Home > Articles

This chapter is from the book

Dynamic Host Configuration Protocol (DHCP)

By using the Dynamic Host Configuration Protocol (DHCP) service in Windows Server 2003, client systems can be automatically configured with IP addresses and other configurable parameters that allow them to operate on the network. To install the DHCP role on the server, refer to the "DHCP Server Role" section in Chapter 2, "Server Roles and Security."

After the server role has been established, you must authorize the DHCP server in Active Directory if it is installed on a member server. To do this, log in to the domain with administrative rights, run the DHCP MMC, and choose Action, Manage Authorized Servers from the menu. When the Manage Authorized Servers dialog box opens, you can then authorize the server.

DHCP and Domain Controllers

If you are installing the DHCP server role on a domain controller, the server should be automatically authorized the first time you add the server to the DHCP console. You can also use the Configure Your Server Wizard to install the DHCP role on your system, as outlined in Chapter 2, "Server Roles and Security."

Requiring DHCP servers from both the Windows 2000 Server and Windows Server 2003 families to be authorized in Active Directory introduces a certain level of stability to your network. Adding Active Directory authorization prevents Windows 2000 and 2003 servers from being brought online when they are not authorized and causing IP address allocation issues on the network.

The downside (for lack of a better term) is that nothing prevents Windows NT 4 DHCP servers, Unix DHCP servers, or hardware DHCP devices, such as routers that offer DHCP addresses, from being introduced onto the network.

Windows Server 2003 can provide IP addresses by using DHCP manual assignment, DHCP dynamic assignment, or Automatic Private IP Addressing (APIPA).


In actuality, the DHCP client service supplies IP addresses when it attempts to contact the DHCP server and cannot get a response. Also, no default gateway is assigned to clients when APIPA is used. Because of this, clients using APIPA are limited to their own subnet.

Manual IP address assignment and DHCP manual address assignment are actually two different things. For manual IP address assignment, an administrator or similarly delegated person manually enters a static IP address and other information, such as the subnet mask and default gateway, DNS server, WINS server, and so forth.

DHCP manual address assignment dynamically assigns the same specific IP address from a scope of addresses to a specific DHCP client each time the client starts up by using the DHCP service. This enables administrators to automatically assign a static IP address to these systems without actually having to set each system with all the parameters (default gateway, DNS servers, and so on), as with manual IP address assignment.

DHCP automatic assignment dynamically assigns randomly available IP addresses from available scopes to all DHCP clients each time they start up by using the DHCP service. This allows administrators to automatically assign IP addresses to clients without actually having to set all the parameters (default gateway, DNS servers, and so on) for each system, as with manual IP address assignment.

DHCP servers are usually set up with multiple scopes, called a superscope, to work side by side with other DHCP servers in the enterprise. The DHCP lease process begins over UDP ports 67 and 68 as a broadcast message from the client system. For DHCP clients to successfully contact DHCP servers on remote networks, the IP routers must be RFC 1542 compliant. These routers support forwarding DHCP broadcasts off the local subnet. If the routers are not compliant, a DHCP Relay Agent must be in use on that subnet.

The DHCP Relay Agent is available through the Routing and Remote Access MMC on Windows Server 2003 (see Figure 3.1). Systems configured in the role of a DHCP server should not be configured as DHCP Relay Agents because both services use UDP ports 67 and 68 and degrade each other's services if they are installed together. On a single subnet, there is no practical need to do this because the DHCP server should simply respond to user requests on the subnet.

Figure 3.1Figure 3.1 The first step in configuring the DHCP Relay Agent service in the Routing and Remote Access MMC.

Figure 3.2 shows the available routing protocols in the New Routing Protocol dialog box: DHCP Relay Agent, IGMP Router and Proxy, Open Shortest Path First (OSPF), and RIP Version 2 for Internet Protocol.

