DHCP (Dynamic Host Configuration Protocol) automates the assignment of IP addresses and other network configuration parameters to devices on a network, simplifying network administration.
Here's a breakdown of the process:
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DHCP Discover: When a device (DHCP client) joins a network and needs an IP address, it broadcasts a "DHCP Discover" message. This message essentially says, "Is there a DHCP server out there?"
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DHCP Offer: A DHCP server on the network receives the "DHCP Discover" message and responds with a "DHCP Offer" message. This offer includes:
- A proposed IP address
- The subnet mask
- The IP address of the default gateway
- The duration of the lease (how long the device can use the IP address)
- Other optional configuration parameters (DNS server addresses, etc.)
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DHCP Request: The client receives one or more DHCP Offers and chooses one (usually the first one it receives). It then broadcasts a "DHCP Request" message, specifically requesting the offered IP address from the chosen server. This broadcast is important because multiple DHCP servers might have responded with offers.
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DHCP Acknowledgment (ACK): The DHCP server that received the "DHCP Request" acknowledges the request with a "DHCP ACK" message. This message confirms that the client can use the offered IP address and provides any other configuration information. At this point, the client configures its network settings with the provided information.
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Lease Renewal: Before the lease expires, the client will attempt to renew its IP address lease with the DHCP server that originally granted it the address. This process involves sending a "DHCP Request" message directly to the server. If the server is available and willing to extend the lease, it responds with a "DHCP ACK" message, extending the lease duration. If the server doesn't respond, the client will eventually attempt to renew the lease in broadcast mode, similar to the initial DHCP Discover process.
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Lease Release (Optional): When a device no longer needs the IP address (e.g., it's shutting down or disconnecting from the network), it can send a "DHCP Release" message to the DHCP server. This informs the server that the IP address is now available for reassignment. This step is optional; if the client simply disconnects, the server will reclaim the IP address when the lease expires.
In summary: A device needing an IP address broadcasts a request. A DHCP server responds with an offer including an IP address, subnet mask, gateway, lease time and other settings. The device accepts, and the server acknowledges, completing the IP address assignment. The DHCP server then monitors the lease and reclaims the IP address when the lease expires or when notified by the device.
