[robespierre]

/etc/services doesn't "turn on" anything, it is simply a list. You have it confused with inetd.conf.

ssh has X11 forwarding, which may be what was called "tunneling". This sets the DISPLAY environment variable to point to the ssh connection, so that typing "xterm" in a ssh session will open a window on your screen instead of on the remote computer. It is set up with a config file, see "man ssh_config".

There are a lot of limitations of X11 forwarding because of its security concerns, and because the SGI uses GL or OpenGL for its interface instead of vanilla X11.

There is a more basic ssh feature called the control port, which lets you share multiple activities (such as file copies and shells) over a single ssh connection. See "ControlPath" in "man ssh_config".

The port forwarding commands like -L, -R, or -D are for passing Internet sockets over the ssh connection. This is only useful when you want to make it look like your Internet traffic is originating from the ssh server (in other words, there is no point using them on a local network).

Telnet doesn't do any of this stuff (but ironically, Kerberized Telnet does do encryption, so there is nothing that restricts it to local networks).

For more convenient text-mode work on a remote computer, you could also use screen or tmux.