Dynamic Host Configuration Protocol (DHCP) and network address management

DHCP is a standardised protocol that enables clients to be dynamically assigned with various configuration parameters, such as an IP address, sub-network mask, default gateway, and other critical network configuration information.

DHCP servers centrally manage such configuration data, and are configured by network administrators with settings that are appropriate for a given network environment. DHCP servers in turn communicate with DHCP clients through the use of DHCP messages.

DHCP supports three methods of IP address allocation:

1. Dynamic DHCP allocation 
2. Static allocation 
3. Dynamic BOOTP allocation

A network can use one or more of these methods. The network administrator can select which of the methods to use.

DHCP provides for both static and dynamic configuration of IP clients. Static configuration enables you to assign a specific IP address and configuration to a client with a specific Media Access Control (MAC) address. When DHCP assigns IP addresses dynamically, IP clients are assigned an IP address that is chosen from a range of available addresses. Dynamic address assignment can be deployed when an individual client does not require a specific, static address.

DHCP is based on the Bootstrap Protocol (BOOTP) and maintains some backward compatibility with it.

There are two primary differences, between DHCP and BOOTP that should be noted. First, DHCP defines mechanisms through which clients can be assigned an IP address for a finite lease period, allowing for reassignment of the IP address to another client later. Secondly, DHCP provides the mechanism for a client to gather other IP configuration parameters it needs to operate in the TCP/IP network.

Though BOOTP is a predecessor of DHCP, it is still a viable from of address management. The backward compatibility of DHCP ensures that, within a DHCP environment, BOOTP specific devices can be allocated IP addresses.

The management overhead of introducing new clients to a network is simplified as the majority of addressing is administered centrally at the DHCP server.

The task of introducing new sub-networks, or re-addressing portions, or the whole, of the network is also simplified through centralisation.

The flexibility of DHCP ensures that devices that do require static address, whether for authentication purposes or other reasons, can be managed centrally. Most products will allocate static addresses by device MAC address, though some products can also assign by username or workgroup.

There are numerous software and hardware solutions that provide DHCP functionality, but inherently it is the network operating system (NOS) that is the most commonly used resource. Most standard NOS offerings include DHCP functionality as standard.