Recipe14.11.Creating a Reservation

Recipe 14.11. Creating a Reservation

Problem

You want to create a lease reservation for a computer so that it always receives the same IP address.

Solution

Using a graphical user interface

1. Open the DHCP snap-in.

2. In the left pane, right-click on DHCP and select Add Server.

3. Type in the name of the DHCP Server you want to target and click OK.

4. Expand the target scope.

5. Right-click on Reservations and select New Reservation.

6. Enter the name, IP address, MAC address, and description for the reservation.

7. Click Add.

8. The reservation will now show up under Address Leases and will be marked as inactive until the target client requests a lease.

Using a command-line interface

The following is the general syntax for adding a reservation:

> netsh dhcp server scope <ScopeID> add reservedip <ReservedIP> <MAC_Address> <ClientName> <ClientComment>

The following command creates a reservation for IP address 10.1.2.5:

> netsh dhcp server scope 10.1.2.0 add reservedip 10.1.2.5 000102C8B474 rallen-wxp "Robbie's laptop"

Using VBScript

See the Introduction for more information on how to run the netsh command from within a script.

Discussion

In some situations, it is not ideal to let hosts obtain an IP address dynamically. For example, web servers need to be referable by a friendly hostname (e.g., www.rallencorp.com), which is associated with an IP address. If that IP address changes, the DNS record for the hostname also needs to change. The propagation delay while the record is updated could result in some clients getting errors when trying to access the web site. The solution for this, and any other server with DNS dependency, is to create a reservation.

When you create a reservation, you associate a MAC address with an IP address. You can get the MAC address for a specific network adapter by running ipconfig /all and looking beside Physical Address. After you create the reservation, the next time that network adapter requests a lease, the DHCP Server will recognize the MAC address and assign it the IP address of the reservation.

You may be wondering that since you have to go to the trouble of creating a reservation for servers with static IP addresses, why use DHCP at all for these hosts. The primary benefit of still using DHCP is for the auto-configuration options and the ability to change settings such as DNS Server or WINS Servers across a large number of hosts. Using DHCP means you have to configure fewer things manually on the server. However, if you are provisioning network settings another way, perhaps via group policy, this might not be enough justification.