DHCP, an acronym for Dynamic Host Configuration Protocol, is a protocol used to automatically assign a unique IP address to a device. DHCP allows a computer to join an IP-based network without having a pre-configured IP address. DHCP is a protocol that assigns unique IP addresses to devices, then releases and renews these addresses as devices leave and re-join the network. DHCP is also used to configure the proper subnet mask, default gateway, and DNS server information on the device. A computer, or any other device that connects to a network (local or Internet), must be properly configured to communicate on that network. Since DHCP allows that configuration to happen automatically, it's used in almost every device that connects to a network including ...view middle of the document...
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.
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 DHCP documentation, address reservation by Net gear, DHCP reservation or static DHCP by Cisco and Linksys, and IP address reservation or MAC/IP address binding by various other router manufacturers.