Posted by arlene

Some computers or other networked devices, such as routers or printers, might need to keep the same IP address all the time. For example, Microsoft very strongly suggests you be sure that your DHCP server has a static, unchanging address. There are two ways you can be sure a particular computer or device keeps the same static address. The first method is to manually configure the client using the client’s software. For example, when you configure a Microsoft Windows 2000 Professional client or a Windows XP client, you can specify a static IP address (along with other network information) using the TCP/IP properties page for the client.

If you use the first method, you’ll need to exclude the address you use from the address pool that you assign to a scope. If you forget this step and the address does fall within the range of a scope, eventually it will be issued to a client, causing a duplicate address error on the LAN.

A reservation is similar to an exclusion but is used for computers or devices that do support DHCP but still require a constant, static address. You can enter a reservation for an address that falls within the address pool for a scope. The reservation is linked to the computer or device’s hardware address sothat when it boots and begins the process of obtaining configuration information via DHCP, it will always receive the same address.

Exclusions are created when you create the address pool as explained earlier in this chapter. To create a reservation, carry out these steps:

1. Bring up the DHCP MMC console by clicking Start, Programs, Administrative Tools, DHCP. Expand the tree in the left pane to get to the scope in which the reservation will be created.
2. Expand the scope and right-click Reservations.
3. From the menu that pops up, select New Reservation.
4. The New Reservation dialog box appears. Enter a descriptive name you want to use for this reservation.
5. Next, enter the IP address that falls within the scope but that is to be reserved.
6. Enter the hardware address of the computer for which this address will be reserved. For Windows NT/2000 clients, use the ip con f ig /all command at the command prompt to get this address. For routers or other computers, consult your documentation.
7. Select whether the reservation will be used for a BOOTP request, a DHCP request, or both.
8. Click OK to dismiss the dialog box. The reservation is complete. The address is handed out only to the device that uses the hardware address (also called the MAC address) you defined for the reservation.

Note in this example the reservation was made for a router. Other types of devices for which you might want to reserve addresses (or exclude if the computers are statically configured) are important servers that are mapped to specific addresses in your DNS system. Also, if you have non-Windows clients, such as Linux or Unix desktops or servers, you might want to reserve an address for them if they cannot use DHCP.

More Help'n Tips: address, address pool, address that falls, client, computer or device, computers, dhcp, enter, ip, ip address, reservation, scope, static.

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