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Dynamic Host Configuration Protocol

The need for DHCP

Any protocol is essentially a software that runs on a specific computer and manages all the "talking" with other computers in the "protocol language". In order for the same software to run on different machines there is a need to initialize the protocol with parameters specific to that machine and to the local network before starting proper operation. Initialization can be done during booting (if the protocol is embedded in the operating system) or it can be triggered by a specific application (if the protocol is embedded into the application).

Take for example the TCP/IP protocol stack: first of all, the IP protocol needs to know the IP address of the computer. Moreover, it needs to know the network subnet-mask, IP-addresses of the default router, the printer, the DNS and perhaps some other servers etc.

Those parameters can be configured manually and locally for each and every computer. Using a mechanism like that introduces some problems:

  1. A lot of manual work is required by the network administrator, being time consuming and error prone.
  2. Keeping the parameters up-to-date is not a one-time effort. The amount of work increases with the changes in the net (e.g portable computers that change locations frequently introduce a lot of daily work for network administrators).
  3. A change in a parameter common to all the computers in a subnet (e.g: local router's address) forces changes in each computer on the net.
  4. Some systems may not have a permanent storage device (e.g. hard disk) to store the configuration parameters - in which case no local configuration can be considered.
  5. In cases of shortage in IP-addresses and a network that is changing frequently it can be a waist to give a computer (that may be out of the network for a while) a permanent address. A better approach will be to use common pool of addresses by a set of computers. Manual configuration give no easy way of doing so.

All those reasons lead to the need in an automated mechanism for TCP/IP protocols' configuration and DHCP is the currently most advanced mechanism for doing so.
The next section gives an overview of some other mechanism and the evolvement from them into the current DHCP.

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