A device that worked fine and then, after a reboot or a while offline, can no longer be found by an app, a hub, or a port-forwarding rule has usually not broken. Its network address changed, and whatever was pointing at the old one didn’t get told. A DHCP reservation is the fix that stops the address from moving again.
Why an address that “just worked” stops working after a reboot
Your router’s DHCP service hands out IP addresses to devices from a pool, on a lease: a device gets an address and holds it for a set period, then renews it, typically getting the same one back. Most of the time this is invisible and nothing changes.
It stops being invisible when a device’s address does change: after a router reboot, when a lease genuinely expires while the device is offline and the address gets reassigned elsewhere in the meantime, or when the pool of available addresses runs low enough that the router assigns something different on renewal. Whatever previously cached that device’s old address (an NVR expecting a camera at a specific address, a bridge’s device list, a port-forwarding rule, a hub’s own internal record) keeps looking for the device where it used to be, not where it now is. The device itself may be working perfectly and simply unreachable at the address everything else still expects.
What a DHCP reservation actually does inside the router
A DHCP reservation ties a specific device’s hardware address (its MAC address, which doesn’t change) to a specific IP address inside the router’s own DHCP pool. The device still requests an address automatically the same way it always has (nothing changes on the device’s side), but the router now always hands that specific device the same address every time, according to Google’s own support documentation on the setting.
This is different from disabling DHCP for that device entirely. The device is still using DHCP; the router has simply been told to always answer its request the same way. That distinction matters for the next section.
Reservation vs a manually set static IP: the difference that matters
There are two ways to give a device a fixed address, and they are not the same thing.
DHCP reservation (router-managed): You tell the router, “this MAC address always gets this IP.” The device keeps requesting an address automatically as normal. If you replace the device entirely, the old reservation simply goes unused: nothing conflicts.
Manually set static IP (device-managed): You go into the device’s own network settings and manually type in a fixed IP address, bypassing DHCP entirely on that device. This works, but it’s managed in two places now (the device’s own setting and the router’s pool), and if the router’s DHCP pool isn’t configured to skip that address, another device could eventually be handed the same one by DHCP, creating a conflict that a reservation avoids by design.
Google’s guidance, echoed by independent networking writers, is that a DHCP reservation is the safer default for almost everyone: it’s centrally managed from one place (the router), it survives a device factory reset or swap cleanly, and it can’t collide with the automatic pool the way a manually typed static IP occasionally can.
What to check before you set one
A reservation is simple to set up, but two things are worth checking first to avoid creating a new problem while solving the old one:
- Confirm you’re reserving the address to the correct MAC address. Some routers list connected devices by name, which can be stale or mislabeled if a device was renamed or replaced. Cross-check the MAC address printed on the device or in its own app settings if the router’s device list looks uncertain.
- Pick an address outside your router’s automatic assignment range, if your router’s interface allows specifying one, so the reservation can’t later collide with an address the pool also considers available. Most consumer routers handle this automatically when you reserve through their built-in tool, but it’s worth confirming rather than assuming.
What this does not fix
A reservation solves exactly one problem: a device’s address changing when nothing about the device itself did. It does not fix a device that’s dropping off the network entirely, which is a connectivity problem rather than an addressing one. For that, work through the device, radio, router or cloud test first.
It also doesn’t fix a router that’s genuinely run out of addresses to hand out to new devices, which is a related but different problem: the pool being too small for how many devices you’re adding, rather than one device’s address moving around inside a pool that has plenty of room. That’s a distinct diagnosis from the one this article covers.
For a device that used to be reliable and has recently started dropping off the network, see why a smart device that was working starts dropping off. And if you’ve recently made changes to your Thread setup rather than a standard Wi-Fi device, checking whether IPv6 is disabled on your router covers a related but separate addressing issue specific to Thread border routers.
FAQ
How do I find a device’s MAC address to set a reservation?
It’s usually printed on a label on the device itself, or visible in the device’s own app under network or “about” settings. Your router’s connected-devices list will also show it next to each currently connected device.
Does setting a DHCP reservation require restarting the device?
Often, yes: many routers apply the reservation the next time the device requests or renews its address, which may mean disconnecting and reconnecting the device to Wi-Fi, or power-cycling it, for the change to take effect immediately.
Will a reservation survive if I reset my router?
No. A full router reset (as opposed to a simple reboot) typically clears DHCP reservations along with other router settings, so you’d need to recreate them afterward.
Can two devices end up with the same reserved IP by accident?
Only if you manually reserve the same address to two different MAC addresses, which most router interfaces will warn against or prevent outright.
Is a DHCP reservation the same as port forwarding?
No, though they’re often used together. A reservation just keeps a device’s local address fixed. Port forwarding is a separate setting that lets traffic from outside your network reach a specific device, and it typically depends on that device having a fixed address to point to: which is exactly why the two are often mentioned in the same breath.
Sources referenced in this article
- Google, Set DHCP IP reservation or a Static IP address for a device.
https://support.google.com/googlehome/answer/6274660?hl=en(accessed 2026-08-06). Source of the reservation-vs-static-IP distinction, the MAC-to-IP mechanism, and the device-discovery/port-forwarding use cases. - Stephen Wagner, Static IP vs DHCP Reservation.
https://www.stephenwagner.com/2019/05/07/static-ip-vs-dhcp-reservation/(accessed 2026-08-06). Source supporting the guidance that a router-managed reservation is generally the safer default over a device-side manual static IP.
Review interval: 12 months (router-interface and firmware behavior).