[Docs] [txt|pdf] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 RFC 4254

Network Working Group                                          T. Ylonen
Internet-Draft                                                T. Kivinen
Expires: January 18, 2002               SSH Communications Security Corp
                                                             M. Saarinen
                                                 University of Jyvaskyla
                                                                T. Rinne
                                                             S. Lehtinen
                                        SSH Communications Security Corp
                                                           July 20, 2001


                        SSH Connection Protocol
                    draft-ietf-secsh-connect-11.txt

Status of this Memo

      This document is an Internet-Draft and is in full conformance with
      all provisions of Section 10 of RFC2026.

      Internet-Drafts are working documents of the Internet Engineering
      Task Force (IETF), its areas, and its working groups.  Note that
      other groups may also distribute working documents as Internet-
      Drafts.

      Internet-Drafts are draft documents valid for a maximum of six
      months and may be updated, replaced, or obsoleted by other
      documents at any time.  It is inappropriate to use Internet-Drafts
      as reference material or to cite them other than as "work in
      progress."

      The list of current Internet-Drafts can be accessed at
      http://www.ietf.org/ietf/1id-abstracts.txt.

      The list of Internet-Draft Shadow Directories can be accessed at
      http://www.ietf.org/shadow.html.

      This Internet-Draft will expire on January 18, 2002.

Copyright Notice

      Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

      SSH is a protocol for secure remote login and other secure network
      services over an insecure network.

      This document describes the SSH Connection Protocol.  It provides
      interactive login sessions, remote execution of commands,



Ylonen, et. al.         Expires January 18, 2002                [Page 1]

Internet-Draft           SSH Connection Protocol               July 2001


      forwarded TCP/IP connections, and forwarded X11 connections.  All
      of these channels are multiplexed into a single encrypted tunnel.

      The SSH Connection Protocol has been designed to run on top of the
      SSH transport layer and user authentication protocols.

Table of Contents

   1.    Introduction . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.    Global Requests  . . . . . . . . . . . . . . . . . . . . . .  3
   3.    Channel Mechanism  . . . . . . . . . . . . . . . . . . . . .  3
   3.1   Opening a Channel  . . . . . . . . . . . . . . . . . . . . .  4
   3.2   Data Transfer  . . . . . . . . . . . . . . . . . . . . . . .  5
   3.3   Closing a Channel  . . . . . . . . . . . . . . . . . . . . .  6
   3.4   Channel-Specific Requests  . . . . . . . . . . . . . . . . .  7
   4.    Interactive Sessions . . . . . . . . . . . . . . . . . . . .  7
   4.1   Opening a Session  . . . . . . . . . . . . . . . . . . . . .  8
   4.2   Requesting a Pseudo-Terminal . . . . . . . . . . . . . . . .  8
   4.3   X11 Forwarding . . . . . . . . . . . . . . . . . . . . . . .  8
   4.3.1 >Requesting X11 Forwarding . . . . . . . . . . . . . . . . .  8
   4.3.2 >X11 Channels  . . . . . . . . . . . . . . . . . . . . . . .  9
   4.4   Environment Variable Passing . . . . . . . . . . . . . . . .  9
   4.5   Starting a Shell or a Command  . . . . . . . . . . . . . . . 10
   4.6   Session Data Transfer  . . . . . . . . . . . . . . . . . . . 11
   4.7   Window Dimension Change Message  . . . . . . . . . . . . . . 11
   4.8   Local Flow Control . . . . . . . . . . . . . . . . . . . . . 11
   4.9   Signals  . . . . . . . . . . . . . . . . . . . . . . . . . . 12
   4.10  Returning Exit Status  . . . . . . . . . . . . . . . . . . . 12
   5.    TCP/IP Port Forwarding . . . . . . . . . . . . . . . . . . . 13
   5.1   Requesting Port Forwarding . . . . . . . . . . . . . . . . . 14
   5.2   TCP/IP Forwarding Channels . . . . . . . . . . . . . . . . . 14
   6.    Encoding of Terminal Modes . . . . . . . . . . . . . . . . . 15
   7.    Summary of Message Numbers . . . . . . . . . . . . . . . . . 17
   8.    Security Considerations  . . . . . . . . . . . . . . . . . . 18
   9.    Trademark Issues . . . . . . . . . . . . . . . . . . . . . . 18
   10.   Additional Information . . . . . . . . . . . . . . . . . . . 19
         References . . . . . . . . . . . . . . . . . . . . . . . . . 19
         Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 20
         Full Copyright Statement . . . . . . . . . . . . . . . . . . 21












Ylonen, et. al.         Expires January 18, 2002                [Page 2]

Internet-Draft           SSH Connection Protocol               July 2001


   1. Introduction

      The SSH Connection Protocol has been designed to run on top of the
      SSH transport layer and user authentication protocols.  It
      provides interactive login sessions, remote execution of commands,
      forwarded TCP/IP connections, and forwarded X11 connections.  The
      service name for this protocol (after user authentication) is
      "ssh-connection".

