Overview
This document covers how to modify/add/delete DHCP reservations. DHCP reservations allow for devices to be statically assigned an IP address without having to configure the device directly. Once it is set for DHCP, we can manipulate DHCP reservations to change its "assigned" IP. This allows us to document the device and its relative IP address. If the device is moved to another building, we can create a new reservation for it in the new DHCP scope. Microsoft IPAM does make it easy to manipulate DHCP reservations.
Prerequisites
- IPAM client installed on your workstation (see KB article to install)
- You have been granted a minimum of IPAM DHCP Reservations Administrator Role on IPAM.NIC.EDU
Procedures
Modifying an existing DHCP reservation
- Click on the DHCP Scopes menu item
- Select Reservations as the Current View
- Enter the last four characters of the MAC address in the search bar. IPAM does not use any delimiters in the MAC address
- Right click the DHCP reservation and select Edit DHCP Reservation...
- Now you can edit the MAC address (Client ID), Name, and/or description of the reservation. Note that the IP cannot be change - the reservation must be deleted if you want to change the IP address associated with the MAC address. However, if you are swapping out a device that will assume the same IP address as the old device, update the Reservation with the MAC address of the new device. Click on Apply
- Deleting a Reservation is simply selecting Delete instead of Edit DHCP Reservation...
Adding a new Reservation
- Click on IP Address inventory
- On the right side of the console, click on Tasks/Add IP Address
- There are ten (10) fields that you will populate/update in the Add IPv4 Address dialog box
- IP Address: Self explanatory
- MAC Address: Enter the MAC address of the device here.
- Managed By Sevice: Select MS DHCP
- Service Instance: If you are creating reservations for devices on the CDA Campus, select dhcp.nic.edu
- Device Type: Leave as Host
- Address state: In Use
- Assignment type: Reserved
- Client ID: The MAC address of the device without delimiters, click on Association MAC to Client ID
- Reservation server name: again, if on the CDA campus - dhcp.nic.edu
- Reservation name: Hostname of the device. Try to come up with a standard naming convention if there are going to be many devices of this type on the network. Note that the hostname will change dynamically when the device requests the reserved DHCP address.
Based on the IP address, IPAM will automatically determine what DHCP scope this reservation will be created in
- Reservation Description: If there is a certain device type, try to keep the description standardized. This will help in searching for a certain device type.
- Once you are done, Click on Apply or OK
Errors
IPAM/MS DHCP does not allow you to create multiple reservations with the same MAC address. If you do, you might see an error message like the following:
Here, the IP address was successfully added to the IPAM database, but IPAM could NOT create the DHCP reservation. I was trying to create a reservation for 0005A6059861 when this message occurred. If I go back and do a search for the MAC address in the IP Address Inventory, I can see that there is already a reservation with this MAC address
If this is the case, you will have to edit the existing reservation or delete the existing IP
Deleting an IP Address
From Adding an IP address in IPAM, you can see that an IP address can have multiple components. In the scope of this document, we have the additional component of a DHCP reservation. Other IP address could also have a DNS component if they require a static DNS record.
When deleting an IP address, you will be prompted whether or not you want the DNS and/or DHCP component deleted as well.
However, if a DHCP reservation does NOT exist, you might get an error similar to the following:
If that is the case, uncheck the Delete DHCP reservation box and try deleting the record again.