DHCP Proxy vs DHCP Bridge mode in Cisco Wireless LAN Controller

The Wireless LAN Controller (WLC) supports two modes of DHCP operations in case an external DHCP server is used:

i) DHCP Proxy

--> 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 real DHCP Server IP address is not exposed in the air. 

--> The controller’s virtual IP address is normally used as the source IP address of all DHCP transactions to the client.

--> When multiple offers come 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.

--> DHCP proxy is enabled by default. All controllers that will communicate with each other must have the same DHCP proxy setting.

ii) DHCP Bridging

--> The DHCP bridging feature is designed to make the controller’s role in the DHCP transaction entirely transparent to the client. 

--> The real DHCP Server IP address is exposed in the air. 

-->  The real IP of the DHCP server is seen in the Offer and Ack packets instead of the controller’s virtual IP address.

--> By default DHCP bridging is disabled in Cisco Wireless LAN Controller, we can change the behavior by using the following command,

(Cisco Controller) >config dhcp proxy disable

(Cisco Controller) >show dhcp proxy

DHCP Proxy Behaviour: disabled