The printer worked yesterday and is 'offline' today, though nothing was touched. Nothing was touched — except the router quietly gave it a new address at 3 AM. Reservations end that entire category of ghost problem.
DHCP hands every device an address from a pool, on a lease. Phones and laptops thrive on that freedom. Infrastructure does not: a network printer, NAS, CCTV DVR, or a PC others connect to must be findable at the same address every day, or shares, scan-to-folder and camera apps break one lease at a time. The clean fix is not static IPs typed into each device — it is a reservation in the router, keyed to the device's MAC address.
Under Network → DHCP Server you will find the pool's start and end addresses — commonly 192.168.0.100 to 192.168.0.199. Decide the layout once: shrink the pool's start to free a small fixed block if you like order (for example pool from .110), so reservations live in .100–.109 and no DHCP guest ever collides with them. On TP-Link firmware, a reserved address should sit inside the LAN subnet and outside the active pool in this pattern, which keeps the router's own bookkeeping simple.
Reserve for anything others connect to: printers and scanners, the file-sharing PC or NAS, the DVR/NVR, a door-access or billing machine, and the router-managed access points. Do not reserve for every phone and laptop 'just in case' — a long reservation list becomes its own maintenance burden and teaches you nothing. Ten good reservations beat fifty hopeful ones.
Typing a static IP into the printer itself also works — until someone changes the router's subnet or the device is reset, and then the fixed address is wrong in a place nobody remembers setting. A reservation keeps the truth in one place (the router, backed up with your config file), and the device stays on plain automatic DHCP, so any technician can service it without a treasure hunt. Prefer reservations; reserve device-side statics for gear that must live outside DHCP entirely, like the router's own upstream partner equipment.
Five minutes of paperwork saves every future argument: a simple list of device, MAC, reserved IP and date, kept as a printed page with the router documents and a photo on the owner's phone. When a printer is replaced, its new MAC goes in the same reservation row and the register gets one edited line — the office never notices the swap.
See reservations being set on the real DHCP pages in the full AC1900 setup video.
▶️ Watch Full VideoYes — reserving the address it currently holds is the smoothest path: no device changes its address, nothing reconnects, and from that moment the lease becomes permanent. Just make sure the address sits in the block you planned for fixed devices, or accept the exception and write it on the register.
Two usual causes: the MAC was typed with one wrong character (copy it from the client list rather than the label photo), or the device never renewed after you saved — power-cycle the device itself. Also confirm the reservation is enabled, not just added, and that no second router or access point on the network is running its own DHCP server.
Count simultaneous devices, then double it for comfort. A home: the default hundred is plenty. A small office with staff phones, laptops, printers and guests: keep at least 80–100 pool addresses outside your fixed block; leases are short-lived by default so the pool recycles itself.