How to let an application use a low port number? (53)

[Dunhausen]

I want to use 53 for my torrent client so that I can avoid the campus firewall (it is the only port on the network that has no packet shaping).

I opened it in System->Administration->Firewall but I still get

terminate called after throwing an instance of 'asio::system_error'
what(): Permission denied

when I try to set it in my torrent program (deluge).


I know I could use netcat... but is there any way to let my client use that port without running another program?

[benjo]

Originally Posted by Dunhausen

I want to use 53 for my torrent client so that I can avoid the campus firewall (it is the only port on the network that has no packet shaping).

Can i just ask what's probably a really stoopid Q (i dont want to hijack your thread tho), but how did you manage to get this information? I would love to know what ports are open at my campus.

[markkuk]

Only programs running as root can open ports numbered <1024. Additionally, you probably must change SELinux settings to allow deluge to use the port reserved for BIND.

[Iron_Mike]

How are you going to use use port 53 when they are tagged for DNS lookups????

[Dunhausen]

Originally Posted by benjo

Can i just ask what's probably a really stoopid Q (i dont want to hijack your thread tho), but how did you manage to get this information? I would love to know what ports are open at my campus.

I found out by word of mouth, but you should be able to use nmap. Invoke it only with the paranoid timing policy, though.

Originally Posted by markkuk

Only programs running as root can open ports numbered <1024. Additionally, you probably must change SELinux settings to allow deluge to use the port reserved for BIND.

Ah, thank you. SELinux is disabled; I had thought that might be the case for the low-numbered ports but then the program also crashes when run as root. Isn't there some way to give a program root privileges but still let regular users invoke it? Perhaps I can trick the program into starting by using sudo. (yes, I am very security conscious )

Originally Posted by Iron_Mike

How are you going to use use port 53 when they are tagged for DNS lookups????

Port numbers are only convention, yes? I have set up port forwarding to remote servers using other silly ports before. This is a bit trickier, though, or seems to be.

On Windows it is no big deal to use the low numbered ports since windows doesn't care about security, and on that having utorrent run on 53 works great... I get line-speed for the downloads.

[Iron_Mike]

Try any other ports greater than port 1024 and go from there.....But if you're trying to mask p2p or some other file sharing, good luck......