Client connects but no IP address received through the AP

Unanswered Question
Jul 8th, 2008

I have a client that sees and attaches to a 1242 AP but is unable to get an IP address from the DHCP server via the AP. It returns a msg. saying Limited or No Connectivity on the client. Does anybody know what may be going on? Is this an AP issue or DHCP settings may have changed?

This is a WCS/LWAPP enviroment and more than one client is exhibiting the same problem.

Thanks!

I have this problem too.
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jeromehenry_2 Tue, 07/08/2008 - 09:55

Go to the controller, WLAN, click the WLAN (SSID) name this user tries to attach to.

On the WLAN General tab, you will see "interface". Write down the name of the interface used by this WLAN.

Now click Controller, and in the left, Interfaces.

Click the interface used by the WLAN. IN the interface page, you will see at the bottom DHCP server, that's the DHCP server to which you send the clients. Check if it's the right address and if the DHCP server works properly.

Most likely the DHCP server information is wrong.

Hope it helps

Jerome

Richard Atkin Tue, 07/08/2008 - 11:53

In addition to Jerome's suggestion, in some very rare cases, you may be using a DHCP Server that doesn't like the DHCP proxying mechanism used by the WLC (when DHCP does work, the client will see it's DHCP server as being the virtual interface on the WLC, usually 1.1.1.1).

You can disable DHCP Proxying on the WLC via the CLI, but this can bring its own issues in other situations.

Have you checked the WLC can ping the DHCP server?

If controller can ping DHCP Server, and if Jerome's answer doesn't resolve your issue, then I'll dig out the disable DHCP proxy CLI command.

The scope is enabled on the DHCP Server, right? ;o)

williamhayden Tue, 07/08/2008 - 13:22

I have recently disabled DHCP proxy to make my WLAN receive DHCP (good old fashion VLAN tagging). In the testing environment I didn't have this problem (all connected routes and no firewalls).

Now my controllers are in production but with a small number of access points until I can get this issue resolved. In production my controllers have routing protocols and FWSM to deal with.

I want to use DHCP proxy enabled but I am unsure at what addresses needed to pass through the firewall.

My question to you is what source address actually communicate with the dhcp server? Is it the management, a dynamic, or virtual interface of the controller that talks to the DHCP server?

Thanks,

Will

Richard Atkin Tue, 07/08/2008 - 13:31

Interesting one!

I've never specifically had to look at that, but logic would suggest that if broadcast forwarding is enabled, then the DHCP Lease Request will be broadcast out to the 'wired' VLAN, where the L3 interface of your router will pick it up and forward it onwards as dictated by the DHCP Helper Address?

So without having a packet sniffer to hand, my best guess is that traffic will come from the L3 interface on the router - but safest bet (unless somebody 'knows' the answer) is to get a packet sniffer on the case.

misramanish Tue, 07/08/2008 - 14:10

Thanks for all your responses, but this issue is tied to only this one AP. Other APs on the same SSID network have no problems, clients attach to them and get IP addresses without any problems. DHCP Server info has not changed, besides clients attaching to other APs are getting IP addresses.

Let me state that this AP was working very well until a few weeks ago, and no changes have happened since then, other than an occasional power cycling on it.

Scott Fella Tue, 07/08/2008 - 14:23

What happens if you move the ap to a different port just to see if the cabling has issues.

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