Switching from Cisco IOS DHCP to an external DHCP Server

My previous post about “Use a Cisco IOS Switch to Serve DHCP to Avaya Phones” was inspired by my need to quickly test connectivity with a remote site. The solution worked very well for us. Eventually we were able to deploy a server to handle all DHCP, and needed to switch over to the services on the box. My initial reaction was to simply use the “no service dhcp” command to disable DHCP, followed by adding an “ip helper-address” to the VLAN interfaces. Surprisingly the DHCP server never received any of the requests. After comparing configurations with another switch, I discovered I needed to re-run the “service dhcp” command. I had compared the “show proc | include DHCP” and noticed the DHCP processes missing on my new switch. Apparently the “ip helper-address” uses some of those DHCP services for analyzing and forwarding to the server. I ended up just removing all the “ip dhcp pool” statements to keep things clean and from causing any conflicts.

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