Clients associate, but don't get an IP address

Unanswered Question
Oct 16th, 2009

I need some help in determining if we are experiencing a bug or a configuration issue. Let me start by giving you details of how we are set up.

We have a WLC 4404 running at our corporate office. Our remote offices are running a 1242 AP in lightweight mode connecting to corporate via an MPLS T1. HREAP is configured so that local resources can be used. The APs are setup as trunks allowing only the VLANs required. The WLC hands out a static IP to the AP from the local native vlan. So, the AP has an IP in the same range as printers and local PCs at the site. Another VLAN is configured at the remote site for Wifi users. The local router (remote site) is providing the DHCP scope for the Wireless users. The remote site routers are mostly 2851s, but we also have 3725s. The 2851s are running 12.4(20)T, and the 3725s are 12.4(15)T7. We also have the sites configured 2 ways. Some sites have a router and 3560 switch, while most are 2851s with integrated switch modules. The problem we are experiencing is seen in all hardware configurations.

The issue is that if the WAN link is lost or if the router loses power and recovers, the local AP will reassociate with the WLC, get it's static IP and appear to function, but clients will associate with the AP, but fail to get an IP. They only get Not sure what is actually fixing the issue, but I have reset the AP from the WLC, reset the switch port, cleared the MAC tables and ARP, clear the DHCP bind and conflicts on the router/switch and rebuilt the DHCP pool for the wifi. Sometimes, I've removed the static IP option on the WLC and force the AP to get an IP from AD. This seems to kickstart the process. We have debugged dhcp during this and see no dhcp requests on the router when a client is trying to connect. After the above is completed, we sometimes need to disassociate the client and have them reconnect.

Anybody experience similar issues and find a resolution. As an attempt to resolve this, we moved the data VLAN that the PCs, printers and the AP connects to from VLAN 1 to a different VLAN, but leaving VLAN 1 active.

WLC -> MPLS cloud -> 2851 with vlan 50 for data, vlan 60 for voice and vlan 70 for wifi.

remote site dhcp:

ip dhcp pool VOICE

network (voice)

network secondary (wifi)

override default-router




option 150 ip

AP switch port:

interface FastEthernet1/22

switchport trunk native vlan 50

switchport trunk allowed vlan 1,50,70,1002-1005

switchport mode trunk

no logging event link-status

I have this problem too.
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weterry Fri, 10/16/2009 - 18:28

If you aren't seeing any dhcp requests, it sounds like the vlan mappings are getting messed up. But if that was happening, you'd have to re-configure the mappings to fix it.

If you are reconfiguring the vlan mappings, is there any chance you have two controllers? If so, make sure the wlan IDs are in the exact same order on both controllers. That is the most common reason for HREAP vlan mapping problems.

Other than that, I've got nothing. Packet capture is going to show if anything is leaving the AP at all...

smoyer Mon, 10/19/2009 - 05:17

We only have one WLC. It's odd that the problem only occurs after the AP goes into standalone mode then restores communication to the WLC. Everything appears to work as designed, but the wifi clients don't get an IP.

We just had it happen again, but this time, the fix was just shutting down the switch port forcing the AP to reboot. This fix doesn't always happen so smoothly as I mentioned before. Sometimes, it requires multiple changes to get the communications going correctly again.


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