can we use well know ports for our own process ?

pradiptart · 08-06-2012, 02:10 AM

Hi,
I have written a shell script to scan the ports of system using nmap.

I am searching for some port number like 515 which is used by the Line Printer Daemon—print service and if it is there means I can say it is a printer as printer only have this daemon.

I don't know whether this port can be used by any other process.If yes kindly tell me about this whether it is possible to use the well known port or not by our own process.

If yes then I can't say it is a printer as port user is not a printer all the time.

Thnaks

Gleylancer · 08-06-2012, 05:13 AM

You can use any port for any service. An open port 515 does not mean there is a printer behind it. I can assign Apache to port 515. Or FTP, VNC, whatever, it's completely up to the administrator.

r0b0 · 08-08-2012, 07:50 AM

Technically, what Gleylancer said is true.
But there are standards for well-known ports and their usage. So, someone could technically have an FTP server listen on port 515 but it would be a non-standard (and, hence, wrong) thing to do.

pixellany · 08-08-2012, 07:56 AM

Quote:

So, someone could technically have an FTP server listen on port 515 but it would be a non-standard (and, hence, wrong) thing to do.

I disagree----doing non-standard things can help with security, and in so doing can be very much the right thing to do.

even ignoring security, non-standard is not inherently wrong. My whole Arch system is non-standard in many ways---and Arch has been in the "top ten" at distrowatch for some time now.

pan64 · 08-08-2012, 07:56 AM

yes, in general there are common standards, so when you want to use ftp, http, rsync, ssh or any other tool they will always assume the default port. But you can change it, you can use anything else. Using nonstandard ports or using these ports with nonstandard apps will/may confuse the users, and also will/may secure the system.