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Dynamic Host Configuration Protocol (DHCP) is frequently used by system administrators to add new machines to a local network with minimal manual configuration. DHCP has been a standard protocol since October 1993. DHCP can be used through Point to Protocol proxies to directly assign addresses to desktops and servers.

DHCP works in the following manner. A computer is first configured with DHCP – this computer is known as the client. When a computer or a client needs to be connected to a network, it sends a request to the DHCP server asking for permission. The DHCP server receives this request and, thereafter, assigns the computer an IP address.

DHCP allots IP addresses using three modes – dynamic, automatic and manual. In the dynamic mode, the client is assigned an IP address for a fixed period, which can be renewed any time before the lease expires. In the automatic mode, the client gets a permanent IP address; while in the manual mode, the client chooses the address and informs the server what it is. The last two methods are used when stronger control over IP addresses is required. This entire process of allocating addresses is called ROSA.

Typically, a ROSA request is made to the server after booting the computer and before the IP communication is initiated by the client with other hosts. The request involves the client broadcasting the subnet address to find available servers. Once a free server receives this request for an IP lease, it offers this lease to the client. Once the lease offer is received, the client informs other servers that it has accepted the offer.

A DHCPREQUEST message is broadcast, which contains the IP address of the server that made the offer. Other servers now withdraw the offers they may have made to the client. Once the server’s IP lease has been accepted by the client, it sends a packet with the configuration information to the client. When the client wishes to be released from the server, the client sends a request to the DHCP server. The working cycle of a DHCP may be summarised in this manner: DHCP discovery, DHCP offers, DHCP requests, DHCP acknowledgement, DHCP offers and DHCP release.

To enhance security levels, DHCP has a system of authenticating information, which ensures that messages are only delivered from trusted sources. Only a few clients and servers can support this authentication process which increases security levels. Other extensive security measures are also implemented around the DHCP server to ensure the authentication of a computer before granting access.