The error: New devices can't get an IP address. Existing devices keep working until their lease renews, then they drop off the network too. The DHCP server logs show the scope has no addresses left to hand out.
Environment: Windows Server DHCP role, any version.
Why this happens: Scopes are sized once, early, based on expected device count — and device count on most networks only grows (phones, IoT, guest devices). The scope quietly fills up over months until the day it's actually full, which always feels sudden even though the underlying growth wasn't.
The fix:
- Check actual scope utilization in the DHCP console (right-click the scope → view Address Pool / Leases) to confirm this is really exhaustion and not a different issue.
- Reduce lease duration temporarily if you need breathing room fast — shorter leases free up unused addresses faster.
- Clear stale/inactive leases: devices that left the network months ago sometimes still hold leases until they expire.
- Properly fix it by expanding the scope's address range, or splitting device types across additional scopes/VLANs (a real fix, not a workaround).
One thing worth knowing: shortening lease duration is a legitimate emergency lever, but doing it permanently just increases DHCP server chatter across your whole network for no lasting benefit — fix the actual scope size, then put lease duration back to something sane.