the IP address of the 2 DHCP servers. The DHCP server exist outside the VPN. The WLC and APs exists on the same private subnet. The DHCP servers exist on another subnet outside the VPN.

I have tested using the WLC DHCP and it works as long as the DHCP addresses are in the same subnet as the WLC and APs.

To have the WLC and 1131 APs work on this wireless nework we need to get the WLC to work with the external DHCP servers. I didn't know id this is a routing issue or if the DHCP servers do not support DHCP relay.

Craig

I have this problem too.
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frankzehrer Mon, 08/13/2007 - 20:47

Hi Craig,

did you configured the DHCP option 43?

This is a wide area of problems, but the main task is to understand the LWAPP and its mechanisms to configure everything properly.

Have a look for the deployment guide:

http://www.cisco.com/en/US/docs/wireless/technology/controller/deployment/guide/dep.html#wp1068287

Especially the Appendix C: How the Vendor-Specific DHCP Option (Option 43) is Used to Faclitate Controller Discovery

http://www.cisco.com/en/US/docs/wireless/technology/controller/deployment/guide/dep.html#wp1068287

The most wireless people struggled with this the first time touching the LWAPP.

;-)

Good luck,

Frank

cef2lion2 Tue, 08/14/2007 - 04:56

We are not having issues with the AP connecting to the controller. We are priming the APs with there IP address. DHCP option 43 is not an option for us as we have no control over the DHCP server. But that isn't a concern as the APs are connecting to the controller just fine.

Our issue is related to wireless client DHCP address assignement. We have configured the external DHCP server on the management interface. The external DHCP server is on another subnet then the APs.

Craig

remco.gussen Wed, 08/15/2007 - 22:29

Every VLAN that is configured on the WLC, can be assigned an ip address. This is an address that is responsible for the "dhcp relay". This address must be in the same subnet as the clients. The WLC forwards DHCP requests from the clients (via this VLAN address on WLC) to the DHCP server. The DHCP server can see the ip address of the WLC (from the correct VLAN) an returns an address from the correct pool.

I had the same problem an this solved it !

Gr.

Remco

dennischolmes Thu, 09/06/2007 - 16:56

Under your interfaces settings, add an interface on the vlan with the subnet of the dhcp scope you desire to use to handout client addresses. Make sure that the IP address for the interface you use is excluded from the scope. Make sure the vlan identifier is correct. Attach this interface to the physical port of the controller (same as the mgt interface) connection to the network. The controller will use the IP address of this interface to relay the dhcp requests. Also make sure to assign the SSID to this interface and not the management interface.

cef2lion2 Fri, 09/07/2007 - 07:17

I think this will work. I have tested the 4402 in a ifferent enviroment which I have more control over. DHCP is working and I did the same thing. I use internal DHCP in that case. Problem with the other enviroment is I have no control over the external DHCP server. I will have to ask about excluding the interface IP from the DHCP scope.

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