Dhcp

DHCP – Dynamic Host Configuration Protocol Exam relevance: DHCP appears in the IP Services domain (10% of the exam) as part of the "DHCP and DNS" topic. Expect multiple-choice questions on the DORA process, the ip helper-address command, and how DHCP works across routed networks — these are reliable exam fixtures. --- ## What Is DHCP and Why Does It Matter? DHCP (Dynamic Host Configuration Protocol) automatically assigns IP configuration to network clients, eliminating the need for manual static addressing. When a PC boots up with no IP address, DHCP hands it everything it needs: - IP address - Subnet mask - Default gateway - DNS server address - Lease duration Without DHCP, every device on a network would need a manually configured address — unscalable in any real environment. --- ## The DORA Process The core of DHCP is the four-step DORA exchange between client and server: | Step | Message | Direction | Description | |------|---------|-----------|-------------| | D | Discover | Client → Broadcast | "Is there a DHCP server out there?" | | O | Offer | Server → Client | "I can offer you this address and config." | | R | Request | Client → Broadcast | "I'd like to use that address, please." | | A | Acknowledge | Server → Client | "Confirmed — the address is yours." | > Why is the Request still a broadcast? Because the client may have received offers from multiple DHCP servers. Broadcasting the Request lets all servers know which offer was accepted (so others can reclaim their offered addresses). --- ## DHCP Across Routers: The ip helper-address Command Here is the critical exam concept: **DHCP…