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Web & Networking › Networking Fundamentals

DHCP

How devices get an IP address automatically when they join a network.

Backend Engineer · Mid-levelData Engineer · Mid-level

Also known as: DHCP, dynamic host configuration protocol, dhcp lease

DHCP (Dynamic Host Configuration Protocol) is how a device joining a network automatically receives its IP address, subnet mask, gateway and DNS servers — instead of someone configuring each device by hand. Your laptop on office Wi-Fi, a VM booting in the cloud, a container starting up: all typically get their network identity from DHCP.

The exchange is a short broadcast conversation — discover, offer, request, acknowledge — and the address comes as a lease: valid for a period, renewed periodically, and reclaimable when the device leaves.

device: "who am I?" → DHCP server: "you're 10.0.4.27, gateway 10.0.4.1, DNS 10.0.0.2"

Why it matters to backend engineers: cloud instances, containers and office networks all depend on it, and “no network” on a fresh machine is often a DHCP failure. Servers that must keep a stable address use a static assignment or a DHCP reservation instead.

The classic mistakes:

  • Assuming a server’s IP is stable. A DHCP-assigned address can change across reboots unless reserved. Never hard-code a DHCP address into configs or firewall rules; use names or reservations.
  • No reservation for infrastructure. Anything others depend on — a database, an internal service — should have a static IP or a DHCP reservation so its address doesn’t drift.
  • Ignoring lease expiry. A device that can’t renew loses its address. Short leases on unstable networks cause flapping; misconfigured lease times cause mysterious drops.
  • Rogue DHCP servers. An unauthorised DHCP server on the network hands out wrong gateways or DNS, redirecting traffic. It’s a real attack and a common accident (someone plugs in a home router).
  • Confusing it with DNS. DHCP assigns the device’s own address; DNS resolves other names to addresses. Both must work for anything to connect.
  • Forgetting it in containers and VMs. Virtual networks run their own DHCP (or equivalent IPAM); “container has no network” is frequently an IPAM/DHCP-range problem, not your code.

How to think about it: DHCP is the network’s onboarding desk — automatic, leased, renewable. Fine for clients and ephemeral workloads; infrastructure that others address needs the stability of a static assignment or reservation.