Question

How can i open up tcp port 53 for non DNS traffic?

I can only seem to pass DNS traffic through on that port.


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Accepted Answer

Ignore me, it’s the same for EC2 so must be something my end

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I think I have the same problem. I cannot use 53 / udp port on my vps server for python “socket”. Please can you tell me a detailed help text on how to do it?

python socket, example script’s error output

Traceback (most recent call last):
  File "serverr.py", line 4, in <module>
    server_socket.bind(('0.0.0.0', 53))
OSError: [Errno 98] Address already in use

I’m security testing and the target is only allowed outbound 53. It’s not a binding problem as netstat doesn’t show anything listening and the same happens with a fresh EC2 also. I’ll dig some more tomorrow, but at least I know it’s not a digital ocean issue. Thanks

Hello,

I don’t think that it is a good idea to use the registered ports for anything custom, I would recommend avoiding using anything up to and including 1023, or over 49152. For your custom services, just pick up a port from 1024 to 49151.

But generally speaking, you need to make sure that nothing else is listening on that port before you could bind another service as you can not have more than 1 service listening on one port at the same time.

Is there a particular reason why you need to use 53 for anything else besides DNS?

Regards, Bobby