DHCP • Dynamic Host Configuration Protocol does not require an administrator to add an entry for a computer into the database. • Instead DHCP is “plug-and-play” networking. The computer runs a client to • obtain configuration info from DHCP • obtain a permanent address if the computer is nonmobile.
DHCP • DHCP uses permanent address that are assigned to server computers and a pool of addresses that are allocated on demand. • Based on the computer’s entry in the server’s database, the DHCP decides the type of address to assign. • For dynamic addresses, the computers IP may change with each boot.
DHCP Considerations • When a system reboots, there is a flood of DHCP requests. This is handled by using a random wait time before transmitting an address request. • Caching allows the computer to save the DHCP server’s address in a cache on a permanent storage, and use the cache information on reboot once it has been validated.
Lease • DHCP uses the concept of a "lease" or amount of time that a given IP address will be valid for a computer. • The lease time can vary depending on how long a user is likely to require the Internet connection at a particular location. • It's especially useful in education and other environments where users change frequently. Using very short leases, DHCP can dynamically reconfigure networks in which there are more computers than there are available IP addresses
APIPA • Automatic Private IP Addressing, a feature starting with Windows 98 • If a DHCP client finds no DHCP server when it boots, it uses APIPA to automatically configure itself with an IP address from a range that has been reserved especially for Microsoft. • The IP address range is 169.254.0.1 through 169.254.255.254. The client also configures itself with a default class B subnet mask of 255.255.0.0. A client uses the self-configured IP address until a DHCP server becomes available.
Other References • http://www.webopedia.com • http://www.whatis.com • Computer Dictionary, Shnier • Microsoft 2000 help