specifying port numbers

Former Member

OK, heres a question that may or may not let me win a bet...

Is it possible to change the port used by a protocol? Any transmission protocal will be accepted, such as FTP, Telnet or PPTP.

Each of those mentioned uses a specifed port number, and i wanted to know if it was possible to alter that port, on any in use system (windows X, linux, (bah!)mac...etc).

Oh, not just whether its posible or not, but how to do it.

Can anyone help?

Thanks

Former Member

Re: specifying port numbers

Originally posted by cokephreak


Is it possible to change the port used by a protocol? Any transmission protocal will be accepted, such as FTP, Telnet or PPTP.

Each of those mentioned uses a specifed port number, and i wanted to know if it was possible to alter that port, on any in use system (windows X, linux, (bah!)mac...etc).

Oh, not just whether its posible or not, but how to do it.

Can anyone help?

Thanks

Yes it is possible with telnet ie:

telnet surfers.org 4242

For Unix systems anything below 1024 is for system use only not for users.

On a server to do this you'd use a script to redirect IO from a socket to another socket to circumvent firewall's supressing certain sockets.

http://www.oreilly.com/openbook/webclient/ch04.html

Former Member

Yes, it's possible, but the implementation would depend on what you are trying to achieve and on what platform. Since generally services depend on both client and server both would have to change.

Former Member

Yes it is possible with telnet ie:

telnet surfers.org 4242


Not that i want to seem ungrateful, but this is specifying what port you telnet to, but the local system is still using the sam eport for the outgoing connection.


For Unix systems anything below 1024 is for system use only not for users.
[b/]

not heard of this... if everything under 1024 is used for system, how come popmail use's 110?

Former Member

Originally posted by cokephreak

Not that i want to seem ungrateful, but this is specifying what port you telnet to, but the local system is still using the same port for the outgoing connection.

Um it's not. It shouldn't. Perhaps that's some special version of telnet you're using.

In which case use a port redirection script, and an understanding server, running it application on the same socket number or a similar redirection script to revert the client redirection.

if you're using Unix: edit /etc/services if it's going to be a permanent thing.
http://unixhelp.ed.ac.uk/CGI/man-cgi?services+5

cokephreak

not heard of this...

Yep has been so since 1971

cokephreak

if everything under 1024 is used for system, how come popmail use's 110?

Probably because it is setuid 0.
http://www.cs.unc.edu/~dewan/242/f97/notes/prot/node12.html