When a client first starts, it sends out a DHCPDISCOVER broadcast message to all addresses ( The message contains the client's hardware (MAC) address and hostname. (The client also sends this message when its original lease has expired and cannot be renewed.) All available DHCP servers that are configured to respond receive the DHCPDISCOVER broadcast and send a DHCPOFFER broadcast message back with the following information:

  • The client's hardware address

  • An offered IP address

  • Subnet mask

  • Length of the lease

  • A server identifier (the IP address of the offering DHCP server)

Figure 3.2Figure 3.2 You can add routing protocols through the New Routing Protocol dialog box.

The DHCP client selects the IP address from the first offer it receives and responds with a DHCPREQUEST broadcast message that includes the IP address of the server whose offer was accepted. All the other DHCP servers then retract their lease offers and mark those addresses available for the next IP lease request.

The DHCP server whose lease was accepted responds with a DHCPACK broadcast message, which contains the valid lease period for that IP address and other configuration information outlined in the scope, such as router information (default gateway), subnet mask, and so forth. After the DHCP client receives this acknowledgment, TCP/IP is completely initialized, and the client can use the IP address for communication.

Automatic Private IP Addressing (APIPA)

When a DHCP client sends out the DHCPDISCOVER broadcast message, it waits one second for an offer. If the client does not receive a response from a DHCP server, it rebroadcasts the request three times at 9-, 13-, and 16-second intervals, with a random offset length of 0ms and 1000ms. If an offer is not received after the four requests, the client retries once every five minutes.

Beginning with Windows 98, DHCP clients can configure themselves by using APIPA and the DHCP client service. After the four attempts to receive an IP address have failed, the DHCP client auto-configures its IP address and subnet mask using the reserved Class B network address and the subnet mask No default gateway is used, so systems that use APIPA are not routable.

The DHCP client tests for an address conflict to make sure the IP address it has chosen is not already in use on the network. To do this, it broadcasts its selection from the range to the local subnet. If a conflict is found, the client selects another IP address and continues this process up to 10 attempts.

After the DHCP client makes sure the address it has chosen is not in conflict with another system on the subnet, it configures its network interface with the IP address. The client then continues to check for a response from the DHCP server every five minutes. If a DHCP server becomes available, the client drops its APIPA settings and uses the address the DHCP server offers at that time.

DHCP Relay Agent

When a DHCP client request for an IP address hits a non-RFC-1542– compliant router (meaning that the DHCPDISCOVER broadcast message can't be forwarded off the subnet), it fails to receive a response because the DHCP server never receives the DHCPDISCOVER broadcast message, and the client system configures itself with an APIPA address.

If a DHCP Relay Agent is in use on the subnet, it receives the DHCPDISCOVER broadcast message and forwards (routes) the message off the subnet to the DHCP server. Subsequently, when the DHCP server responds with an address and the DHCP client selects the IP address, the client responds with a DHCPREQUEST broadcast message that includes the IP address of the server whose offer was accepted. Again, this DHCPREQUEST broadcast message does not get out of this subnet unless a DHCP Relay Agent in use on the subnet can receive the DHCPREQUEST broadcast message and forward (route) the message off the subnet to the DHCP server.

Placement of DHCP Servers

DHCP servers should be located on at least one subnet on a LAN in a routed network. When the server needs to support clients on remote subnets separated by routers, the router should be RFC 1542 compliant, or a DHCP Relay Agent should be used to support forwarding DHCP traffic between the subnets.

When your network design allows more than one DHCP server to respond to requests, best practices dictate using the 80/20 rule, at a minimum, to divide the scope of addresses between the two DHCP servers. If Server 1 is configured to make available most of the addresses (approximately 80%) in the scope, Server 2 can be configured to make the remainder of the scope addresses (approximately 20%) available to clients.


The 80/20 rule for splitting addresses available in the scope can be tailored to meet your environment's addressing needs.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.


Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.


If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.


This site is not directed to children under the age of 13.


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020