Configuring DHCP Using Cisco IOS - DHCPv4 using Cisco IOS - Cisco DHCP server

As explained in RFC 2131, Dynamic Host Configuration Protocol, DHCP provides configuration parameters to Internet hosts. DHCP consists of two components: a protocol for delivering host-specific configuration parameters from a DHCP Server to a host and a mechanism for allocating network addresses to hosts. DHCP is built on a client/server model, where designated DHCP Server hosts allocate network addresses and deliver configuration parameters to dynamically configured hosts. By default, Cisco routers running Cisco IOS software include DHCP server and relay agent software.
DHCP supports three mechanisms for IP address allocation:
• Automatic allocation—DHCP assigns a permanent IP address to a client.
• Dynamic allocation—DHCP assigns an IP address to a client for a limited period of time (or until the client explicitly relinquishes the address).
• Manual allocation—The network administrator assigns an IP address to a client and DHCP is used simply to convey the assigned address to the client.
The format of DHCP messages is based on the format of Bootstrap Protocol (BOOTP) messages, which ensures support for BOOTP relay agent functionality and interoperability between BOOTP clients and DHCP Servers. BOOTP relay agents eliminate the need for deploying a DHCP Server on each physical network segment. BOOTP is explained in RFC 951, Bootstrap Protocol (BOOTP), and RFC 1542, Clarifications and Extensions for the Bootstrap Protocol.