Dynamic Host Configuration Protocol (DHCP) is an invaluable service when you have a network larger than a handful of computers. It’s also a standard component of enterprise networks and subnetworks. Windows 2000’s built-in DHCP server allows Windows machines (and any other TCP/IP-based machines and devices) to obtain their IP addresses and network settings automatically, which can vastly simplify network configuration. In this article, we’ll discuss how to install and configure a DHCP server in Windows 2000, and we’ll explore some of the advanced features Win2K DHCP has to offer.
Create a plan
Before you configure your DHCP server, it is a good idea to have all your ducks in a row. Prepare and have all the necessary information up front before sitting down and configuring your server. For example, you may need to know:
- The scope of IP addresses that your server will manage (e.g., 192.168.1.50 to 192.168.1.200).
- Which machines require static IP addresses (i.e., those machines such as servers and routers that will not use DHCP to receive their IP addresses but will be set manually).
- Which network information you want to send out to DHCP clients when they get their IP addresses (e.g., the addresses for your default gateway, DNS servers, and WINS servers).
It is much easier to configure your DHCP server with this information at hand rather than scrambling for it at implementation time.
Installing DHCP on a Windows 2000 Server or Advanced Server is a fairly simple process. During the installation, you might get prompted to insert your Windows 2000 Server or Advanced Server CD (or locate the i386 folder on a local or network drive).
To install DHCP Service:
- Open the Control Panel and double-click Add/Remove Programs.
- Click Add/Remove Windows Components.
- Highlight Networking Services and click Details.
- Select Dynamic Host Configuration Protocol (DHCP) as shown in Figure A and click OK.
- Click Finish when prompted.
Configuring your DHCP server
After you install a DHCP server, go to Start | Programs | Administrative Tools | DHCP to open the Windows 2000 console for managing the DHCP service (see Figure B).
When setting up a DHCP server, the first thing you have to do is define a scope. A scope is a list of valid IP addresses you want the DHCP server to be able to assign to clients. When a machine requests TCP/IP information from the DHCP server, the information is provided from the scope you created.
Every DHCP server is required to have at least one scope. You can, however, create multiple scopes on a DHCP server to administer different subnets.
When you create a scope, you must select the range of IP addresses and you must specify the appropriate scope options to include. These options are what we were referring to above when we mentioned that you can assign other network information to your clients at the time they are given an IP address.
There are two types of scope options: Global and Scope. Global options are propagated to all the scopes that you create on that DHCP server, while Scope options are only for the individual scope that you are working with. For example, if you have different scopes for several different subnets and each subnet will have a different default gateway but will share the same DNS servers, you would want to set the DNS servers as a Global option while the default gateways would be set separately in each scope as a Scope option.
Table A shows a list of all of the Global and Scope options available in a Windows 2000 DHCP server.
|· Time Offset||· Trailer Encapsulation|
|· Router||· ARP Cache Timeout|
|· Time Server||· Ethernet Encapsulation|
|· Name Servers||· TCP Default Time-to-Live|
|· DNS Servers||· Keepalive Interval|
|· Log Servers||· Keepalive Garbage|
|· Cookie Servers||· NIS Domain Name|
|· LPR Servers||· NIS Servers|
|· Impress Servers||· NTP Servers|
|· Resource Location Servers||· Vendor Specific Info|
|· Host Name||· WINS/NBNS Servers|
|· Boot File Size||· NetBIOS Over TCP/IP NBDD|
|· Merit Dump File||· WINS/NBT Node Type|
|· DNS Domain Name||· NetBIOS Scope ID|
|· Swap Server||· XWindow System Font|
|· Root Path||· XWindow System Display|
|· Extensions Path||· NIS+ Domain Name|
|· IP Layer Forwarding||· NIS+ Servers|
|· Nonlocal Source Routing||· Boot Server Host Name|
|· Policy Filter Masks||· Bootfile Name|
|· Max DG Reassembly Size||· Mobile IP Home Agents|
|· Default IP Time-to-Live||· Simple Mail Transfer Protocol (SMTP) Servers|
|· Path MTU Aging Timeout||· Post Office Protocol (POP3) Servers|
|· Path MTU Plateau Table||· Network News Transfer Protocol (NNTP) Servers|
|· MTU Option||· World Wide Web (WWW) Servers|
|· All Subnets Are Local||· Finger Servers|
|· Broadcast Address||· Internet Relay Chat (IRC) Servers|
|· Perform Mask Discovery||· StreetTalk Servers|
|· Mask Supplier Option||· StreetTalk Directory Assistance (STDA) Servers|
|· Perform Router Discovery||· Router Solicitation Address|
If you create a scope and later run out of IP addresses, don’t fret. You can create an additional scope and your new scope will assign IP addresses where your previous scope ended.
To define a scope using the Create Scope Wizard:
- From the Action menu, select New Scope to launch the Create Scope Wizard, and then click Next.
- Type a name and description of your scope (Figure C) and click Next.
- Enter the start and end IP addresses of your scope. Remember to also assign the appropriate subnet mask as well (Figure D). Click Next.
- This window is where you specify all of your static IP addresses to exclude from your scope (Figure E). Add any exclusions and click Next.
- Enter the amount of time the lease is active (Figure F) and click Next.
- The next screen asks you whether you want to configure your DHCP options now or later. For this article, we will select Yes, I Want To Configure These Options Now and click Next.
- Enter your domain name and add the IP addresses for your DNS servers as shown in Figure G.
- Enter the addresses of any WINS servers you configured on your network for resolving NetBIOS names into IP addresses, as shown in Figure H.
- Choose Yes or No to indicate whether to activate your scope. There is still more work to be done, so we will choose No, as shown in Figure I.
- Click Finish.
Some networks implement superscopes, which are collections of scopes that are grouped to allow multiple logical subnets on one physical network. For more information on creating superscopes, see Microsoft’s article Q161571: “Using DHCP ‘Superscopes’ to Serve Multiple Logical Subnets.”
In addition to specifying exclusions, you can add reservations to your DHCP server. By adding a reservation, you ensure that a machine always receives the same IP address from the DHCP server.
To add a reservation:
- From the DHCP console, click the + sign next to the scope you created.
- Click Reservations and select Action | New Reservation, as shown in Figure J.
- Enter a friendly name for the reservation and the IP address you want to assign to the computer or device.
- Enter the MAC address of the computer or device. (For Windows NT/2000 machines, you can find the MAC address by running ipconfig/all from the command prompt of the machine.)
- Enter a description and then choose the following reservation type: DHCP, BOOTP (going across a router), or both, as shown in Figure K. Click Add.
Authorizing the DHCP server and activating scopes
Remember that after you install and configure your DHCP server, you will need to authorize your scope before it can be activated. Authorizing your DHCP server allows you to prevent hackers from configuring rogue DHCP servers.
To authorize your DHCP server:
- From the DHCP console, click on the DHCP icon.
- From the Action menu, select Manage Authorized Servers, as shown in Figure L.
- Click Authorize and enter the name or IP address for your server (Figure M).
- Now you’re ready to activate your DHCP server and bring it online. Click the scope you created and choose Activate from the Action menu (Figure N).
After configuring DHCP, the easiest way to troubleshoot is to use Ipconfig from a command prompt in Windows NT/2000. To view all TCP/IP information on a machine. just typeipconfig/all from a command prompt. To release a DHCP lease, type ipconfig/release; to renew a lease, type ipconfig/renew.
On Windows 98 machines, you must use the Winipcfg utility to access TCP/IP information. You can access this utility by choosing Start | Run and typing winipcfg (Figure O). From there, you can click the Release and Renew buttons to access other options.