telnet.txt

C-Kermit源码。是使用串口/Modem和网络通讯的程序

                             WONT         WONT
              kermit    REQUESTED    REQUESTED    REQUESTED    REQUESTED
                             WONT         WONT
           forward-X      REFUSED     ACCEPTED      REFUSED      REFUSED
                             WONT         WONT

The second line listed for each option shows the currently negotiated state
of the option for the current connection.

The SET TELOPT command should be used instead of the older commands:

  SET TELNET AUTHENTICATION { ACCEPTED, REFUSED, REQUESTED, REQUIRED }
  SET TELNET BINARY-MODE    { ACCEPTED, REFUSED, REQUESTED, REQUIRED }
  SET TELNET ENCRYPTION     { ACCEPTED, REFUSED, REQUESTED, REQUIRED }
  SET TELNET ENVIRONMENT    { ON, OFF }
  SET TELNET NAWS           { ACCEPTED, REFUSED, REQUESTED, REQUIRED }
  SET TELNET XDISPLAY-LOC   { ACCEPTED, REFUSED, REQUESTED, REQUIRED }

which are now considered obsolete (but still supported).


4. TELNET COMMAND SUMMARY

TELNET /AUTH:<type> /ENCRYPT:<type> /USERID:<name> /PASSWORD:<string>
       <host> <port>
  The TELNET command is a shortcut for making interactive connections.
  It is the equivalent of specifying:

    SET TELOPT AUTH ...
    SET TELNET AUTH TYPE ...
    SET TELOPT ENCRYPT ...
    SET TELNET ENCRYPT TYPE ...
    SET LOGIN USERID ...
    SET LOGIN PASSWORD ...
    SET HOST /CONNECT <host> <port> /TELNET

  /AUTH:<type> is equivalent to SET TELNET AUTH TYPE <type> and
  SET TELOPT AUTH REQUIRED with the following exceptions.  If the type
  is AUTO, then SET TELOPT AUTH REQUESTED is executed and if the type
  is NONE, then SET TELOPT AUTH REFUSED is executed.

  /ENCRYPT:<type> is equivalent to SET TELNET ENCRYPT TYPE <type>
  and SET TELOPT ENCRYPT REQUIRED REQUIRED with the following exceptions.
  If the type is AUTO then SET TELOPT AUTH REQUESTED REQUESTED is executed
  and if the type is NONE then SET TELOPT ENCRYPT REFUSED REFUSED is
  executed.

  /USERID:[<name>]
  This switch is equivalent to SET LOGIN USERID <name> or SET TELNET
  ENVIRONMENT USER <name>.  If a string is given, it sent to host during
  Telnet negotiations; if this switch is given but the string is omitted, no
  user ID is sent to the host.  If this switch is not given, your current
  USERID value, \v(userid), is sent.  When a userid is sent to the host
  it is a request to login as the specified user.

  /PASSWORD:[<string>]
  This switch is equivalent to SET LOGIN PASSWORD.  If a string is given,
  it is treated as the password to be used (if required) by any Telnet
  Authentication protocol (Kerberos Ticket retrieval, Secure Remote
  Password, or X.509 certificate private key decryption.)  If no password
  switch is specified a prompt is issued to request the password if one
  is required for the negotiated authentication method.

For TCP/IP TELNET connections, which are in NVT (ASCII) mode by default:

SET LOGIN USERID <name>
  If a <name> is given, it sent to host during Telnet negotiations; if this
  switch is given but the string is omitted, no user ID is sent to the host.
  If this command is not given, your current USERID value, \v(userid), is
  sent.  When a userid is sent to the host it is a request to login as the
  specified user.

SET LOGIN PASSWORD <password>
  If a <password> is given, it is treated as the password to be used (if
  required) by any Telnet Authentication protocol (Kerberos Ticket retrieval,
  Secure Remote Password (SRP), or X.509 certificate private key decryption.)
  If no password is specified a prompt is issued to request the password if
  one is required for the negotiated authentication method.

SET TELNET AUTHENTICATION TYPE { AUTOMATIC, KERBEROS_IV, KERBEROS_V,
  NTLM, SSL, SRP, NONE } [ { ... } ... ]
  AUTOMATIC allows the host to choose the preferred type of authentication.
  Other values allow a specific authentication method to be used.  AUTOMATIC
  is the default.  Available options can vary depending on configuration;
  type SET TELNET AUTHENTICATION TYPE ? for a list.

  When the type is AUTOMATIC and Kermit is accepting incoming connections
  the supported authentication methods will be offered in the following
  order:

    NTLM (windows only)
    Kerberos 5
    Kerberos 4
    Secure Remote Password
    SSL

  This is the equivalent of the command:

    SET TELNET AUTH TYPE NTLM KRB5 KRB4 SRP SSL

SET TELNET AUTHENTICATION FORWARDING { ON, OFF }
  Set this to ON to forward Kerberos V ticket-granting-tickets to the host
  after authentication is complete.  OFF by default.

