dhcp server

The Dynamic Host Configuration Protocol is used by computers for requesting Internet Protocol parameters, such as an IP address from a network server. The protocol operates based on the client-server model. DHCP is very common in all modern networks^[1] ranging in size from home networks to large campus networks and regional Internet service provider
networks. Most residential network routers receive a globally unique IP
address within the provider network. Within a local network, DHCP
assigns a local IP address to devices connected to the local network.

When a computer or other networked device connects to a network, its DHCP client software in the operating system sends a broadcast
query requesting necessary information. Any DHCP server on the network
may service the request. The DHCP server manages a pool of IP addresses
and information about client configuration parameters such as default gateway, domain name, the name servers, time servers.
On receiving a request, the server may respond with specific
information for each client, as previously configured by an
administrator, or with a specific address and any other information
valid for the entire network, and the time period for which the
allocation (lease) is valid. A host typically queries for this information immediately after booting,
and periodically thereafter before the expiration of the information.
When an assignment is refreshed by the client computer, it initially
requests the same parameter values, but may be assigned a new address
from the server, based on the assignment policies set by administrators.

On large networks that consist of multiple links, a single DHCP
server may service the entire network when aided by DHCP relay agents
located on the interconnecting routers. Such agents relay messages
between DHCP clients and DHCP servers located on different subnets.

Depending on implementation, the DHCP server may have three methods of allocating IP-addresses:

• dynamic allocation: A network administrator
  reserves a range of IP addresses for DHCP, and each client computer on
  the LAN is configured to request an IP address from the DHCP server
  during network initialization. The request-and-grant process uses a
  lease concept with a controllable time period, allowing the DHCP server
  to reclaim (and then reallocate) IP addresses that are not renewed.
• automatic allocation: The DHCP server permanently assigns an
  IP address to a requesting client from the range defined by the
  administrator. This is like dynamic allocation, but the DHCP server
  keeps a table of past IP address assignments, so that it can
  preferentially assign to a client the same IP address that the client
  previously had.
• static allocation: The DHCP server allocates an IP address based on a preconfigured mapping to each client's MAC address. This feature is variously called static DHCP assignment by DD-WRT, fixed-address by the dhcpd documentation, address reservation by Netgear, DHCP reservation or static DHCP by Cisco and Linksys, and IP address reservation or MAC/IP address binding by various other router manufacturers.

DHCP is used for Internet Protocol version 4 (IPv4), as well as IPv6.
While both versions serve the same purpose, the details of the protocol
for IPv4 and IPv6 are sufficiently different that they may be
considered separate protocols.^[2] IPv6 devices may alternatively use stateless address autoconfiguration. IPv4 hosts may use link-local addressing to achieve limited local connectivity.