What protocol is used for remotely logging onto a computer

TELNET and FTP are Application Level Internet protocols. The TELNET and FTP protocol specifications have been implemented by many different sources, including The National Center for Supercomputer Applications (NCSA), and many other public domain and shareware sources.
The programs implementing the TELNET protocol are usually called telnet, but not always. Some notable exceptions are tn3270, WinQVT, and QWS3270, which are also TELNET protocol implementations. TELNET is used for remote login to other computers on the Internet.

The programs implementing the FTP protocol are usually called ftp, but there are exceptions to that too. A program called Fetch, distributed by Dartmouth College, WS_FTP, written and distributed by John Junod, and Ftptool, written by a Mike Sullivan, are FTP protocol implementations with graphic user interfaces. There's an enhanced FTP version, ncftp, that allows additional features, written by Mike Gleason. Also, FTP protocol implementations are often included in TELNET implementation programs, such as the ones distributed by NCSA. FTP is used for transferring files between computers on the Internet.

rlogin is a remote login service that was at one time exclusive to Berkeley 4.3 BSD UNIX. Essentially, it offers the same functionality as telnet, except that it passes to the remote computer information about the user's login environment. Machines can be configured to allow connections from trusted hosts without prompting for the users' passwords. A more secure version of this protocol is the Secure SHell, SSH, software written by Tatu Ylonen and available via ftp://ftp.net.ohio-state.edu/pub/security/ssh.

From a Unix prompt, these programs are invoked by typing the command (program name) and the (Internet) name of the remote machine to which to connect. You can also specify various options, as allowed, for these commands.

Syntax

telnet [options] [ remote_host [ port_number ] ]

tn3270 [options] [ remote_host [ port_number ] ]

ftp [options] [ remote_host ]

Common Options

ftp telnet Action

-d set debugging mode on

-d same as above (SVR4 only)

-i turn off interactive prompting

-n don't attempt auto-login on connection

-v verbose mode on

-l user connect with username, user, on the remote host (SVR4 only)

-8 8-bit data path (SVR4 only)

telnet and tn3270 allow you the option of specifying a port number to connect to on the remote host. For both commands it defaults to port number 23, the telnet port. Other ports are used for debugging of network services and for specialized resources.

Examples

telnet oscar.us.ohio-state.edu

tn3270 ohstmvsa.acs.ohio-state.edu

ftp magnus.acs.ohio-state.edu

The remote machine will query you for your login identification and your password. Machines set up as archives for software or information distribution often allow anonymous ftp connections. You ftp to the remote machine and login as anonymous (the login ftp is equivalent on many machines), that is, when asked for your "login" you would type anonymous.

Once you have successfully connected to a remote computer with telnet and rlogin (and assuming terminal emulation is appropriate) you will be able to use the machine as you always do.

Once you have successfully connected to a remote computer with ftp, you will be able to transfer a file "up" to that computer with the put command, or "down" from that computer with the get command. The syntax is as follows:

put local-file-name remote-file-name

get local-file-name remote-file-name

Other commands are available in ftp as well, depending on the specific "local" and "remote" FTP implementations. The help command will display a list of available commands. The help command will also display the purpose of a specific command. Examples of valid commands are shown below:

help display list of available commands

help mget display the purpose of the mget command ("get multiple files")

pwd present working directory

ls or dir directory list

cd change directory

lcd local change directory

open specify the machine you wish to connect with

user specify your login id (in cases where you are not prompted)

quit quit out of the FTP program