What Is DHCP? How Devices Get IP Addresses Automatically

You've probably connected hundreds of devices to Wi-Fi networks in your life, and not once did you have to type in an IP address. That's because of DHCP — the Dynamic Host Configuration Protocol — a background service that hands out network settings automatically the instant a device joins.

What DHCP actually does

When your phone joins your Wi-Fi, a four-step conversation happens in milliseconds, often nicknamed DORA:

1. Discover — the phone broadcasts: "Is there a DHCP server here?"
2. Offer — the router replies: "Yes. How about 192.168.1.42?"
3. Request — the phone says: "I'll take it."
4. Acknowledge — the router confirms and records the assignment.

Along with the IP address, DHCP also delivers the subnet mask, the default gateway, and which DNS servers to use — everything a device needs to get online.

Leases: why assignments expire

DHCP addresses aren't permanent — they're leased, typically for 24 hours to a week. Before the lease expires, an active device quietly renews it (usually keeping the same address). If a device leaves, its address eventually returns to the pool for someone else. This recycling is why a house with one router can serve a decade of visiting phones without running out of addresses.

DHCP reservations: the best of both worlds

Sometimes you want a device to always get the same address — a printer, a NAS, a security camera. Rather than configuring the device manually, set a DHCP reservation in your router: it pins a specific IP to the device's MAC address. The device still uses automatic configuration, but always receives the same answer. This is more robust than setting a static IP on the device itself.

When DHCP goes wrong

• Two DHCP servers on one network (e.g. plugging a second router in backwards) hand out conflicting settings — some devices work, others mysteriously don't.
• Exhausted pool — if the router's range is too small, new devices can't get addresses.
• No DHCP response — devices fall back to a self-assigned 169.254.x.x address, a classic symptom worth recognising.

Note that DHCP only manages your private addresses. Your public IP — check it here — is assigned by your ISP through a separate process.

Frequently asked questions