5.3.1. DORA Process

💡 First Principle: A device joining a network has no IP address yet—so how does it ask for one? It shouts (broadcasts). DHCP uses a four-step handshake called DORA because neither side knows the other's address at the start. Each step narrows down the conversation from "anyone out there?" to a confirmed lease.

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Why is the Request a broadcast? Because the client might receive Offers from multiple DHCP servers. The broadcast Request tells ALL servers which offer was accepted—so the others can reclaim their offered addresses.

Lease lifecycle: Once a client has a lease, it doesn't go through full DORA again. At 50% lease time, the client sends a unicast Request directly to the server to renew. If renewal fails, at 87.5% it broadcasts a Request to any available server. If the lease expires completely, the client starts over with Discover.

Key ports: DHCP server listens on UDP 67, client sends from UDP 68.

⚠️ Exam Trap: The Discover and Request messages are always broadcast (even though the client already knows the server's IP after the Offer). The Offer and Acknowledge are typically unicast to the client's MAC address.