DHCP is derived from the Internet standard BOOTP (RFCs 951 and 1084), which allows dynamic assignment of IP addresses as well as remote booting of diskless workstations. In addition to supporting the dynamic assignment of IP addresses, DHCP supplies all configuration data required by TCP/IP, plus additional data required for specific services.
As noted, this functionality simplifies tasks for the network administrator, who can now manually configure just one computer—the DHCP server. Whenever a new computer starts on a network segment that is served by the DHCP server (or an existing computer is restarted), the computer asks for a unique IP address and the DHCP server assigns one from the pool of available addresses.
As Figure 2 shows, this process requires only four steps:
-
The DHCP client asks for an IP address (a DHCP Discover message).
-
The DHCP Server offers an address (a DHCP Offer message).
-
The DHCP client accepts the offer and requests the address (a DHCP Request message).
-
The DHCP Server officially assigns the address to the client (a DHCP Acknowledge message).
Figure 2. DHCP Automates the Assignment of IP Addresses
The DHCP server places an administrator-defined time limit, called a lease, on the address assignment. Halfway through the lease period, the DHCP client requests a lease renewal, and the DHCP server extends the lease. As a result, when a computer stops using its assigned IP address (for example, upon relocation to another network segment), the lease expires and the address returns to the pool for reassignment.
|
