In order to access the internet, the requesting host must have an IP address. Manual configuration involves system administrators identifying an available IP address, assigning it to the individual device, defining device configuration parameters, and updating the DNS database by mapping the device name to the IP address. Instead, Dynamic Host Configuration Protocol (DHCP) streamlines this process—designed to reduce the amount of configuration required when using TCP/IP. DHCP allocates IP addresses to hosts within your network and provides all the required parameters for hosts to operate and share information.
DHCP is based on a client/server model where the client software runs on the device and server runs on the DHCP server. Once configured, a device automatically requests an IP address which is granted by the DHCP server as a lease (an IP address with the necessary configuration data and expiration). Before it expires, the device renews the lease to extend the expiration. If the device moves to a different subnet or the device can no longer reach the server, the current address expires and is available for reallocation by the DHCP server.
Network routers are often configured as DHCP relay agents to forward client messages to a central DHCP server that is configured with scopes for a group of subnets. The server grants leases from the scopes.
A scope contains a set of addresses, along with certain configuration parameters called DHCP options. Example DHCP options include IP addresses where a client can find DNS servers or a hostname which the client should use.
|You must define at lease one scope for each subnet for which you want to use dynamic addressing.|
Note: An individual DHCP server or a highly-available DHCP cluster does not support overlapping IP space. To support overlapping IP space, use more than one DHCP cluster—one cluster for each logical, non-overlapping network.