Dynamic Host Configuration Protocol (DHCP)

Dynamic Host Configuration Protocol (DHCP) is a client/server protocol that automatically provides an Internet Protocol (IP) host with its IP address and other related configuration information such as the subnet mask and default gateway. In DHCP, port number 67 is used for the server and 68 is used for the client.

DHCP allows a network administrator to supervise and distribute IP addresses from a central point and automatically sends a new Internet Protocol (IP) address when a computer is plugged into a different place in the network.

DHCP is an application layer protocol that provides:

• IP Address − Unique identifier for the device on the network

• Subnet Mask − Defines the network portion of the IP address

• Default Gateway − Router address for accessing other networks

• DNS Servers − Domain name resolution services

DHCP Four-Way Handshake Process

DHCP uses a four-step process called DORA (Discover, Offer, Request, Acknowledge) for IP address assignment:

Step 1: DHCP Discover

• Client broadcasts a DHCP DISCOVER message to find available DHCP servers

• Source address: 0.0.0.0, Destination address: 255.255.255.255

• Message contains client's MAC address and may include specific requests

Step 2: DHCP Offer

• DHCP server responds with a DHCP OFFER message containing an available IP address

• Includes configuration parameters like subnet mask, default gateway, and lease duration

• If multiple servers exist, client accepts the first offer received

Step 3: DHCP Request

• Client sends DHCP REQUEST message to accept the offered configuration

• Message is broadcast to inform all DHCP servers which offer was selected

• Contains the server identifier of the chosen DHCP server

Step 4: DHCP Acknowledge

• Selected server sends DHCP ACK message confirming the IP address lease

• Client can now use the assigned IP address and configuration

• Other servers return their offered addresses to the available pool

DHCP Lease Management

Advantages of DHCP

• Automatic configuration − Eliminates manual IP address assignment

• Centralized management − Network administrators control IP allocation from one location

• Conflict prevention − Prevents duplicate IP address assignments

• Efficient IP utilization − Addresses are recycled when devices disconnect

Conclusion

DHCP automates IP address assignment through a four-step DORA process, enabling centralized network management and preventing IP conflicts. It provides essential network configuration parameters and efficiently manages IP address leases, making it indispensable for modern networks.