telnetd

telnet protocol server

sudo /usr/sbin/in.telnetd [-hnNs] [-a authmode] [-D debugmode] 
[-L loginprg] [-S tos] [-X authtype] [-edebug] [-debug port]

Server which supports the telnet interactive communication protocol.

Normally invoked by the internet server inetd for requests to connect to the telnet port (22) as defined in /etc/services

-a authmode

mode to be used for authentication (before login) is invoked.

`debug`	Turns on authentication debugging
`user`	Only allow connections when the remote user can provide valid authentication information to identify the user, and is allowed access to the specified account without providing a password.
`valid`	Only allow connections when the remote user can provide valid authentication information to identify the user. `login` performs user verification needed if the remote user is not allowed automatic access
`other`	Only allow connections that supply some authentication information.
`none`	default . Authentication information is not required. If no or insufficient authentication information is provided, login provides the necessary user verification.
`off`	disables the authentication code. All user verification will happen through the login(1) program.

-D debugmode

output debugging information to the connection. Repeated use arranges composite debug reports.

`options`	information about the negotiation of telnet options.
`report`	`options` information, plus additional information about processing
`netdata`	Displays the data stream received
`ptydata`	Displays data written to the pty.
`exercise`

-edebug enable encryption debugging

-h Disables the printing of host-specific information before login has been completed.

-L loginprg login program. default, /usr/lib/telnetlogin

-n Disable TCP keep-alives.
Normally probe idle connections to determine if the client is still there, allowing clean for those that are not.

-N Disable reverse DNS lookups and use the numeric IP address in logs and $REMOTEHOST.

-s support for SecurID cards, passed to login, for controlling remote logins from outside of a firewall.

-S tos Sets the IP type-of-service (TOS)

-X authtype disables the use of authtype authentication, and disable a specific authentication type

/etc/issue.net is displayed before the login prompt of a telnet session (see issue.net(5)).

Operates by allocating a pseudo-terminal device (see pty(4)) , then creating a login process which has the slave side as stdin, stdout, and stderr.

When a telnet session is started , telnetd sends the client supported options.

 
           DO AUTHENTICATION
           WILL ENCRYPT
           DO TERMINAL TYPE
           DO TSPEED
           DO XDISPLOC
           DO NEW-ENVIRON
           WILL SUPPRESS GO AHEAD
           DO ECHO
           DO LINEMODE
           DO NAWS
           WILL STATUS
           DO LFLOW
           DO TIMING-MARK

The pseudo-terminal operates in "cooked" mode, and with XTABS CRMOD enabled (see tty(4)).

telnet options:

`WILL ECHO`	With `LINEMODE` `WILL/WONT ECHO` sent to the client to indicate the current state of terminal echoing. When terminal echo is not desired, `WILL ECHO` is sent to indicate that telnetd will do echoing any data that needs to be echoed , and then nothing is echoed. When terminal echo is desired, `WONT ECHO` is sent to indicate that telnetd will not do echoing, so the client should do any terminal echoing that is needed.
`WILL BINARY`	client is willing to send a 8 bits of data, rather than the normal 7 bits
`WILL SGA`	will not send IAC GA, go ahead
`WILL STATUS`	will send the client, status of TELNET options.
`WILL TIMING-MARK`	When `DO TIMING-MARK` command is received, it is responded with `WILL TIMING-MARK`
`WILL LOGOUT`	When `DO LOGOUT` is received, a `WILL LOGOUT` is sent and the session is shut down.
`WILL ENCRYPT`	will decrypt the data stream.

Telnetd has support for enabling remotely the following TELNET options:

`DO BINARY`	Sent to indicate that telnetd is willing to receive an 8 bit data stream.
`DO LFLOW`	client should handle flow control characters remotely.
`DO TERMINAL-TYPE`	able to request the name of the type of terminal
`DO SGA`	does not need to receive IAC GA, the go ahead command.
`DO NAWS`	Notify adjust window sise. client should inform the server when the window size changes.
`DO TERMINAL-SPEED`	request information about the speed of the serial line
`DO XDISPLOC`	request the name of the X windows display that is associated
`DO NEW-ENVIRON`	request environment variable information, (see RFC 1572.)
`DO LINEMODE`	client should do line by line processing.
`DO TIMING-MARK`	the client responded with `WONT LINEMODE`. If the client responds with `WILL TM`, the it is assumed that the client supports kludge linemode. `-k` disables this.
`DO AUTHENTICATION`	will receive authentication information for automatic login.
`DO ENCRYPT`	will decrypt the data stream. issue.net(5)).

FILES

/etc/services,
/etc/issue.net SEE ALSO telnet(1), login(1), issue.net(5), STANDARDS

     RFC-854   PROTOCOL 
     RFC-855   OPTION 
     RFC-856   BINARY TRANSMISSION
     RFC-857   ECHO 
     RFC-858   SUPPRESS GO AHEAD 
     RFC-859   STATUS 
     RFC-860   TIMING MARK 
     RFC-861   EXTENDED - LIST 
     RFC-885   END OF RECORD 
     RFC-1073  Window Size 
     RFC-1079  Terminal Speed 
     RFC-1091  Terminal-Type

     RFC-1096  X Display Location 
     RFC-1123  Requirements for Internet Hosts -- Application and Support
     RFC-1184  Linemode 
     RFC-1372  Remote Flow Control 
     RFC-1416  AuthenticationOption
     RFC-1411  Authentication: Kerberos Version 4
     RFC-1412  Authentication: SPX
     RFC-1571  Environment Option Interoperability Issues
     RFC-1572  Environment