DHCP (Dynamic Host Configuration Protocol) is a network protocol that enables devices to automatically obtain IP addresses, subnet masks, default gateways, and other network configuration parameters. It simplifies the process of configuring network settings for devices on a network. Here's a general overview of how DHCP works:
1. DHCP Discovery:
When a device (known as a DHCP client) joins a network, it sends a DHCP discovery message to find a DHCP server. This message is typically broadcasted to the local network and contains a request for IP configuration.
2. DHCP Offer:
DHCP servers on the network receive the discovery message and respond with a DHCP offer. The offer includes an available IP address, subnet mask, lease duration, and other configuration parameters. The DHCP server reserves the offered IP address temporarily, ensuring that no other client will receive the same address.
3. DHCP Request:
The client receives multiple DHCP offers from different servers (if available). It selects one offer and sends a DHCP request message to the chosen DHCP server, indicating its acceptance of the offered configuration.
4. DHCP Acknowledgment:
The DHCP server receives the request and verifies that the offered IP address is still available. If so, it sends a DHCP acknowledgment message to the client, confirming the IP address lease. The acknowledgment also includes additional network configuration information.
5. IP Address Lease:
The client receives the DHCP acknowledgment, indicating that it has successfully obtained an IP address. The client configures its network interface with the provided information, including the IP address, subnet mask, and other parameters. The lease duration specifies how long the client can use the assigned IP address before it needs to renew the lease.
6. Lease Renewal and Rebinding:
As the lease expiration approaches, the client can initiate a lease renewal process to extend the lease duration with the same DHCP server that originally assigned the IP address. If the original server is unavailable, the client can broadcast a DHCP request to any DHCP server on the network, starting a lease rebinding process. In this case, a new DHCP server may offer an extension or assign a different IP address.
7. Lease Expiration and Release:
If the client fails to renew the lease or if the lease duration expires, the IP address is released and returned to the DHCP server's available address pool. The client must repeat the DHCP discovery process to obtain a new IP address if it wants to remain connected to the network.
This sequence of DHCP messages allows devices to dynamically obtain network configuration information without manual configuration, making it efficient for managing IP address allocation in large networks.