Router DHCP Not Assigning IP Addresses — 3 Fixes That Actually Work

When your router's DHCP server stops assigning IP addresses, everything connected to it — phones, laptops, printers, smart TVs — all end up with self-assigned 169.254.x.x addresses and no internet. I've seen this at least forty times in the past two years. A client last month had their entire office offline for two hours because the DHCP pool filled up with ghost devices. Here's how you fix it, starting with the most common cause.

1. The DHCP Pool Is Full — Most Common Cause

Every router has a limited range of IP addresses it can hand out. By default, most home routers use a range like 192.168.1.100 to 192.168.1.200 — that's 101 addresses. But here's the thing: every device that connects grabs one, and if they don't release it (or if the lease time is long), the pool fills up fast.

I had a client whose kid's laptop kept connecting and disconnecting, each time grabbing a new IP. The lease was set to 24 hours, so those old IPs didn't get freed. Within a week, the pool was full. Then no new devices could get an IP.

How to Fix It

1. Log into your router's admin page — usually 192.168.0.1 or 192.168.1.1. If you don't know the IP, check the sticker on the router or run ipconfig (Windows) or ifconfig (Mac/Linux) and look for the default gateway.
2. Find the DHCP settings — look for tabs named "LAN," "DHCP Server," or "Setup." On TP-Link routers, it's under Advanced > Network > DHCP Server. On Netgear, it's Advanced > Setup > LAN Setup.
3. Check the pool range — if it's set to something tiny like 192.168.1.2 to 192.168.1.50, that's only 49 addresses. Expand it. I usually set the start to 192.168.1.100 and end to 192.168.1.254 — that gives you 155 addresses. Leave a few at the low end for static IPs.
4. Reduce the lease time — change it from 24 hours to 1 hour. This forces devices to renew their leases more often and releases addresses when devices disconnect. For an office, 2 hours is fine. For a coffee shop, 30 minutes.
5. Save and reboot — the router will clear the old lease table on reboot. Then reconnect your devices.

2. Stuck DHCP Leases Confuse the Server

Sometimes the DHCP server itself gets confused. It has a lease table — a list of which IP address belongs to which device. If a device disconnects abruptly (power outage, Wi-Fi drops, kid unplugs the laptop), the lease might stay in the table as "active." The router then refuses to give that same IP to a different device, and if the table is full, it won't hand out any new ones.

This happened to a friend running a small retail store. Their point-of-sale system got a new IP, but the old one stayed in the lease table. After a week, the table had 20 ghost entries. The POS system couldn't connect anymore because the router thought those IPs were still in use.

How to Fix It

1. Log in to your router and find the DHCP lease table — it's sometimes called "DHCP Client List" or "Attached Devices." On Asus routers, it's under Network Map > Clients.
2. Look for old or duplicate entries — you'll see devices with names you don't recognize or IPs that match your current devices but with different hostnames. Write down the ones you're sure are current.
3. Manually delete the stale leases — most routers have a "Release" or "Delete" button next to each entry. If not, you can often do it by clearing the lease table entirely. On some routers, you can't delete individual leases — you have to reboot the router to clear the whole table.
4. Force renew on your devices — on Windows, run ipconfig /release then ipconfig /renew in Command Prompt (run as admin). On Mac, go to System Settings > Network > your connection > Renew DHCP Lease. On Linux, use sudo dhclient -r then sudo dhclient.

Pro tip: If you have a lot of smart home devices (Thermostats, light bulbs, plugs), they can clog the lease table fast. Set their lease time to 30 minutes. They're mostly idle and don't need long leases.

3. Router Firmware Bug or Corrupt DHCP Server

Less common, but nasty. The router's DHCP server can get corrupted by a bad firmware update, a power surge, or just years of running non-stop. I saw this on a Linksys WRT1900AC running firmware from 2017. The DHCP server just stopped responding. The router's web interface worked fine, but no device could get an IP.

Another scenario: your router's DHCP server is actually working, but it's assigning IPs outside the range you expect because of a bug. I once had a Netgear R7000 that started handing out IPs from 192.168.1.2 even though the pool was set to 192.168.1.100 — that broke static IPs I'd set for servers.

How to Fix It

1. Check the router's log — look for "System Log" or "Event Log" under Administration or Advanced. Search for "DHCP" or "lease." If you see errors like "DHCP server failed to start" or "IP pool exhausted" when it shouldn't be, that's a clue.
2. Update the firmware — go to the router manufacturer's support site, download the latest firmware for your exact model (check the version number on the bottom of the router), and upload it via the router's admin page under "Firmware Update" or "Router Update." Don't use the auto-update feature — it sometimes grabs beta versions.
3. Factory reset the router — this is the nuclear option. Use a paperclip to press the reset button on the back for 10 seconds while the router is powered on. This wipes all settings, including the DHCP configuration. After the reset, log in using the default IP and credentials (user: admin, pass: admin or password). Reconfigure your Wi-Fi and DHCP settings from scratch.
4. Test with a different router — if you have a spare router, swap it in. If DHCP works with the spare, your original router's DHCP server is dead. Time for a new router.

Quick-Reference Summary Table

If you've tried all three and still can't get an IP, check if you accidentally turned off DHCP (yes, I've done that before — thought I was being clever with static IPs and disabled the server). Also check if your modem is actually providing internet — sometimes it's not a DHCP problem at all, just a dead modem. But that's a different article.