Dynamic Host Configuration Protocol DHCP, How DHCP work, DHCP tutorials, DHCP messages

Dynamic Host Configuration Protocol (DHCP) is used to dynamically (automatically) assign TCP/IP configuration parameters to network devices (IP address, Subnet Mask, Default Gateway, DNS server etc). Dynamic Host Configuration Protocol (DHCP) is described in RFC 1531. Other RFCs related with Dynamic Host Configuration Protocol (DHCP) are RFC 1534, RFC 1541, RFC 2131, and RFC 2132. DHCP is an IETF standard based on the BOOTP protocol. A computer that gets its configuration information by using Dynamic Host Configuration Protocol (DHCP) is known as a Dynamic Host Configuration Protocol (DHCP) client. DHCP clients communicate with a DHCP server to obtain IP addresses and related TCP/IP configuration information. DHCP server should be configured properly by the DHCP administrator.

How Dynamic Host Configuration Protocol (DHCP) Works?

The Dynamic Host Configuration Protocol (DHCP) client TCP/IP software is not configured with a static IP address and it is configured to obtain an IP address dynamically from a Dynamic Host Configuration Protocol (DHCP) Server. When a DHCP client device boots up, it not capable send and receive network traffic, because TCP/IP is not configured. But it can participate in broadcast traffic.

The process of leasing TCP/IP configuration from the Dynamic Host Configuration Protocol (DHCP) server involves four steps as listed below.

1. DHCPDISCOVER: The Dynamic Host Configuration Protocol (DHCP) client broadcasts a DHCP discover message on the network containing its MAC address and NetBIOS destined for UDP port 68 (used by BOOTP and Dynamic Host Configuration Protocol (DHCP) servers). This first datagram is known as a DHCPDISCOVER message, which is a request to any DHCP server that receives the datagram for configuration information.

2. DHCPOFFER: Each DHCP server on the network that receives the request responds with a DHCP offer message as broadcast (UDP port 67) to the computer that issued the DHCPDISCOVER. An offered the IP address and subnet mask is also included in the message. If the DHCP client device received multiple DHCPOFFER, the DHCP client accepts the first DHCP offer that arrives.

3. DHCPREQUEST: The Dynamic Host Configuration Protocol (DHCP) client accepts an offer and broadcasts a DHCPREQUEST datagram. The DHCPREQUEST datagram contains the IP address of the server that issued the offer and the physical address of the DHCP client. DHCPREQUEST message requests the selected DHCP server to assign the DHCP client an IP address and other TCP/IP configuration settings. DHCPREQUEST message also notifies all other DHCP servers that their offers were not accepted by the DHCP client.

4. DHCPACK: When the DHCP server from which the offer was selected receives the DHCPREQUEST datagram, it constructs a DHCPACK datagram. This datagram is known as a DHCPACK (DHCP ACKNOWLEDGEMENT). The DHCPACK includes an IP address and subnet mask for the DHCP client. It may include other TCP/IP configuration information like IP addresses for the default gateway, IP addresses for DNS servers, IP addresses for WINS servers etc.

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Dynamic Host Configuration Protocol (DHCP) - How DHCP Works?

How Dynamic Host Configuration Protocol (DHCP) Works?