DHCP operates through a systematic four-step process known as DORA: Discover, Offer, Request, and Acknowledge.
- Discover:
The first step in the DHCP process is the “Discover” phase. When a device, let’s say your computer or smartphone, joins a network, it sends out a broadcast message to discover available DHCP servers. This broadcast, essentially a shout-out on the network, is akin to the device saying, “Hey, I’m here, and I need an IP address!” The message is sent to the DHCP server using UDP (User Datagram Protocol) on port 67.
- Offer:
Upon receiving the broadcast, the DHCP server responds with an “Offer.” This is the second step in the DORA process. The DHCP server, having heard the device’s request, offers a specific IP address along with other configuration information. This offer is broadcasted to the entire network, allowing multiple DHCP servers to compete in providing an IP address. The DHCP server sends its offer using UDP on port 68.
- Request:
Once the device receives one or more offers, it chooses the most appealing one and formally requests the offered IP address from the chosen DHCP server. This marks the “Request” phase. The device now sends a unicast message to the selected DHCP server, explicitly stating, “I accept your offer, please assign me this IP address.” This request is also sent using UDP on port 68.
- Acknowledge:
The final step in the DHCP process is the “Acknowledge” phase. The DHCP server, having received the device’s request, confirms the assignment of the requested IP address. It acknowledges the request by sending a unicast message back to the device, finalizing the configuration process. This acknowledgment, or “ACK,” is transmitted using UDP on port 67.
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