SET TELNET AUTHENTICATION ENCRYPT-FLAG { ANY, NONE, TELOPT }
  Use this command to specify which AUTH telopt encryption flags may be
  accepted in client mode or offered in server mode.  The default is ANY.

SET TELNET AUTHENTICATION HOW-FLAG { ANY, ONE-WAY, MUTUAL }
  Use this command to specify which AUTH telopt how flags may be
  accepted in client mode or offered in server mode.  The default is ANY.

SET TELNET BINARY-TRANSFER-MODE { ON, OFF }
  Set this command to ON if you want to force Kermit to negotiate 
  Telnet Binary in both directions when performing file transfers.  
  Default is OFF.  Alias SET TELNET BINARY-XFER-MODE.

SET TELNET BUG BINARY-ME-MEANS-U-TOO { ON, OFF }
  Set this to ON to try to overcome TELNET binary-mode misnegotiations by
  C-Kermit's TELNET partner.

SET TELNET BUG BINARY-U-MEANS-ME-TOO { ON, OFF }
  Set this to ON to try to overcome TELNET binary-mode misnegotiations by
  C-Kermit's TELNET partner.

SET TELNET BUG INFINITE-LOOP-CHECK { ON, OFF }
  Set this to ON to prevent Kermit from responding to a telnet negotiation
  sequence that enters an infinite loop.  The default is OFF because this
  should never occur.

SET TELNET BUG SB-IMPLIES-WILL-DO { ON, OFF }
  Set this to ON to allow Kermit to respond to telnet sub-negotiations if
  the peer forgets to respond to WILL with DO or to DO with WILL before
  sending a SB (subnegotiation).

SET TELNET DEBUG ON
  Displays all TELNET negotiations in full detail.

SET TELNET DELAY-SB { ON, OFF }
  When ON, telnet subnegotiation responses are delayed until after all
  authentication and encryption options are either successfully negotiated
  or refused.  This ensures that private data is protected.  When OFF, telnet
  subnegotiation responses are sent immediately.  The default is ON.

SET TELNET ECHO { LOCAL, REMOTE }
  C-Kermit's initial echoing state for TELNET connections, LOCAL by default.
  After the connection is made, TELNET negotiations determine the echoing.

SET TELNET ENCRYPTION TYPE { AUTOMATIC, CAST128_CFB64, CAST128_OFB64,
  CAST5_40_CFB64, CAST5_40_OFB64, DES_CFB64, DES_OFB64,
  DES3_CFB64, DES3_OFB64, NONE }
  AUTOMATIC allows the host to choose the preferred type of encryption.
  Other values allow a specific encryption method to be specified.
  AUTOMATIC is the default.  The list of options will vary depending
  on the encryption types selected at compilation time.

  When the type is AUTOMATIC and Kermit is accepting incoming connections
  the supported encryption methods will be offered in the following order:

    DES3_CFB64
    CAST128_CFB64
    DES_CFB64
    CAST5_40_CFB64
    DES3_OFB64
    CAST128_OFB64
    DES_OFB64
    CAST5_40_OFB64

SET TELNET ENVIRONMENT { variable-name [ value ] }
  This feature lets Kermit send the values of certain environment variables
  to the other computer if it asks for them.  The variable-name can be any
  of the "well-known" variables "USER", "JOB", "ACCT", "PRINTER",
  "SYSTEMTYPE", or "DISPLAY".  The default values are taken from your
  environment; use this command to change or remove them.

  The most commonly used variables and their default values are:

  USER:
    Telnet servers that request this value will use it as the name of the
    account to be accessed and will therefore not prompt you for a username.
    If a password is required to access the specified user's account only
    the password prompt will be issued.  The default value is the name of
    the user on the local machine.  This value may also be set with the
    command SET LOGIN USER <name>.

  DISPLAY:
    This variable is used to specify the location of the X Windows Server
    to be used by X Windows client applications executed on the remote host.
    This value is used by three telnet options: ENVIRONMENT, XDISPLOC, and
    FORWARD-X.  The default value is retrieved from the value of the DISPLAY
    environment variable in the local environment.

  PRINTER:
    This variable is used to specify the location of the LPR printer to be
    used for printing files on the host.  This variable is not set by
    default.

  SYSTEM:
    This variable is used to specify the operating system type of the local
    machine.  The default value is determined by Kermit.  Typical values
    are "UNIX", "VMS", "WIN32", and "OS2".

  See RFC1572 for further details.

SET TELNET LOCATION [ text ]
  Location string to send to the Telnet server if it asks.  By default this
  is picked up from the LOCATION environment variable.  Give this command
  with no text to disable this feature.

SET TELNET NEWLINE-MODE { NVT, BINARY-MODE } { OFF, ON, RAW }
  Determines how carriage returns are handled on TELNET connections.
  There are separate settings for NVT (ASCII) mode and binary mode.
  ON (default for NVT mode) means CRLF represents CR.
  OFF means CR followed by NUL represents CR.
  RAW (default for BINARY mode) means CR stands for itself.