      This document should be read only after reading the SSH
      architecture document [SSH-ARCH].  This document freely uses
      terminology and notation from the architecture document without
      reference or further explanation.

   2. Global Requests

      There are several kinds of requests that affect the state of the
      remote end "globally", independent of any channels.  An example is
      a request to start TCP/IP forwarding for a specific port.  All
      such requests use the following format.

     byte      SSH_MSG_GLOBAL_REQUEST
     string    request name (restricted to US-ASCII)
     boolean   want reply
     ... request-specific data follows

      The recipient will respond to this message with
      SSH_MSG_REQUEST_SUCCESS, SSH_MSG_REQUEST_FAILURE, or some request-
      specific continuation messages if `want reply' is TRUE.

     byte      SSH_MSG_REQUEST_SUCCESS

      If the recipient does not recognize or support the request, it
      simply responds with SSH_MSG_REQUEST_FAILURE.

     byte      SSH_MSG_REQUEST_FAILURE


   3. Channel Mechanism

      All terminal sessions, forwarded connections, etc.  are channels.
      Either side may open a channel.  Multiple channels are multiplexed
      into a single connection.

      Channels are identified by numbers at each end.  The number
      referring to a channel may be different on each side.  Requests to
      open a channel contain the sender's channel number.  Any other
      channel-related messages contain the recipient's channel number



Ylonen, et. al.         Expires January 18, 2002                [Page 3]

Internet-Draft           SSH Connection Protocol               July 2001


      for the channel.

      Channels are flow-controlled.  No data may be sent to a channel
      until a message is received to indicate that window space is
      available.

   3.1 Opening a Channel

      When either side wishes to open a new channel, it allocates a
      local number for the channel.  It then sends the following message
      to the other side, and includes the local channel number and
      initial window size in the message.

     byte      SSH_MSG_CHANNEL_OPEN
     string    channel type (restricted to US-ASCII)
     uint32    sender channel
     uint32    initial window size
     uint32    maximum packet size
     ... channel type specific data follows

      The channel type is a name as described in the SSH architecture
      document, with similar extension mechanisms.  `sender channel' is
      a local identifier for the channel used by the sender of this
      message.  `initial window size' specifies how many bytes of
      channel data can be sent to the sender of this message without
      adjusting the window.  `Maximum packet size' specifies the maximum
      size of an individual data packet that can be sent to the sender
      (for example, one might want to use smaller packets for
      interactive connections to get better interactive response on slow
      links).

      The remote side then decides whether it can open the channel, and
      responds with either

     byte      SSH_MSG_CHANNEL_OPEN_CONFIRMATION
     uint32    recipient channel
     uint32    sender channel
     uint32    initial window size
     uint32    maximum packet size
     ... channel type specific data follows

      where `recipient channel' is the channel number given in the
      original open request, and `sender channel' is the channel number
      allocated by the other side, or

     byte      SSH_MSG_CHANNEL_OPEN_FAILURE
     uint32    recipient channel
     uint32    reason code



Ylonen, et. al.         Expires January 18, 2002                [Page 4]

Internet-Draft           SSH Connection Protocol               July 2001


     string    additional textual information (ISO-10646 UTF-8 [RFC2279])
     string    language tag (as defined in [RFC1766])

      If the recipient of the SSH_MSG_CHANNEL_OPEN message does not
      support the specified channel type, it simply responds with
      SSH_MSG_CHANNEL_OPEN_FAILURE.  The client MAY show the additional
      information to the user.  If this is done, the client software
      should take the precautions discussed in [SSH-ARCH].

