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DHCP Reservation Limitations in Windows 2008 R2

Friday, October 28, 2011

With Windows Server 2008 R2, you may encounter that you are unable to add a DHCP reservation if the reservation you are attempting to create is not within the address pool range.

For Example:

Scope192.168.1.0
Address Pool192.168.1.1 - 192.168.1.100
Subnet Mask255.255.255.0


Reservation: 192.168.1.101

Consider the following scearnio:

  1. You have a computer that is running Windows Server 2008 R2.
  2. Dynamic Host Configuration Protocol (DHCP) Server role is installed.
  3. There is an active scope on the DHCP server
  4. The distribution range does not cover all IP addresses in the scope.
  5. You try to add a reservation to the scope, but the reservation is outside the scope range.

The reservation for 192.168.1.101 may fail. The error message that will be displayed is: "The specified DHCP client is not a reserved client"

The Windows 2008 R2 DHCP Server will not allow reservations to fall outside of the configured address pool. To resolve this issue, expand the address pool to cover the entire subnet. If you do not want the DHCP server to assign addresses in a portion of the address pool, create an exclusion range. DHCP Reservations can be created even if they fall within an exclusion range.

The new scope for this example should look like this:


Scope192.168.1.0
Address Pool192.168.1.1 - 192.168.1.254
Exclusion Range192.168.101 - 192.168.1.254
Subnet Mask255.255.255.0

Reservation: 192.168.1.101

Alternatively, you could install a hotfix that is avaiable on the Microsoft website to correct this behavior.

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Recommended Books & Training Resources

MCITP Windows Server 2008 Enterprise Administrator: Training Kit 4-Pack: Exams 70-640 70-642 70-643 70-647 Windows Server 2008 R2 Unleashed