What Is DHCP?
Every device on a network needs an IP address to communicate — it is the device's address for sending and receiving data. DHCP (Dynamic Host Configuration Protocol) is the system that handles IP address assignment automatically. Without it, you would have to manually configure a unique IP address on every device before it could access the internet.
How DHCP Works — The 4-Step Process
When a device connects to your network (phone joins WiFi, laptop plugged into Ethernet), a four-message exchange called DORA happens in milliseconds:
| Step | Message | What Happens |
|---|---|---|
| 1 | Discover | Device broadcasts: "Is there a DHCP server? I need an IP address" |
| 2 | Offer | Router responds: "Here, take 192.168.1.105 — it's available" |
| 3 | Request | Device confirms: "Yes, I'll take 192.168.1.105" |
| 4 | Acknowledge | Router confirms: "It's yours for 24 hours. Also, your DNS is 1.1.1.1 and your gateway is 192.168.1.1" |
The router also provides the subnet mask, default gateway, and DNS server addresses in the Acknowledge message — everything the device needs to communicate on the network and reach the internet.
DHCP Leases — Temporary IP Assignments
A DHCP lease is a time-limited assignment. Common lease durations:
- 24 hours — Common for home routers; a device must renew after 24 hours
- 7 days (168 hours) — Common on enterprise networks; devices roaming in and out of range
- 1 hour — Common on public WiFi (cafes, hotels) to recycle IPs for high device turnover
A device automatically renews its lease when it reaches 50% of the lease duration. If a device goes offline without renewing and the lease expires, the IP returns to the available pool. The device gets an IP again when it reconnects — it might get the same one (if it was not reassigned) or a different one.
DHCP Address Range
Your router's DHCP server only assigns addresses from a configured range called the DHCP pool. On most home routers, this is something like 192.168.1.100 to 192.168.1.254 — 155 addresses available for automatic assignment. The router itself is typically at the .1 address (192.168.1.1), outside the DHCP pool.
You can see the current DHCP pool and change it in your router's admin panel:
| Brand | Location |
|---|---|
| NETGEAR | Advanced → Setup → LAN Setup → DHCP Server |
| TP-Link | Advanced → Network → DHCP Server |
| ASUS | LAN → DHCP Server |
| Linksys | Local Network → DHCP Server Settings |
DHCP Reservations — How to Give a Device a Permanent IP
A DHCP reservation (also called static DHCP, address binding, or IP-MAC binding) permanently maps a device's MAC address to a specific IP. Every time that device connects, it gets the same IP — without any manual configuration on the device itself. This is the recommended way to give a stable IP to printers, NAS drives, cameras, game consoles, and servers.
How to set a reservation on each brand:
| Brand | Location |
|---|---|
| NETGEAR | Advanced → Setup → LAN Setup → Address Reservation → Add |
| TP-Link | Advanced → Network → DHCP Server → Address Reservation → Add |
| ASUS | LAN → DHCP Server → Manually Assigned IP around DHCP list → Add |
| Linksys | Local Network → DHCP Reservations → Add |
| D-Link | Setup → Network Settings → Add DHCP Reservation |
You need the device's MAC address to create a reservation. Find it in your router's connected devices list, or on the device itself (usually in Settings → About → WiFi address or via ipconfig /all on Windows).
Static IP vs DHCP Reservation — Which to Use
| Approach | How | Pros | Cons |
|---|---|---|---|
| DHCP reservation | Set in router, device stays on DHCP | Centrally managed, easy to change, device needs no reconfiguration | Requires router access to modify |
| Static IP (manual) | Set directly on the device | Works even if router DHCP changes, no router access needed | Must configure on each device, can conflict with DHCP pool if not careful |
For most home users, DHCP reservations are the better approach. Set a static IP directly on the device only when you do not have router access or need the device to maintain the same IP regardless of which router it connects to.
Common DHCP Issues
"DHCP server not responding" / "No IP address" error: The device connected to the network but did not get an IP from the router. Causes: router DHCP server is off (check LAN settings), DHCP pool is exhausted (too many devices — increase the pool range), device-side issue (disable/re-enable the network adapter), or a bad cable/WiFi connection prevented the DORA exchange from completing.
IP conflict ("Address already in use"): Two devices have the same IP address. Most common cause: a device with a manually-configured static IP that falls inside the DHCP pool. Either move the manual static IP outside the DHCP pool range (e.g., use 192.168.1.2–192.168.1.99 for static devices if the pool starts at .100), or use a DHCP reservation instead of a static IP.
Device getting a 169.254.x.x address: This is an APIPA (Automatic Private IP Addressing) address — the device assigned itself an address because DHCP failed. The device cannot reach the internet with this address. Check the physical connection, verify the router's DHCP server is enabled, and power cycle both the device and the router.