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Dynamic Host Configuration Protocol (DHCP)

Networking Topics > Layer 3 Routing > Dynamic Host Configuration Protocol (DHCP)

DHCP is a popular method for dynamically assigning IP addresses on a network. This is achieved by using a DHCP server in a client-server configuration.

DHCP was created in collaboration with the Internet Information Task Force (IETF) and is supported in operating systems such as Windows, Linux and Unix variants and Mac OS. The DHCP server is configured with a range of IP addresses which it allocates to computers on the network as they boot up.

When a DHCP client boots it initialises the DHCP process and sends a request to the nearest DHCP server for an IP address, this request contains the MAC address (Physical address) of the machine requesting the IP.

Assuming the nearest DHCP server(s) has available IP addresses, it will respond with a DHCPOFFER message offering the lease of an IP address. During this negotiation the DHCP server will not attempt to issue this IP address to any other clients.

The client will select one of the DHCP offers and respond with a DHCPREQUEST to indicate that it has chosen to use that IP address. The DHCP server will then send a DHCPACK message confirming the selection.

The table below shows the DHCP lease process between the DHCP client and DHCP server.

Server	<-- DHCPDISCOVER	Client
	DHCPOFFER -->
	<-- DHCPREQUEST
	DHCPACK -->

After the DHCP server sends the DHCP ACK the client can start using it’s IP address.

DHCP can also be configured to send additional information such as the default gateway and DNS server details as well as the IP address and subnet mask.

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