      The following reason codes are defined:

     #define SSH_OPEN_ADMINISTRATIVELY_PROHIBITED    1
     #define SSH_OPEN_CONNECT_FAILED                 2
     #define SSH_OPEN_UNKNOWN_CHANNEL_TYPE           3
     #define SSH_OPEN_RESOURCE_SHORTAGE              4


   3.2 Data Transfer

      The window size specifies how many bytes the other party can send
      before it must wait for the window to be adjusted.  Both parties
      use the following message to adjust the window.

     byte      SSH_MSG_CHANNEL_WINDOW_ADJUST
     uint32    recipient channel
     uint32    bytes to add

      After receiving this message, the recipient MAY send the given
      number of bytes more than it was previously allowed to send; the
      window size is incremented.

      Data transfer is done with messages of the following type.

     byte      SSH_MSG_CHANNEL_DATA
     uint32    recipient channel
     string    data

      The maximum amount of data allowed is the current window size.
      The window size is decremented by the amount of data sent.  Both
      parties MAY ignore all extra data sent after the allowed window is
      empty.

      Additionally, some channels can transfer several types of data.
      An example of this is stderr data from interactive sessions.  Such
      data can be passed with SSH_MSG_CHANNEL_EXTENDED_DATA messages,
      where a separate integer specifies the type of the data.  The
      available types and their interpretation depend on the type of the
      channel.



Ylonen, et. al.         Expires January 18, 2002                [Page 5]

Internet-Draft           SSH Connection Protocol               July 2001


     byte      SSH_MSG_CHANNEL_EXTENDED_DATA
     uint32    recipient_channel
     uint32    data_type_code
     string    data

      Data sent with these messages consumes the same window as ordinary
      data.

      Currently, only the following type is defined.

   #define SSH_EXTENDED_DATA_STDERR                1


   3.3 Closing a Channel

      When a party will no longer send more data to a channel, it SHOULD
      send SSH_MSG_CHANNEL_EOF.

     byte      SSH_MSG_CHANNEL_EOF
     uint32    recipient_channel

      No explicit response is sent to this message; however, the
      application may send EOF to whatever is at the other end of the
      channel.  Note that the channel remains open after this message,
      and more data may still be sent in the other direction.  This
      message does not consume window space and can be sent even if no
      window space is available.

      When either party wishes to terminate the channel, it sends
      SSH_MSG_CHANNEL_CLOSE.  Upon receiving this message, a party MUST
      send back a SSH_MSG_CHANNEL_CLOSE unless it has already sent this
      message for the channel.  The channel is considered closed for a
      party when it has both sent and received SSH_MSG_CHANNEL_CLOSE,
      and the party may then reuse the channel number.  A party MAY send
      SSH_MSG_CHANNEL_CLOSE without having sent or received
      SSH_MSG_CHANNEL_EOF.

     byte      SSH_MSG_CHANNEL_CLOSE
     uint32    recipient_channel

      This message does not consume window space and can be sent even if
      no window space is available.

      It is recommended that any data sent before this message is
      delivered to the actual destination, if possible.






Ylonen, et. al.         Expires January 18, 2002                [Page 6]

Internet-Draft           SSH Connection Protocol               July 2001


   3.4 Channel-Specific Requests

      Many channel types have extensions that are specific to that
      particular channel type.  An example is requesting a pty (pseudo
      terminal) for an interactive session.

      All channel-specific requests use the following format.

     byte      SSH_MSG_CHANNEL_REQUEST
     uint32    recipient channel
     string    request type (restricted to US-ASCII)
     boolean   want reply
     ... type-specific data

      If want reply is FALSE, no response will be sent to the request.
      Otherwise, the recipient responds with either
      SSH_MSG_CHANNEL_SUCCESS or SSH_MSG_CHANNEL_FAILURE, or request-
      specific continuation messages.  If the request is not recognized
      or is not supported for the channel, SSH_MSG_CHANNEL_FAILURE is
      returned.

      This message does not consume window space and can be sent even if
      no window space is available.  Request types are local to each
      channel type.

      The client is allowed to send further messages without waiting for
      the response to the request.

     byte      SSH_MSG_CHANNEL_SUCCESS
     uint32    recipient_channel


     byte      SSH_MSG_CHANNEL_FAILURE
     uint32    recipient_channel

      These messages do not consume window space and can be sent even if
      no window space is available.

   4. Interactive Sessions

      A session is a remote execution of a program.  The program may be
      a shell, an application, a system command, or some built-in
      subsystem.  It may or may not have a tty, and may or may not
      involve X11 forwarding.  Multiple sessions can be active
      simultaneously.






