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AP problem after adding Cisco WLC V7 to a network


Situation: After enabling the DHCP Proxy in Cisco WLC by following this instruction:

How to Enable or Disable DHCP Proxy in Cisco WLC V7, the client network wireless has some issues. The AP holds many client IP address forever and don't release.


Troubleshooting: Quoted from Cisco:

The DHCP proxy is not ideal for all network environments. The controller modifies and relays all DHCP transactions to provide helper function, and address certain security issues.

The controller’s virtual IP address is normally used as the source IP address of all DHCP transactions to the client. As a result, the real DHCP server IP address is not exposed in the air. This virtual IP is displayed in debug output for DHCP transactions on the controller. However, using virtual IP address can cause issues on certain types of clients.

DHCP proxy mode operation maintains the same behavior for both symmetric and asymmetric mobility protocols.

When multiple offers are coming from external DHCP servers, the DHCP proxy normally selects the first one that comes in and sets the IP address of the server in the client data structure. As a result, all following transactions go through the same DHCP server until a transaction fails after retries. At this point, the proxy selects a different DHCP server for the client.

DHCP proxy is enabled by default. All controllers that will communicate must have the same DHCP proxy setting.

If you use an external DHCP, you should disable the DHCP proxy. Otherwise, the AP will keep the IP address and that may cause the IP conflict. In below example, it shows 133 clients, but it doesn't have any wireless devices connecting to the AP. If you check teh bad address in DHCP, you will see some same IP address here.



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