You can use a client reservation to ensure that a DHCP client computer always receives the same IP address lease at startup. If you have more than one DHCP server that can be reached by a reserved client, add the reservation at each of your other DHCP servers. This practice allows the other DHCP servers to honor the client IP address reservation made for the reserved client. Although the DHCP server will act upon the client reservation when the reserved address is part of the available address pool, having the same reservation for the same client on multiple servers will not usually cause any problems.
If you are reserving an IP address for a new client, or an address that is different from its current one, you should verify that the address has not already been leased by the DHCP server. Reserving an IP address in a scope does not automatically force a client currently using that address to stop using it.
If the address is already in use, the client using the address must first release is by issuing a DHCP release message (DHCPRELEASE). To make this happen, at the command prompt of a client computer, type ipconfig /release.
Reserving an IP address at the DHCP server also does not force the new client for which the reservation is made to immediately move to that address. In this case, too, the client must first issue a DHCP request message (DHCPREQUEST). To make this happen, at the command prompt of a client computer, type ipconfig /renew.
For clients using Windows 95 or Windows 98, you can use the Winipcfg.exe program to cause release or renewal of the reserved IP address in DHCP. For clients using MS-DOS, and some clients using other operating systems, a computer must be restarted for the change to take effect.
Once these changes are made, the reserved client is leased the IP address now reserved for its permanent use each time it renews its lease with the DHCP server.
Reserved clients can have DHCP options configured specifically for their use. When options are configured for a reserved client, these values override any option type parameters distributed via server-based, scope-based, or class-based options assignment.
You can create reservations using any IP address in the scope's address range, even if the IP address is also within an exclusion range. Because of this design, when the 80/20 rule is implemented and all addresses in the scope are excluded (80% at one server, 20% at the other), reservations still function properly.
You can use this procedure to add a client reservation.
Membership in the Domain Admins group, or equivalent, is the minimum required to complete this procedure.
|To add a client reservation|
In the console tree, click Reservations.
On the Action menu, click New Reservation.
In New Reservation, type the information required to complete the client reservation.
To add the client reservation to the scope, click Add.
Repeat the previous two steps for any other client reservations you want to add, and then click Close.