Ylonen, et. al.         Expires January 18, 2002                [Page 7]

Internet-Draft           SSH Connection Protocol               July 2001


   4.1 Opening a Session

      A session is started by sending the following message.

     byte      SSH_MSG_CHANNEL_OPEN
     string    "session"
     uint32    sender channel
     uint32    initial window size
     uint32    maximum packet size

      Client implementations SHOULD reject any session channel open
      requests to make it more difficult for a corrupt server to attack
      the client.

   4.2 Requesting a Pseudo-Terminal

      A pseudo-terminal can be allocated for the session by sending the
      following message.

     byte      SSH_MSG_CHANNEL_REQUEST
     uint32    recipient_channel
     string    "pty-req"
     boolean   want_reply
     string    TERM environment variable value (e.g., vt100)
     uint32    terminal width, characters (e.g., 80)
     uint32    terminal height, rows (e.g., 24)
     uint32    terminal width, pixels (e.g., 640)
     uint32    terminal height, pixels (e.g., 480)
     string    encoded terminal modes

      The encoding of terminal modes is described in Section Encoding of
      Terminal Modes (Section 6).  Zero dimension parameters MUST be
      ignored.  The character/row dimensions override the pixel
      dimensions (when nonzero).  Pixel dimensions refer to the drawable
      area of the window.

      The dimension parameters are only informational.

      The client SHOULD ignore pty requests.

   4.3 X11 Forwarding

   4.3.1 >Requesting X11 Forwarding

      X11 forwarding may be requested for a session by sending

     byte      SSH_MSG_CHANNEL_REQUEST
     uint32    recipient channel



Ylonen, et. al.         Expires January 18, 2002                [Page 8]

Internet-Draft           SSH Connection Protocol               July 2001


     string    "x11-req"
     boolean   want reply
     boolean   single connection
     string    x11 authentication protocol
     string    x11 authentication cookie
     uint32    x11 screen number

      It is recommended that the authentication cookie that is sent be a
      fake, random cookie, and that the cookie is checked and replaced
      by the real cookie when a connection request is received.

      X11 connection forwarding should stop when the session channel is
      closed; however, already opened forwardings should not be
      automatically closed when the session channel is closed.

      If `single connection' is TRUE, only a single connection should be
      forwarded.  No more connections will be forwarded after the first,
      or after the session channel has been closed.

      The `x11 authentication protocol' is the name of the X11
      authentication method used, e.g.  "MIT-MAGIC-COOKIE-1".

      X Protocol is documented in [SCHEIFLER].

   4.3.2 >X11 Channels

      X11 channels are opened with a channel open request.  The
      resulting channels are independent of the session, and closing the
      session channel does not close the forwarded X11 channels.

     byte      SSH_MSG_CHANNEL_OPEN
     string    "x11"
     uint32    sender channel
     uint32    initial window size
     uint32    maximum packet size
     string    originator address (e.g. "192.168.7.38")
     uint32    originator port

      The recipient should respond with
      SSH_MSG_CHANNEL_OPEN_CONFIRMATION or SSH_MSG_CHANNEL_OPEN_FAILURE.

      Implementations MUST reject any X11 channel open requests if they
      have not requested X11 forwarding.

   4.4 Environment Variable Passing

      Environment variables may be passed to the shell/command to be
      started later.  Typically, each machine will have a preconfigured



Ylonen, et. al.         Expires January 18, 2002                [Page 9]

Internet-Draft           SSH Connection Protocol               July 2001


      set of variables that it will allow.  Since uncontrolled setting
      of environment variables can be very dangerous, it is recommended
      that implementations allow setting only variables whose names have
      been explicitly configured to be allowed.

     byte      SSH_MSG_CHANNEL_REQUEST
     uint32    recipient channel
     string    "env"
     boolean   want reply
     string    variable name
     string    variable value


   4.5 Starting a Shell or a Command

      Once the session has been set up, a program is started at the
      remote end.  The program can be a shell, an application program or
      a subsystem with a host-independent name.  Only one of these
      requests can succeed per channel.

     byte      SSH_MSG_CHANNEL_REQUEST
     uint32    recipient channel
     string    "shell"
     boolean   want reply

      This message will request the user's default shell (typically
      defined in /etc/passwd in UNIX systems) to be started at the other
      end.

     byte      SSH_MSG_CHANNEL_REQUEST
     uint32    recipient channel
     string    "exec"
     boolean   want reply
     string    command

      This message will request the server to start the execution of the
      given command.  The command string may contain a path.  Normal
      precautions MUST be taken to prevent the execution of unauthorized
      commands.

