UDP 53


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Dec 3, 2023
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I have a small issue. I have a virtual server with Ubuntu Server 20.04.6, and I've installed a DNS server on it. However, it doesn't respond on UDP port 53. It only responds if I use the command "dig @109.XXX.3.X thenarbox.com +vc." Of course, I'm running the command from a different server. When any DNS server uses TCP port 53, everything works as expected, but there's silence on UDP. I'm not using the "ufw" firewall, and UDP port 53 is allowed in iptables as it should be. When I run the command "dig @109.XXX.3.X thenarbox.com" without +vc directly on the server where the DNS is installed, it works fine. The issue is that it doesn't respond remotely, and I receive a timeout message.

Does anyone know what might be the problem?

Thank you very much, Nikolexa

PS: Sorry, I forgot that this is a english speaks page :D
Last edited:

G'day Nikolexa, Welcome to Linux.org

I cannot help you with that problem...I have zero experience with servers.

However, there are many people here who do have that experience.

Firstly, edit your opening post to display your problem/question in English

The site is based on English, and the vast majority of members here speak and understand English

Good Luck
Actually, this looks like a networking question to me.
While that makes sense, that's an odd port for an ISP to block.

You can find inexpensive VPS options out there and some will be free for a period of time. I take it that you were trying to host this yourself on your own ISP? The days of an ISP allowing that sort of thing seem to be waning, though my thoughts are that it should be the opposite. The ISP should be enabling us to run services as they are a service provider, at least in theory.
If it works for any of your local computers, then your ISP isn't blocking it.
If it works for any of your local computers, then your ISP isn't blocking it.

I'm confused. What if they're connecting over the LAN, their private network? It could still be blocked by their ISP, meaning that they can't connect to it over their public IP address. For example, you might be able to connect to port 22 for SSH over your LAN but your ISP might block that port (even if you try forwarding it in your router).

I must be missing something.

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