DHCP Explained — Quick Leases, DORA, and Troubleshooting Cheatsheet

DHCP explained: a compact, practical guide for engineers and sysadmins who need to understand how devices get IPs and why that sometimes fails. Why this matters DHCP hands out IP leases and important settings (gateway, DNS). Misconfigurations cause APIPA addresses, scope exhaustion, or unreachable clients. Core concepts (at-a-glance) Roles: client (requests), server (offers/tracks leases), relay/agent (forwards broadcasts across subnets). DORA: Discover → Offer → Request → Acknowledge. Uses UDP ports 67 (server) and 68 (client). Leases: temporary IP assignments with renew timers (T1/T2) so addresses can be reused safely. Common options: default gateway (router), DNS servers, domain name, NTP, etc. Fast troubleshooting checklist Client shows APIPA (169.254.x.x)? Check reachability to DHCP server and relay/agent (ip helper-address). Scope exhaustion? Inspect lease table and excluded ranges; consider shortening lease time for busy networks. IP conflicts? Look for duplicate static assignme