In a simple DHCP scope, any device that connects and asks for an IP address is handed whatever IP is next available within the scope. If you have a device for which you always want to keep the same IP address, you could manually configure the NIC properties with a static IP address. Otherwise, a more centralized way to assign a particular IP to the same device on a long-term basis is to use a DHCP reservation. Using a reservation in DHCP to assign an IP to a device makes a lot of sense, because you can see that reservation right in the DHCP console and you don't have to worry about keeping track of the static IP addresses that you have configured out in the field. Let's walk through configuring a quick reservation so that you are familiar with this process.
We will be using a Windows Server 2016 machine as our DHCP server where we will create the DHCP reservation. Additionally, we will use our WEB1 server to be the recipient of this reservation by assigning WEB1 to IP address 10.0.0.85.
To create a DHCP reservation for a specific server or resource, perform these instructions:
- Open the DHCP manager tool.
- Expand the left-hand pane down into the DHCP scope that we created earlier. Under this scope, you will see a folder called
Reservations. Right-click onReservationsand click on New Reservation…. - Populate the fields. Your Reservation name field can contain anything descriptive. Fill out the IP address field with the IP address you want to reserve for this purpose. The last important piece of information is the MAC address field. This must be the MAC address of the device for which you want to receive this particular IP address. Since WEB1 is a Windows Server 2016 machine, we can get our MAC address by doing
ipconfig /allon WEB1.
- You can see Physical Address.........: 00-15-5D-AC-20-01 in Command Prompt—this is our MAC address for WEB1. Use it to finish populating the DHCP reservation.
- Click on Add and you will see your new reservation listed in the DHCP management console.
- Now make sure that the NIC on WEB1 is set to Obtain an IP address automatically. When WEB1 reaches out to DHCP to grab an IP address, it will now always receive
10.0.0.85because of the reservation, rather than getting whatever IP address is next available within the DHCP scope.
Typically, whenever a client computer is set to obtain an IP address automatically, it reaches out and looks for a DHCP server that hands to the client whatever IP address is free and next in the list. This causes DHCP clients to change their IP addresses on a regular basis. For desktop computers, this is usually fine. In many cases, however, it is beneficial to reserve particular IP addresses for specific devices, thereby ensuring they always receive the same IP address. Creating DHCP reservations is a good practice for servers, and also for many static devices on the network, such as print server boxes and telephony equipment.