Written 4 Sep 2026. This is a how-to, not a product card.

Give the computer a fixed address when the router won't

Nest or an ISP gateway won't reserve DHCP. Set one stable number on Ubuntu Server so SSH and Pi-hole keep the same address after a reboot. You don't need a new router.

Prefer a reservation on the router when it offers one: keep the computer on the same address on common routers. Short generic pass: keep it on the same number. This page is the fallback when Nest, Google Wifi, or the ISP combo box has no clean reserve menu. Need the current number first? Find it on the house network.

Skip until the router path is blocked

If TP-Link, ASUS, eero, or Netgear already has Address Reservation / IP Binding, use that and leave Linux on automatic DHCP. Stop here. Only continue when you confirmed the gateway will not stick an address to this computer after a reboot.

What this is

A fixed address means the computer stops asking the router for a random number. You type the address, the gateway, and the DNS it should use. SSH keeps the same target. Pi-hole keeps the same target. You are not opening a port to the internet.

What you need

• SSH or a keyboard on the computer (Debian or Ubuntu Server)
• The address it already uses today (example 192.168.1.50)
• The router / gateway address (example 192.168.1.1)
• The ethernet interface name (often enp1s0 or eth0)
• About ten minutes, and a second device already logged in if you can — a bad edit can drop SSH until you fix it at the screen

Keep the number the computer already has. Don't invent a new one unless that number is already taken by another device.

1. Write down what works today

On the computer:

hostname -I

ip -br link

ip route | head

From hostname -I, take the house address (usually starts with 192.168. or 10.). From ip -br link, take the cable interface that shows UP — not lo, not a Wi-Fi name if you already moved to ethernet. From the route line that says default via, take the gateway. Prefix is almost always /24 on a house network. If you are unsure, stay on the address DHCP already gave you.

2. Back up the netplan file (Ubuntu Server)

Ubuntu Server stores the network plan under /etc/netplan/. List it:

ls /etc/netplan/

Copy the existing file before you edit. Example name 00-installer-config.yaml:

sudo cp /etc/netplan/00-installer-config.yaml /etc/netplan/00-installer-config.yaml.bak

Open it:

sudo nano /etc/netplan/00-installer-config.yaml

Debian without netplan is different — see the short note below. Don't mix a fixed address on Linux with a conflicting reservation on the router.

3. Put a fixed address in the plan

Replace the ethernet stanza with something shaped like this. Swap the interface name, address, and gateway for yours. Indentation matters in YAML — use spaces, not tabs.

network:
  version: 2
  ethernets:
    enp1s0:
      dhcp4: false
      addresses:
        - 192.168.1.50/24
      routes:
        - to: default
          via: 192.168.1.1
      nameservers:
        addresses:
          - 192.168.1.1

Use the interface from step 1, not a guessed eth0. DNS on this first pass can be the router. If this computer already runs Pi-hole, prefer 127.0.0.1 for nameservers on the Pi-hole host itself so it can still resolve while it serves the house. Haven't installed Pi-hole yet? That is the first useful thing.

4. Try it safely, then keep it

From a keyboard on the computer when you can:

sudo netplan try

It applies the plan, then waits. If SSH from the couch still works with the same address, press Enter to keep it. If you lose the link, wait — it rolls back when the timer ends. If try is missing on a very old box:

sudo netplan apply

Only use apply when you can reach a screen if the address goes wrong.

5. Check from the couch

On the computer:

hostname -I

ping -c 3 192.168.1.1

Swap in your gateway. Then from your laptop, SSH to the same number you wrote down. Prefer a cable for this computer: a cable beats Wi-Fi for the old PC. After a reboot, confirm the number did not wander: find it on the house network.

Debian without netplan

Some Debian installs still use /etc/network/interfaces instead of netplan. The idea is the same: turn off DHCP on that interface, set address, netmask, gateway. Example shape:

auto enp1s0
iface enp1s0 inet static
    address 192.168.1.50
    netmask 255.255.255.0
    gateway 192.168.1.1
    dns-nameservers 192.168.1.1

Then sudo systemctl restart networking, or reboot once with a screen attached. If your Debian box uses NetworkManager, set a manual IPv4 profile in nmtui instead of editing interfaces by hand.

If SSH dies after apply

Plug in a keyboard and screen. Restore the backup:

sudo cp /etc/netplan/00-installer-config.yaml.bak /etc/netplan/00-installer-config.yaml

sudo netplan apply

Check the interface name and the /24 prefix. A typo in the gateway is the usual way to keep a local address but lose the internet. Wrong interface name leaves the cable on DHCP while you edited a ghost name.

What this is not

This is not a reason to buy a new router on day one. It is not forwarding port 22. It is not a VPN. It is not typing a fixed address when the router already reserves cleanly. Prefer the router reservation when that menu exists.

What next

Point the house at Pi-hole when the router allows it: point common home routers at Pi-hole. Nest or ISP gateway still hides LAN DNS? Set one device: point a phone or laptop at Pi-hole when the router won't. Pi-hole not installed yet: the first useful thing. SSH still fussy: SSH from the couch.

Skip

• Skip this if the router already reserves the address cleanly.
• Skip inventing a new IP when the current one still works.
• Skip setting a fixed address and a conflicting router reservation at the same time.
• Skip forwarding port 22 on the ISP box.
• Skip buying mesh “so reservation works.”