How to use DHCP to configure your computer's TCP/IP network settings

Last revision January 9, 2009

DHCP stands for Dynamic Host Configuration Protocol. This is a method for automatically configuring TCP/IP network settings on computers, printers, and other network devices.

Using DHCP, the computer user never has to make any TCP/IP settings. Instead, his computer automatically communicates with a DHCP server on each network to which it connects. That server provides it with the appropriate settings to function on that network.

All modern computers, printers, and other devices come pre-configured to use DHCP. If you have altered this default condition, select your device operating system from the table on the left to get detailed instructions to reset it to use DHCP. If your device is not listed, consult the instructions that come with it, or contact the network administrator for assistance

Besides making life easier for the computer user, DHCP allows the network managers to make changes in the network intrastructure that automatically propagate to all devices. Because of these dual benefits, any device that supports DHCP (which includes all Windows and Macintosh computers) must use it as the TCP/IP configuration method on the Earth Sciences network. Manual configuration is prone to errors and obsolescence and should only be used where absolutely necessary.

Many Internet Service Providers use DHCP in a truly dynamic fashion. Each time your computer connects to its network, it gets a randomly assigned IP address from a pool of valid addresses.

Stanford University does not provide such random IP address assignments for wired ethernet service. Rather, the network registration process reserves a fixed, static IP address mapped to the unique ethernet hardware address of that device. This IP address is only valid on the network where the device was registered.

When a device connects to the Stanford wired network, it broadcasts its ethernet hardware address as part of its request for DHCP service. The campus DHCP servers match that hardware address to the registration database, and then provide the reserved IP address and appropriate router and name server addresses to the device. If the device is not registered, the DHCP servers give it a temporary private address that can only be used to reach the servers for the self-registration system.

The campus wireless network is different: although your computer must be registered, there is no fixed IP address assigned to it. The DHCP servers give it a random IP address in a range reserved for the wireless network. If your wireless interface is not registered, the DHCP servers give you a temporary private address that can only be used to reach the login page for the wireless guest service.

A device also gets a random IP address when you move it to another wired network on campus outside its home network (assuming you have requested the roaming attribute) or create an encrypted channel from an outside network to the Stanford network using the Stanford VPN client.

When using DHCP, keep in mind that because the protocol is designed to support dynamic assignment, each IP address assignment is for a limited time period, called a "lease". When the lease expires, the client device must contact the DHCP server again to renew it. The DHCP server has the option to provide a different IP address at renewal (not done at Stanford). The normal lease time on the Stanford network is 48 hours; after 24 hours, the client device will attempt to renew for another 48 hours.

If you move your computer from one network to another on campus, and it continues to try to use its old DHCP lease information, it will not work on the new network. In such a case, you must force it to renew the DHCP lease.

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