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DHCP Server


The Need Of Windows DHCP Server For Large Scale Corporate Network Is A Must To Reduce The Complexity Of The IP Address Deployment To Clients

Together with Domain Name System (DNS), the Dynamic Host Configuration Protocol (DHCP) serves as a basic foundation of a Microsoft Windows Server 2003 network infrastructure. Windows DHCP server provides hosts with an Internet Protocol (IP) configuration needed to communicate with other computers on the network.

Windows DHCP server is an IP standard designed to reduce the complexity of administering these address configurations. By issuing leases from a central database, windows DHCP server automatically manages address assignment and configures other essential settings for your network clients.

  • When a Windows DHCP server is unavailable, such clients automatically adopt an alternate configuration or an Automatic Private IP Addressing (APIPA) address.
  • Windows DHCP server provides automatic assignment of IP addresses. The administrator needs to define the scope (the pool of IP addresses)
  • Clients lease addresses for a specific length of time from the Windows DHCP server. Once 50% of the lease has expired, the clients will attempt to renew the same IP address. The Windows DHCP server will renew addresses for another lease period.
  • The Windows DHCP server will tremendously time-save for the network administrator
  • One Windows DHCP server can serve multiple subnets through DHCP relay agents or bootstrap protocol (BOOTP) forwarding
  • Windows server 2003 can serve almost all DHCP clients including BOOTP clients. BOOTP clients are not turned on by default

Windows DHCP server Scopes

A DHCP scope is a pool of IP addresses within a logical subnet, such as 192.168.100.1 through 192.168.100.220 (please refer to our previous network configuration scenario about IP register), that the Windows DHCP server can assign to clients. Scopes provide the essential means for the Windows DHCP server to manage distribution and assignment of IP addresses and of any related configuration parameters to clients either on the wired network or the clients on the wireless network (the clients that use the wireless network adapters such as USB network adapters).

  • DCHP server scope specifies the range of addresses available for lease. An IP address within a defined scope that is offered to a DHCP client is known as a lease. Each lease has a specified duration, and the clients must periodically renew the lease.
  • An exclusion range can be set within the range of defined scope if you don’t want to lease to DHCP clients. Exclusion range assure that the Windows DHCP server does not offer the exclusion range to DHCP clients
  • One DHCP scope is for one subnet
  • One Windows DHCP server can serve multiple subnets
  • Can supply additional configuration options such as default gateway; DNS servers (commonly integrated with the domain controllers AD); WINS servers
  • Can reserve addresses by MAC address. This feature is good for servers; printers; and other devices that require static addresses
  • Server can hold scopes for remote subnets. Since DHCP is a broadcast based, while routers by default block the broadcast you can use either RFC 1542 compliant routers or DHCP relay agents to forward the broadcast.

Load balance rule

To provide fault tolerance for the DHCP service within a given subnet, you might want to configure two Windows DHCP servers to assign addresses for the same subnet. With two Windows DHCP servers deployed, if one Windows DHCP server is unavailable, the other Windows DHCP server can take its place and continue to lease new addresses or renew existing clients. For balancing Windows DHCP server use in this case, a good practice is to use the 80/20 rule to divide the scope addresses between the two Windows DHCP servers. If Windows DHCP server #1 is configured to make available most (approximately 80 percent) of the addresses, Windows DHCP server #2 can be configured to make the other addresses (approximately 20 percent) available to clients.

In a large corporate network infrastructure, the load balance windows DHCP server is very essential as backup strategy and redundancy. Not just windows DHCP server, connectivity to the Internet is also made redundancy.

How the process of Windows DHCP server to the clients?

  • DHCP clients broadcast DHCPDISCOVER packet to the network
  • Windows DHCP server then responds with DHCPOFFER packet
  • DHCP clients broadcast DHCPREQUEST packet
  • Windows DHCP server responds with DHCPACK packet
  • After 50% lease time, DHCP clients will attempt to renew address with a DHCPREQUEST directed to the Windows DHCP server
  • Windows DHCP server responds with DHCPACK again

Configuring the Client

To configure a client to receive its IP address information from a Windows DHCP server, open the Internet Protocol (TCP/IP) Properties dialog box for the appropriate network connection. By selecting the “Obtain an IP Address Automatically” option, you enable the client to obtain from the Windows DHCP server an IP address, subnet mask, and all DHCP options except for DNS options. To configure the client to receive DNS options from the Windows DHCP server, select the Obtain DNS Server Address Automatically option.

Migrating from APIPA or Alternate Configurations

If a client has already been configured to obtain an IP address and DNS server address automatically, and the network is not using ICS, you merely need to renew the IP configuration to apply the settings from the newly configured Windows DHCP server.

To renew a configuration, enter the ipconfig /renew command at the command prompt. Alternatively, you can restart the client computer, and the new IP configuration from Windows DHCP server is applied as the computer reboots.

Migrating from an ICS Connection

ICS is a shared dial-up connection on a server that provides Internet access to network clients and automatically configures client computers with an address in the 192.168.0.x subnet range. Because this service competes with the Windows DHCP server service, you should delete any shared (ICS-enabled) dial-up connections on the server and restart the server computer before installing the DHCP Windows component or adding the Windows DHCP server role.

The above procedure frequently will not work as expected. ICS clients are already configured to obtain an IP address automatically, so in theory, they require no reconfiguration beyond a simple reboot if you want to migrate to receive the IP from Windows DHCP server. However, you might find that in practice, ICS clients stubbornly cling to their ICS addresses even after DHCP is deployed. To prevent such complications, you can first apply a manual (static) address to the client computers after the ICS connection is deleted; this procedure breaks the ICS connection. Then restart the client computers. After the clients restart, they will migrate cleanly to receive the IP from Windows DHCP server as soon as you reconfigure them to obtain an address automatically.


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July 5th, 2009 | Tags: , , | Category: Network Infrastructure

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