I'm designing an application with it's own protocol and I need to choose a port for it, what port should I choose (or how should I decide what port to set as default for it)?

Any port that isn't already well known for being used with certain apps should be fine.

Take a look at /etc/services if you can to get a rough idea of what ports are most commonly used, already.

Take a look at /etc/services if you can to get a rough idea of what ports are most commonly used, already.

So if for example 96 port is not used there, can I use it?

If you want it to run on linux and not require root, you have to put it on a port higher than 1024.

You shouldn't use a privileged port. As far as I know, there's an 'official' registry of what services run on each privileged port. Yours probably doesn't qualify :p.

The IANA maintains the official registry of assigned ports (http://www.iana.org/assignments/port-numbers).

pick something nearer the top end, not iana assigned/registered and you wont go too wrong

Thank you, I decided to use a higher port and then implement http tunelling (if there will be a lot of troubles with firewalls)

The IANA maintains the official registry of assigned ports (http://www.iana.org/assignments/port-numbers).

Ah so it's not even just privileged ports. Handy link, thanks.

I'm designing an application with it's own protocol and I need to choose a port for it, what port should I choose (or how should I decide what port to set as default for it)?
just choose any port, as the product will cost everything, not the port :)