     byte      SSH_MSG_CHANNEL_REQUEST
     uint32    recipient channel
     string    "subsystem"
     boolean   want reply
     string    subsystem name

      This last form executes a predefined subsystem.  It is expected
      that these will include a general file transfer mechanism, and



Ylonen, et. al.         Expires January 18, 2002               [Page 10]

Internet-Draft           SSH Connection Protocol               July 2001


      possibly other features.  Implementations may also allow
      configuring more such mechanisms.  As the user's shell is usually
      used to execute the subsystem, it is advisable for the subsystem
      protocol to have a "magic cookie" at the beginning of the protocol
      transaction to distinguish from arbitrary output from shell
      initialization scripts etc.  This spurious output from the shell
      may be filtered out either at the server or at the client.

      The server SHOULD not halt the execution of the protocol stack
      when starting a shell or a program.  All input and output from
      these SHOULD be redirected to the channel or to the encrypted
      tunnel.

      It is RECOMMENDED to request and check the reply for these
      messages.  The client SHOULD ignore these messages.

   4.6 Session Data Transfer

      Data transfer for a session is done using SSH_MSG_CHANNEL_DATA and
      SSH_MSG_CHANNEL_EXTENDED_DATA packets and the window mechanism.
      The extended data type SSH_EXTENDED_DATA_STDERR has been defined
      for stderr data.

   4.7 Window Dimension Change Message

      When the window (terminal) size changes on the client side, it MAY
      send a message to the other side to inform it of the new
      dimensions.

     byte      SSH_MSG_CHANNEL_REQUEST
     uint32    recipient_channel
     string    "window-change"
     boolean   FALSE
     uint32    terminal width, columns
     uint32    terminal height, rows
     uint32    terminal width, pixels
     uint32    terminal height, pixels

       No response SHOULD be sent to this message.

   4.8 Local Flow Control

      On many systems, it is possible to determine if a pseudo-terminal
      is using control-S/control-Q flow control.  When flow control is
      allowed, it is often desirable to do the flow control at the
      client end to speed up responses to user requests.  This is
      facilitated by the following notification.  Initially, the server
      is responsible for flow control.  (Here, again, client means the



Ylonen, et. al.         Expires January 18, 2002               [Page 11]

Internet-Draft           SSH Connection Protocol               July 2001


      side originating the session, and server means the other side.)

      The message below is used by the server to inform the client when
      it can or cannot perform flow control (control-S/control-Q
      processing).  If `client can do' is TRUE, the client is allowed to
      do flow control using control-S and control-Q.  The client MAY
      ignore this message.

     byte      SSH_MSG_CHANNEL_REQUEST
     uint32    recipient channel
     string    "xon-xoff"
     boolean   FALSE
     boolean   client can do

      No response is sent to this message.

   4.9 Signals

      A signal can be delivered to the remote process/service using the
      following message.  Some systems may not implement signals, in
      which case they SHOULD ignore this message.

     byte      SSH_MSG_CHANNEL_REQUEST
     uint32    recipient channel
     string    "signal"
     boolean   FALSE
     string    signal name without the "SIG" prefix.

      Signal names will be encoded as discussed in the "exit-signal"
      SSH_MSG_CHANNEL_REQUEST.

   4.10 Returning Exit Status

      When the command running at the other end terminates, the
      following message can be sent to return the exit status of the
      command.  Returning the status is RECOMMENDED.  No acknowledgment
      is sent for this message.  The channel needs to be closed with
      SSH_MSG_CHANNEL_CLOSE after this message.

      The client MAY ignore these messages.

     byte      SSH_MSG_CHANNEL_REQUEST
     uint32    recipient_channel
     string    "exit-status"
     boolean   FALSE
     uint32    exit_status

      The remote command may also terminate violently due to a signal.



Ylonen, et. al.         Expires January 18, 2002               [Page 12]

Internet-Draft           SSH Connection Protocol               July 2001


      Such a condition can be indicated by the following message.  A
      zero exit_status usually means that the command terminated
      successfully.

     byte      SSH_MSG_CHANNEL_REQUEST
     uint32    recipient channel
     string    "exit-signal"
     boolean   FALSE
     string    signal name without the "SIG" prefix.
     boolean   core dumped
     string    error message (ISO-10646 UTF-8)
     string    language tag (as defined in [RFC1766])

      The signal name is one of the following (these are from [POSIX])

     ABRT
     ALRM
     FPE
     HUP
     ILL
     INT
     KILL
     PIPE
     QUIT
     SEGV
     TERM
     USR1
     USR2

      Additional signal names MAY be sent in the format "sig-name@xyz",
      where `sig-name' and `xyz' may be anything a particular
      implementor wants (except the `@' sign).  However, it is suggested
      that if a `configure' script is used, the non-standard signal
      names it finds be encoded as "SIG@xyz.config.guess", where `SIG'
      is the signal name without the "SIG" prefix, and `xyz' be the host
      type, as determined by `config.guess'.

