Setting up a DNS server can feel like a win until your firewall blocks everyone out. By default, Ubuntu’s Uncomplicated Firewall (UFW) shuts down external requests. To get your DNS server up and running for the world, you need to open port 53. But here is the catch: you cannot just open UDP and call it a day.
Why You Need Both UDP and TCP
Most standard DNS queries use UDP because it is fast. However, when a response is too large, or during zone transfers, DNS automatically switches to TCP. If you only open UDP, your server will seem broken or slow to many users. You must open both.
The Universal UFW Commands
Open your terminal and run these two commands. This tells UFW to let global traffic through on port 53 for both protocols:
sudo ufw allow 53/udp
sudo ufw allow 53/tcpMake the Changes Live
UFW keeps running old rules until you tell it to refresh. Reload the firewall configuration to apply your new rules immediately:
sudo ufw reloadDouble-Check Your Work
Never assume a firewall rule worked just because the terminal didn’t error out. Verify the active rules with this command:
sudo ufw status verboseLook for lines showing 53/udp and 53/tcp marked as “ALLOW IN” from “Anywhere”. If you see them, your DNS server is officially open for business.
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