Книга: Windows Server 2012 R2 Storage, Security, & Networking Pocket Consultant

Reserving DHCP addresses

Reserving DHCP addresses

DHCP provides several ways to assign permanent addresses to clients. One way is to use the Unlimited setting in the Scope dialog box to assign permanent addresses to all clients that use the scope. Another way is to reserve DHCP addresses on a per-client basis. When you reserve a DHCP address, the DHCP server always assigns the client the same IP address, and you can do so without sacrificing the centralized management features that make DHCP so attractive.

If the client is on the network and has a current IPv4 or IPv6 lease, you can create a reservation by completing the following steps:

1. In the DHCP console, expand the scope with which you want to work, and then select the Address Leases folder.

2. Press and hold or right-click the lease you want to work with. On the shortcut menu, tap or click Add To Reservation.

Otherwise, to manually reserve an IPv4 address for a client, follow these steps:

1. In the DHCP console, expand the scope with which you want to work, and then press and hold or right-click the Reservations folder. On the shortcut menu, tap or click New Reservation.

2. In the Reservation Name text box, enter a short but descriptive name for the reservation. This name is used only for identification purposes.

3. In the IP Address box, enter the IPv4 address you want to reserve for the client.

NOTE This IP address must be within the valid range of addresses for the currently selected scope.

4. The MAC Address box specifies the MAC address for the client computer’s NIC. You can obtain the MAC address by entering the command ipconfig /all at the command prompt on the client computer. The Physical Address entry shows the client’s MAC address. You must enter this value exactly for the address reservation to work.

5. Enter an optional comment in the Description text box.

6. By default, both DHCP and BOOTP clients are supported. This option is fine, and you need to change it only if you want to exclude a particular type of client.

7. Tap or click Add to create the address reservation. Repeat this step to add other address reservations.

8. Tap or click Close when you have finished.

To manually reserve an IPv6 address for a client, follow these steps:

1. In the DHCP console, expand the scope with which you want to work, and then press and hold or right-click the Reservations folder. On the shortcut menu, tap or click New Reservation.

2. In the Reservation text box, enter a short but descriptive name for the reservation. This information is used only for identification purposes.

3. In the IPv6 Address box, enter the IPv6 address you want to reserve for the client.

NOTE This IP address must be within the valid range of addresses for the currently selected scope.

4. The device unique identifier (DUID) box specifies the MAC address for the client computer’s NIC. You can obtain the MAC address by entering the command ipconfig /all at the command prompt on the client computer. The Physical Address entry shows the client’s MAC address. You must enter this value exactly for the address reservation to work.

5. The identity association identifier (IAID) sets a unique identifier prefix for the

client. Typically, this is a nine-digit value.

6. Enter an optional comment in the Description text box.

7. Tap or click Add to create the address reservation. Repeat this step to add other address reservations.

8. Tap or click Close when you have finished.

When you work with reserved addresses, you should take note of a couple caveats:

? Reserved addresses aren’t automatically reassigned. If the address is already in use, you need to release the address to ensure that the appropriate client can obtain it. You can force a client to release an address by terminating the client’s lease or by logging on to the client and entering the command ipconfig /release at an elevated command prompt.

? Clients don’t automatically switch to the reserved address. If the client is using a different IP address, you need to force the client to release the current lease and request a new one. You can do this by terminating the client’s lease or by logging on to the client and entering the command ipconfig /renew at an elevated command prompt.

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