What is DHCP? This animated computer networks video explains DHCP or Dynamic Host Configuration Protocol. It gives details of how DHCP works, DHCP DORA process, types of DHCP messages, and DHCP packet format. How DHCP server assigns an IP address to DHCP client? Explained in detail.

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DHCP stands for Dynamic Host Configuration Protocol and is used to assign TCP/IP settings to the end systems, like computers, dynamically if the automatic IP settings are enabled for them.

When a laptop, with automatic IP settings enabled, is connected to the internet the laptop runs DHCP protocol. As a result, the DHCP server assigns an IP address to your laptop. DORA process involves the transmission of four DHCP messages including Discover, Offer, Request and Acknowledgment.

Suppose we connect our computer to the internet. At that time, it does not have an IP address. So, the Laptop or DHCP client sends a DHCP Discover message to the DHCP server. In response, DHCP server sends an IP address in DHCP Offer message. DHCP client, then, ask the DHCP server to allocate the offered IP address for it with DHCP Request message. DHCP server then allocates an IP address to the DHCP client and sends a confirmation with DHCP Acknowledgement message. On receiving the acknowledgement, DHCP client configures TCP/IP settings in the OS so that the laptop can access the internet.

In the second case, the DHCP server is present in some other subnet. In such a case, the relay agent act as a middleman between DHCP client and DHCP server. DHCPDISCOVER messages from the client is received by the relay agent. As the relay agent knows the IP address of the DHCP server, so it unicasts the received message to the DHCP server and fills the GIAddr field with the IP address of the interface at which the relay agent has received the message. Gateway IP address gives information to the DHCP server about the subnet where the DHCP client is present. The DHCP server then reply with unicast DHCPOFFER message to the relay agent with an offered IP address based on the subnet information. The router then broadcasts the reply within the subnet. DHCP client receives the DHCPOFFER and then broadcasts DHCPREQUEST requesting to allocate the offered IP address. Router again unicasts this message to DHCP server. The server unicasts DHCPACK to the router. The router then broadcasts it within the subnet. DHCP client on receiving the DHCPACK message configures the TCP/IP settings and becomes ready to load the web pages.

DHCPNAK, DHCPRELEASE, DHCPDECLINE, DHCPINFORM are the other DHCP messages. Therefore, a total of 8 DHCP messages are involved in the DHCP process.

These are the messages which help your device to fulfil all the prerequisites needed to connect to internet and comes under Dynamic Host Configuration Protocol Process. #TechTerms

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