Question

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

Posted on October 3, 2019
DigitalOcean Accounts Firewall
Asked by seang1

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

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seang1 • October 3, 2019

Accepted Answer

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

Bobby Iliev

Site Moderator

• October 3, 2019

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

seang1 • October 3, 2019

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