An automation that worked for months stops one morning. Nothing was changed, yet the dashboard says a device is unreachable. After an hour of poking around you discover the device is fine; the router simply gave it a different address, and everything that pointed at the old one now points at nothing. This is among the most avoidable problems in home and small-site IoT, and the fix takes about twenty minutes per network.

Why Addresses Move

Most devices obtain their address automatically from the router through DHCP. The router hands out an address for a lease period, and when the lease expires or the device reconnects after a power cut, it may receive a different one. For a phone this is irrelevant. For a device that other things connect to by number, such as a camera feed, a printer, an MQTT broker, or a hub, a changing address breaks the link.

You have three ways to prevent that: set a fixed address on the device itself, reserve an address for it in the router, or stop depending on numbers by using names. For most people the second is best.

Reservation Versus Static Configuration

A static address configured inside the device works, but it hides the choice in every device’s settings. You can forget it, mistype it, or collide with another device, and if you later change your network plan you must visit each device. Many cheap IoT devices barely support static settings.

A DHCP reservation keeps the device on automatic configuration but tells the router to always hand it the same address, matched by its hardware identifier. The assignments live in one place, the router, so you can see and change them together. If the device is replaced, you edit one row. That central visibility is the real benefit.

Approach	Where set	Strength	Weakness
Dynamic DHCP	Nowhere	No effort	Addresses can change
DHCP reservation	Router	Central, easy to audit	Needs a router that supports it
Static on device	Each device	Works without router help	Easy to forget, risks conflicts
Names via local DNS	Router or DNS server	Independent of the number	Needs name resolution to work

Plan an Address Range First

Before reserving anything, look at how your router divides its address space. Typically one range is handed out dynamically, and you can carve out a separate block for reservations. Keeping reserved devices in a distinct block makes the table readable and prevents overlap with dynamic leases. A simple scheme might set infrastructure such as hubs and access points in one small block, fixed IoT devices in another, and leave the rest dynamic.

Write the scheme in a note. Even a short list of what lives in which block saves hours later. If you use separate networks for IoT, apply the plan per network, and remember that rules between networks refer to these addresses.

How to Reserve an Address

The steps vary by router, so check your router’s current documentation, but the pattern is the same. Open the router’s admin page and find the list of connected devices. Pick the device and choose the option to reserve or bind its current address, or enter its hardware identifier and the desired address manually. Save, then reboot or renew the device so it picks up the reservation. Confirm by checking the table afterward.

A trap worth knowing: many modern phones and some devices use randomized hardware identifiers per network. If a device changes its identifier, a reservation keyed to the old one stops matching. For fixed devices, turn off address randomization for your home network where that option exists.

Use Names Where You Can

Even better than remembering a number is using a name. Many routers register device names in a local DNS service, and some systems announce names automatically on the local network. Pointing your automation at a hostname rather than a numeric address makes it tolerant of change. Give devices short, meaningful hostnames and keep them consistent with your labels.

Be aware that name resolution can differ between apps and operating systems, and local names may not work across separate networks unless DNS is configured for it. Test from the machine that actually does the connecting, not just from your laptop.

Example: A Home Server Running Automation

Suppose a household runs a small server hosting their automation platform and message broker. Several sensors and a camera connect to it. After a power cut, the router restarts and hands out addresses in a different order, and the sensors lose the broker. The owner reserves an address for the server in a dedicated infrastructure block, then does the same for the camera and the hub. Sensors are reconfigured once to use the server’s hostname instead of the number. The next power cut passes unnoticed. Total effort: one evening, plus a note listing which address block holds what.

Avoid These Mistakes

Do not reserve an address inside the dynamic pool unless your router explicitly allows it, or it may be given to another device. Do not assign the same address to two devices; conflicts cause intermittent failures that are hard to diagnose. Do not forget to back up your router configuration after a lot of reservations, because a factory reset erases them. And do not reserve everything: only devices that others depend on need stable addresses.

For networks with security needs, remember that a fixed address is not a security measure. It is a convenience for stability. Real protection comes from network separation, firewall rules, and updates.

Frequently Asked Questions

Will a reservation survive a router reboot? Yes, reservations are stored in the router configuration. They are lost only if the router is reset or the configuration is not restored.

Do all devices need a fixed address? No. Devices that only reach out to the cloud rarely care. Prioritize anything others connect to.

What if my router does not support reservations? Consider running DHCP on a small dedicated server, using static settings on critical devices, or upgrading to a router with better controls.

Why does my device ignore its reservation? It may use a randomized hardware identifier, or hold an existing lease. Renew the lease or reconnect the device.

Is local DNS hard to set up? Often it is a single setting on the router. Others require a small DNS service, which is manageable but a bigger step.

Next Step

Log into your router, list the devices, and mark the three that other things depend on, such as a hub, a broker, or a camera. Reserve those three addresses tonight, and note them in a file you can find later.