The Dynamic Host Configuration Protocol, or DHCP, is a method enabling network administrators to configure network software on computers on the network without physically visiting them. The DHCP server is the computer that holds the programs operating the protocol and fields incoming messages from computers on the network undergoing the process of being configured.
Configuration means "set up." It is a process of putting values into a program to enable it to operate in a certain way. The DHCP system is particularly concerned with allocating IP address to computers on the network, and so the network software on each computers has its IP address saved in its settings. An IP address is a form of address usually used to communicate across networks, to send data to a far-off place. No computer can be contacted over the Internet without an IP address. "IP" stands for Internet Protocol, which is the standard that defines the address structure.
Dynamic IP Addresses
The main purpose of DHCP is to manage dynamic IP addresses on a large network. A dynamic IP address is not permanently assigned to a computer. The company maintains a pool of fewer IP addresses than the number of computers on the network. This is because it is assumed that not all the computers will be switched on at the same time and so not all will be using an IP address simultaneously.
A DHCP client program, installed on each computer on the network, runs as part of the computer's start-up routine. Until it has an IP address, the computer cannot communicate with any other computer on the network, except for the DHCP server. The client program sends a request message to the DHCP server, which returns an IP address. The server notes the allocated IP address in a table and registers it against the client's MAC address. A MAC address is the physical address of a computer on a network. The lookup table that maps between these two addressing systems is organized according to the Address Resolution Protocol.
DHCP has two other configuration modes: automatic allocation and static allocation. Automatic address allocation records the first IP address allocated to a particular MAC address and then allocates the same IP address to that computer every time it boots and requests an IP address. Static address allocation is similar, except that the network administrator first fills in the IP address/MAC address table manually and the DCHP host only assigns the designated IP address to the computer with the MAC address matching an entry in the table. The difference between automatic and static allocation is that with automatic allocation the IP address allocated is the next available address from a pool; with static allocation, all IP addresses are preassigned. These two allocation methods are rare. In fact, not all DHCP servers support static allocation.
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