How should one go about choosing a default TCP/IP port for a new service?

Question

When developing an app that will listen on a TCP/IP port, how should one go about selecting a default port? Assume that this app will be installed on many computers, and th

Answer 1

Use iana list. Download the csv file from :

https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.csv

and use this shell script for searching for unregistred ports:

for port in {N..M}; do if ! grep -q $port service-names-port-numbers.csv; then echo $port;fi; done;

and put 2 numbers instead of N and M.

Answer 2

If by widely-used, you mean you want to protect against other people using it in the future, you can apply to have it marked as reserved for your app by IANA here

Answer 3

You probably want to avoid using any ports from this list (Wikipedia).

I would just pick one, and once the app is used by the masses, the port number will become recognized and included in such lists.

Answer 4

Go here and pick a port with the description Unassigned

Answer 5

First step: look at IANA listing :

There you will see at the tail of the list

"The Dynamic and/or Private Ports are those from 49152 through 65535"

so those would be your better bets, but once you pick one you could always google on it to see if there is a popular enough app that has already "claimed" it

Answer 6

As others mention, check IANA.

Then check your local systems /etc/services to see if there are some custom ports already in use.

And please, don't hardcode it. Make sure it's configurable, someway, somehow -- if for no other reason that you want to be able to have multiple developers using their own localized builds at the same time.