SET TELNET PROMPT-FOR-USERID <prompt>
  Specifies a custom prompt to be used when prompting for a userid.
  Kermit will prompt for a userid if
    SET LOGIN USERID {}
  has been issued prior to a telnet authentication negotiation for
  an authentication type that requires the transmission of a name.
  (e.g. Secure Remote Password).

SET TELNET REMOTE-ECHO { ON, OFF }
  Applies only to incoming connections created with:
    SET HOST * <port> /TELNET
  This command determines whether Kermit will actually echo characters
  received from the remote when it has negotiated to do so.  The default
  is ON.  Remote echoing may be turned off when it is necessary to read
  a password with the INPUT command.

SET TELNET TERMINAL-TYPE name
  The terminal type to send to the remote TELNET host.  If none is given,
  your current SET TERMINAL TYPE value is sent, e.g. VT220.

SET TELNET TRANSFER-MODE { ON, OFF }
  When ON (OFF by default) and BINARY negotiations are not REFUSED Kermit
  will attempt to negotiate BINARY mode in each direction before the start
  of each file transfer.  After the transfer is complete BINARY mode will
  be restored to the pre-transfer state.

SET TELNET WAIT-FOR-NEGOTIATIONS { ON, OFF }
  Each Telnet option must be fully negotiated either On or Off before the
  session can continue.  This is especially true with options that require
  subnegotiations such as Authentication, Encryption, and Kermit; for
  proper support of these options Kermit must wait for the negotiations to
  complete.  Of course, Kermit has no way of knowing whether a reply is
  delayed or not coming at all, and so will wait forever before continuing
  the session.  If you know that Kermit's Telnet partner will not be sending
  the required replies, you should instruct Kermit to REFUSE specific
  options with the SET TELOPT command.  If you do not know which command
  the host is not responding to set this option of OFF.


5. DIAGNOSING AND FIXING PROBLEMS CONNECTING TO TELNET SERVERS

After we replaced the Telnet engine and added support for the new
functionality we found many Telnet servers that do not adhere to the Telnet
protocol as described in the IETF RFCs.  Here are some of the most common
bugs and the workarounds that Kermit provides the user to avoid them.

BUG: Telnet Server does not respond to telnet options.

Description:
  The telnet protocol requires that all initial requests for action (WILL or
  DO) must be responded to either in the affirmative (DO or WILL) or in the
  negative (DONT or WONT).  A negative response is required for all
  unrecognized options.  A failure to respond to a Telnet option may result
  in the peer waiting forever.

  This behavior is known to exist in the following telnet servers:

  AOS/VS II Release 2.20.00.39
  IBM OS/2 Warp 4.0 (all versions not configured with authentication modules)

Symptom:

  Kermit connects to the host, waits two minutes, and then reports a telnet
  protocol error followed by the list of outstanding negotiations.  Kermit
  has sent a Telnet option such as WILL AUTH and is waiting for the required
  response which never comes.  In C-Kermit you will see "Negotiations...."
  with many dots.  In K95 you will see the "spinner" twirl.

  Example:

  DNS Lookup...  Trying xxx.xxx.xxx.xxx...  Reverse DNS Lookup... (OK)
  Negotiations... ?Telnet Protocol Timeout
  ?Telnet waiting for response to WILL TERMINAL-TYPE
  ?Telnet waiting for response to WILL NAWS
  ?Telnet waiting for response to WILL AUTHENTICATION
  ?Telnet waiting for response to WILL NEW-ENVIRONMENT

  **** AOS/VS II  Release 2.20.00.39 / Press NEW-LINE to begin logging on ****

  Too slow - input timed out

Workaround:

  For each of the telnet options listed as missing a response issue a

    SET TELOPT <option> REFUSED [REFUSED]

  command.  For instance:

    SET TELOPT TERMINAL-TYPE REFUSED
    SET TELOPT NAWS REFUSED
    SET TELOPT AUTHENTICATION REFUSED
    SET TELOPT NEW-ENVIRONMENT REFUSED

BUG: Server sends a subnegotiation without negotiating the option

Description:
  The telnet protocol requires that subnegotiations not be sent until the
  peers have agreed to WILL or DO the specified option.  All subnegotiations
  received in a WONT or DONT state are to be ignored.

Symptom:
  There are two possibilities.  In the first, the host sends a subnegotiation
  such as

     IAC SB TERM_TYPE SEND IAC SE

  without Kermit attempting to use the telnet option.

     IAC WILL TERM_TYPE
     IAC DO TERM_TYPE

  In this case the subnegotiation request will be ignored and the
  subnegotiation response

     IAC SB TERM_TYPE IS <type> IAC SE

  will not be sent.  How this affects the sender of the illegal subnegotation
  is unknown.