While the introduction of the BOOTP network protocol was a welcome innovation for network administrators tasked with managing large numbers of computers on a network, it was the first attempt and a new and improved TCP/IP network protocol soon followed. This protocol is called Dynamic Host Configuration Protocol (DHCP). DHCP was not designed as a replacement for BOOTP, but an extension of its functionality.
How DHCP Works
As its name indicates, DHCP provides dynamic IP address assignment. What this means is that instead of having to rely on a specific IP address, a computer will be assigned one that is available from a subnet or "pool" that is assigned to the network. DHCP also extends BOOTP functionality to provide IP addresses that expire. BOOTP indirectly uses a form of leasing that never expired, but the term wasn't actually used until the introduction of DHCP. When DHCP assigns an IP address, it actually leases the identifier to the host computer for a specific amount of time. The default lease is five days, but a network administrator should evaluate their own particular circumstances to determine an appropriate lease.
In basic terms, the DHCP lease process works as follows:
- A network device attempts to connect to the Internet.
- The network requests an IP address.
- The DHCP server allocates (leases) the network device an IP address, which is forwarded to the network by a router.
DHCP updates the appropriate network servers with the IP address and other configuration information.
The network device accepts the IP address.
The IP address lease expires.
- DHCP either reallocates the IP address or leases one that is available.
- The network device is no longer connected to the Internet.
- The IP address becomes an available address in the network pool of IP addresses.
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What is a private IP address?
What is DHCP?