Some devices need a predictable local address. A printer may be saved on several computers, a NAS may hold your backups, or a home server may be named in an automation. If that address changes, the service can look broken. The device itself may still be working fine.
The usual fix is a DHCP reservation, sometimes called an address reservation or static lease. It tells the router's DHCP server to offer a chosen address to a specific client. That is different from setting an address manually on the device. An address that looks unused today may already be in the DHCP pool and be assigned to another device later, so the distinction matters.
This guide is for a network you own or are authorized to administer. Router menus vary. A reservation also won't guarantee uninterrupted access: Wi-Fi coverage, power, DNS, VLAN rules, or the service running on the device may still be the real problem.
DHCP leases and client identities
On a typical home network, the router runs a DHCP server. A client asks for network settings, and the server gives it a lease containing at least an IP address for a limited time. DHCP identifies the client by a client identifier or, commonly in home-router interfaces, the MAC address of its network interface. The protocol calls this association a binding. The server manages it; the client does not own it permanently. RFC 2131
This explains a couple of common surprises. A device can get a different address when its lease expires, when it reconnects, or when the router decides the old address is no longer appropriate. And an old lease can stay in the router's device list after the device goes offline. A listed address is useful evidence, but it doesn't prove the device is reachable right now.
A DHCP reservation tells the server what to do with future leases: when this client asks, offer this address. It is usually safer than setting a static address on the device because the router remains the single place that allocates addresses. It also helps with troubleshooting later. The reservation records the intended assignment at the DHCP server, rather than leaving you to guess from a one-time scan.
A stable device identity
Before creating a reservation, check that you have the right network interface. A NAS with Ethernet and Wi-Fi can have two different MAC addresses. A laptop using a USB Ethernet adapter can change identity when you swap the adapter. A reservation for the Wi-Fi address won't help once the device is plugged into Ethernet.
Use two independent details where possible: the device's name or physical location, plus the MAC address currently shown by the router or the device itself. Copy the address with its separators exactly as the router displays it. Don't rely on a label alone. Generic names such as “android” or “unknown” are often reused.
Private Wi-Fi addresses need a closer look. Apple documents that its devices can use a private Wi-Fi address for each network, and that address can rotate in some circumstances. A reservation tied to a changing Wi-Fi address may stop matching the device later. Before relying on a MAC-based reservation, check the private-address setting for that specific network. Understand the privacy consequence before changing it. Apple: private Wi-Fi addresses
For equipment that needs to be reliably reachable, a wired interface or a documented, stable Wi-Fi identity is often easier to manage. That's a choice about managing that equipment, not a reason to disable privacy settings on every personal device.
Address selection without conflicts
Open the router's DHCP or LAN settings and note three things before changing anything:
- The local subnet, such as
192.168.1.0/24. - The DHCP pool, for example
192.168.1.100through192.168.1.200. - Existing reservations and currently active leases.
Choose an address in the same subnet that isn't already assigned or reserved. Many routers allow reservations inside the normal DHCP pool. That's fine when supported: the router knows the address is set aside. Other interfaces recommend an address outside the automatic pool. Follow the router's own approach instead of mixing the two.
One unanswered ping doesn't mean an address is free. A sleeping client, a second DHCP server, an isolated VLAN, or a firewall can make an address look unused when it isn't. Start with the router's reservation and lease tables. If you have more than one router, mesh controller, or DHCP server, find the one serving the device's network before adding the reservation.
Reservation setup on the router
Look for the menu under Network, LAN, DHCP Server, or Address Reservation. TP-Link's current support instructions give one example: select the client or enter its MAC address, enter the IP address you want, enable the entry, and save it. Other vendors use different labels, but you need the same basic information. TP-Link: configure address reservation
Make one change at a time:
- Select the confirmed client or enter its MAC address.
- Enter the chosen unused address in the correct local subnet.
- Save or enable the reservation. In your network notes, record the device, interface, MAC address, chosen IP address, and date.
- Renew the DHCP lease on the device, or reconnect its network interface, only if doing so is safe for its current work.
- Check the router's current lease table after the device reconnects.
Don't reboot a NAS or a computer that's updating, backing up, or serving other people just to test an address change. After the normal reconnect, check the device's management page or local service if it has one. Saving the router entry successfully doesn't prove that every application using the old address has updated.
Verification from the right network
Once the client gets a new lease, check three separate facts:
- The router shows the intended address bound to the intended client identity.
- The device itself reports that same address on the expected interface.
- One authorized client on the same network can reach the relevant service by its intended name or address.
Each check catches a different kind of error. The router may have the right reservation while the device is still using an old lease. Or the device may have the right address, but a backup job still points to the previous address. Even with the correct IP assignment, a service can be unavailable.
For services that support one, prefer a local DNS name, mDNS name, or router-managed hostname to copying an IP address into every configuration. Names can make later renumbering easier, though they have dependencies of their own. Keep the reservation as the stable allocation record. Use a name where the service and network resolve it consistently.
Problems beyond the reservation
If the address changes again, compare the MAC address in the new lease with the one in the reservation. A mismatch usually means the device used a different interface or a private Wi-Fi address. If they match, check for another DHCP server and confirm that the reservation was enabled and saved. Also check whether the client is connecting to a guest or separate VLAN instead of the expected LAN.
If the address stays the same but the device is still unavailable, also verify its subnet mask, gateway, and DNS settings, including those supplied by DHCP. Then check the connection and service. Check link status, Wi-Fi signal, and power. Look at the device's own logs, DNS resolution, firewall rules, and the specific service. A reservation makes one variable predictable. It doesn't diagnose the rest of the path.
Remove old reservations when you retire a device or replace its network interface. A short note beside each active reservation prevents a future administrator from assigning a familiar-looking address to the wrong machine. That record is often more useful than a long router list of unlabeled historical leases.