About DHCP Reservations
DHCP reservation is a process in which a particular IP address is mapped with one computer that is typically a server that needs to have a same IP address permanently. When this is done, every time the target DHCP client computer requests an IP address from the DHCP server, the mapped IP address is assigned to it. Since the IP address is reserved for a particular computer while specifying DHCP reservation, it is not assigned to any other computer even if it is the only address available in the DHCP address pool.
Setting up DHCP Reservations
In order to set up DHCP reservations, administrators use physical address of the target DHCP client computer for which a particular IP address is to be reserved. Administrators can know the physical address of the target computer by either going to the computer physically, or by accessing it via Remote Desktop feature and using IPCONFIG /ALL command. ARP command can also be used to obtain the MAC address of the target computer using command line interface. Once the physical (MAC) address of the target computer is obtained, it is then specified in the DHCP Reservations option along with the desired IP address that is to be mapped with it.
Where DHCP Reservations Are Used?
In local area network, there might be times when administrators do not want to assign static IP addresses even to the servers in order to reduce administrative overhead. However, since the servers must always have a permanent IP address, administrators can use DHCP reservation to reserve a particular IP address for each server in the network. By doing so, administrators can eliminate the need of assigning static IP addresses to the servers manually, hence reducing the administrative overhead.
How DHCP Reservation Works?
Once an IP address is reserved for a computer and the computer is powered on, it broadcasts a DHCP Discover packet in the entire network. When the packet is received by the DHCP server, the server looks for and identifies the MAC address of the DHCP client computer (typically a dedicated server for some other service in the network). Once the physical address of the client computer is identified, the DHCP server looks in its reservation records and finds the IP address that is kept reserved for it and assigns the address to the DHCP client computer.
Set up DHCP Reservation for a Computer
To set up DHCP reservation in Windows Server 2008 R2 for a DHCP client computer in the network, administrators must follow the steps given as below:
- Go to the target DHCP client computer and fetch its physical address by typing IPCONFIG /ALL command in the command line interface and pressing Enter key.
- Log on to Windows Server 2008 R2 DHCP Server computer with domain admin or enterprise admin account credentials on which DHCP server role is installed.
- From the desktop screen click Start button.
- From the displayed menu, go to Administrative Tools > DHCP.
- On DHCP snap-in, from the console tree in the left pane, double-click to expand the DHCP server name.
- From the expanded list, go to IPv4 > <DHCP scope name>.
- From the displayed list, right-click Reservations.
- From the context menu that appears, click New Reservation.
- On New Reservation box, in the Reservation name field, specify a new reservation name.
- In the IP address field, type the IP address from the DHCP IP address pool that is to be reserved for the target DHCP client computer.
- In the MAC address field, specify the physical address of the target DHCP client computer that was retrieved earlier in step 1.
- Click Add to add the new reservation to the selected DHCP scope.
- Once added, click Close.
- Close DHCP snap-in when done.