WLC DHCP for APs

Unanswered Question
Mar 4th, 2009

I currently use the internal DHCP server of our 4402 WLC. We also have a WiSM module as well. For the most part the internal DHCP server of the WLC works ok.

1. Is there anyway to setup option 43 in the WLC DHCP server? If possible I assume it would be from the CLI? No reference to this in the manuals.

2. I have noticed we see AP IP conflicts if we ever reboot the WLC that is running its internal DHCP server. It appears the internal DHCP server forgets IP assignments on reboot and will pass out an already in use IP address. Is this normal and if so for the DHCP server do all work that way?

I have setup a Windows 2008 DHCP server that I was going to phase in for AP DHCP assignments. I have the document to setup option 43 but it doesn't cover Windows 2008 server which looks to have different screens for this. I have been reading the Cisco document about setting up option 43 and trying to translate to Windows 2008 DHCP. I have Cisco 1131, 1142, and 1252s APs. Do they all use the same VCI?

I have been considering going to static IPs and just setup a small scope with only a couple addresses and use it to setup new APs out of the box then assign them and IP once that attach to a WLC.

Craig

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jeff.kish Wed, 03/04/2009 - 12:25

Hi Craig,

The internal DHCP server on the WLC cannot provide IP addresses to access points, so that might explain the problems you're having. It can only hand out addresses to clients, and if another server is handing addresses to the APs then there might be an overlap there.

Since it can't hand IP addresses to the APs, there's not much of a point in handing out Option 43.

Unfortunately, I can't help with the Windows 2008 configuration, as I have no experience with that product. Maybe someone else can jump in and give some info there.

Thanks,

Jeff

cef2lion2 Wed, 03/04/2009 - 12:32

Jeff

I do have the internal DHCP server handing out IP addresses to APs. The scope I have defined on the internal DHCP server is showing up on the APs. The only time I have issues with it is when the WLC running the internal DHCP is rebooted and I see duplicates for awhile till things settle down.

Craig

jeff.kish Wed, 03/04/2009 - 13:03

What version of code are you running? Maybe that's a new feature... Cisco's always been pretty clear that the internal DHCP server is only meant for clients. For every version of code I've used, it's simply not possible to use it for APs.

Are you sure you don't have an old or rogue DHCP server that's handing out the addresses?

cef2lion2 Wed, 03/04/2009 - 13:43

I'm using 4.2.176 code. I have used the internal DHCP for APs in prior releases. The scope I create is in the same subnet as the mangement interface of the WLC. On the mangement and ap-management inteface I point the DHCP setting to the address of the mangement interface. The APs are then picking up addresses from that scope. I'm positive I have no other rogue DHCP servers on that network.

Craig

Leo Laohoo Wed, 03/04/2009 - 14:41

I believe, please correct me if I'm wrong, that you can allow your AP to get IP Address from the WLC by configuring the AP-Manager interface into a different VLAN ID with the Management Interface and giving the AP-Manager the DHCP IP Address of the WLC.

Does this help (or make sense)?

cef2lion2 Thu, 03/05/2009 - 11:46

I'm moving away from using the internal DHCP for AP assignments anyway. Back to orginal post. I figured out the screens for Windows 2008 server DHCP and have option 43 setup but not tested.

Is option 43 just used for new or existing APs that do not have a primary WLC assignment?

If a Windows DHCP server is rebooted or restarted how does it handle existing leases? Does it remember them? Seems like the Cisco WLC internal DHCP did not.

Craig

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