📘 How to Change DNS on Debian 12

This guide explains how to change the DNS servers on a Debian 12 system. DNS (Domain Name System) is used to resolve domain names (like example.com) into IP addresses.

✅ Method 1: Temporary Change (for testing)

You can temporarily change DNS by editing the /etc/resolv.conf file directly. This change will be lost after reboot or network restart.

🔧 Steps:

Open the file with a text editor:
```
sudo nano /etc/resolv.conf
```
Add or edit nameserver entries. For example:
```
nameserver 1.1.1.1
nameserver 8.8.8.8
```
Save and exit (press CTRL+O, then Enter, then CTRL+X).
Test DNS resolution:
```
ping google.com
```

⚠️ Warning: On Debian 12, this file may be managed by systemd-resolved or the dhclient. So changes here might get overwritten.

✅ Method 2: Permanent Change (Recommended)

📍 Step 1: Create or Edit `/etc/systemd/resolved.conf`

sudo nano /etc/systemd/resolved.conf

Add or update the [Resolve] section like this:

[Resolve]
DNS=1.1.1.1 8.8.8.8
FallbackDNS=9.9.9.9

You can change the IPs to any DNS servers you prefer.

📍 Step 2: Restart systemd-resolved

sudo systemctl restart systemd-resolved

📍 Step 3: (Optional) Create a symlink for `/etc/resolv.conf`

If /etc/resolv.conf is not linked properly, link it to systemd-resolved:

sudo ln -sf /run/systemd/resolve/resolv.conf /etc/resolv.conf

Check the link:

ls -l /etc/resolv.conf

✅ Method 3: Change DNS via NetworkManager (if installed)

If your server uses NetworkManager, you can change DNS per connection.

List connections:
```
nmcli connection show
```

Set custom DNS:

nmcli connection modify <connection-name> ipv4.dns "1.1.1.1 8.8.8.8"
nmcli connection modify <connection-name> ipv4.ignore-auto-dns yes

Restart the connection:

nmcli connection down <connection-name> && nmcli connection up <connection-name>

📦 Common DNS Providers

Provider	DNS IPs
Cloudflare	`1.1.1.1`, `1.0.0.1`
Google	`8.8.8.8`, `8.8.4.4`
Quad9	`9.9.9.9`, `149.112.112.112`

✅ How to Verify Your Current DNS

Run the following command to check which DNS is being used:

systemd-resolve --status

Or check /etc/resolv.conf:

cat /etc/resolv.conf

🧼 Troubleshooting

If your DNS doesn't seem to update, make sure no other service (like dhclient or NetworkManager) is overwriting it.
Restart your networking or reboot the system if needed:
```
sudo systemctl restart systemd-networkd
```

MM25Zamanian/how-to-change-dns-debian12.md