Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

Clients don't get IP from External DHCP


I have 2 controllers 4404 running (37 and 31 APs 1142 connected) .  2 WLANs configured and mapped with IP Helper to external windows 2008 R2 DHCP server on 2 Scopes.



Interfaces as follows


The few clients get connected to the SSID but keep waiting to get a IP address from the external DHCP server (windows 2008 R2- Lease time 8 days).

The option Controller - Advanced - DHCP option - Enable DHCP Proxy is ON and option 82 is set to AP-ETHMAC with timeout of 120 sec.

When the controllers are rebooted, Clients connect and get IP and this works for sometime but problem re-appears in 24 hours.

I have tried to disable DHCP Proxy option but it causes a lot of ARP errors with duplicate IP address and clients drop every 30 mins.

Please advice how to fix this problem.

Thanks in advance

Gokul Krishnan

Everyone's tags (3)
Cisco Employee

Clients don't get IP from External DHCP

first of all when you have dhcp proxy enabled , there is no need to put ip helper because the dynamic interface itself works as relay agent. So what you really need to do is to configure the primary dhcp server ip on the dynamic interfaces and see how it goes.

You can collect :

debug client < mac address >

while the issue is happenning


please make sure to rate correct answers

New Member

Clients don't get IP from External DHCP

Thanks for your reply. The primary dhcp server is set on the dynamic interfaces staff and student as the windows dhcp server. the iphelper address is configured on the 4503 switch for the wired clients. As I said the controller works as normal after a reboot but fail after some time. Do you know if there could be a fix for released for

I will post the debug message when the issue arises again. at present the clients are getting ip as I restarted the wlc.