      The `error message' contains an additional explanation of the
      error message.  The message may consist of multiple lines.  The
      client software MAY display this message to the user.  If this is
      done, the client software should take the precautions discussed in
      [SSH-ARCH].

   5. TCP/IP Port Forwarding







Ylonen, et. al.         Expires January 18, 2002               [Page 13]

Internet-Draft           SSH Connection Protocol               July 2001


   5.1 Requesting Port Forwarding

      A party need not explicitly request forwardings from its own end
      to the other direction.  However, if it wishes that connections to
      a port on the other side be forwarded to the local side, it must
      explicitly request this.

     byte      SSH_MSG_GLOBAL_REQUEST
     string    "tcpip-forward"
     boolean   want reply
     string    address to bind (e.g. "0.0.0.0")
     uint32    port number to bind

      `Address to bind' and `port number to bind' specify the IP address
      and port to which the socket to be listened is bound.  The address
      should be "0.0.0.0" if connections are allowed from anywhere.
      (Note that the client can still filter connections based on
      information passed in the open request.)

      Implementations should only allow forwarding privileged ports if
      the user has been authenticated as a privileged user.

      Client implementations SHOULD reject these messages; they are
      normally only sent by the client.

      A port forwarding can be cancelled with the following message.
      Note that channel open requests may be received until a reply to
      this message is received.

     byte      SSH_MSG_GLOBAL_REQUEST
     string    "cancel-tcpip-forward"
     boolean   want reply
     string    address_to_bind (e.g. "127.0.0.1")
     uint32    port number to bind

      Client implementations SHOULD reject these messages; they are
      normally only sent by the client.

   5.2 TCP/IP Forwarding Channels

      When a connection comes to a port for which remote forwarding has
      been requested, a channel is opened to forward the port to the
      other side.

     byte      SSH_MSG_CHANNEL_OPEN
     string    "forwarded-tcpip"
     uint32    sender channel
     uint32    initial window size



Ylonen, et. al.         Expires January 18, 2002               [Page 14]

Internet-Draft           SSH Connection Protocol               July 2001


     uint32    maximum packet size
     string    address that was connected
     uint32    port that was connected
     string    originator IP address
     uint32    originator port

      Implementations MUST reject these messages unless they have
      previously requested a remote TCP/IP port forwarding with the
      given port number.

      When a connection comes to a locally forwarded TCP/IP port, the
      following packet is sent to the other side.  Note that these
      messages MAY be sent also for ports for which no forwarding has
      been explicitly requested.  The receiving side must decide whether
      to allow the forwarding.

     byte      SSH_MSG_CHANNEL_OPEN
     string    "direct-tcpip"
     uint32    sender channel
     uint32    initial window size
     uint32    maximum packet size
     string    host to connect
     uint32    port to connect
     string    originator IP address
     uint32    originator port

      `Host to connect' and `port to connect' specify the TCP/IP host
      and port where the recipient should connect the channel.  `Host to
      connect' may be either a domain name or a numeric IP address.

      `Originator IP address' is the numeric IP address of the machine
      where the connection request comes from, and `originator port' is
      the port on the originator host from where the connection came
      from.

      Forwarded TCP/IP channels are independent of any sessions, and
      closing a session channel does not in any way imply that forwarded
      connections should be closed.

      Client implementations SHOULD reject direct TCP/IP open requests
      for security reasons.

   6. Encoding of Terminal Modes

      Terminal modes (as passed in a pty request) are encoded into a
      byte stream.  It is intended that the coding be portable across
      different environments.




Ylonen, et. al.         Expires January 18, 2002               [Page 15]

Internet-Draft           SSH Connection Protocol               July 2001


      The tty mode description is a stream of bytes.  The stream
      consists of opcode-argument pairs.  It is terminated by opcode
      TTY_OP_END (0).  Opcodes 1 to 159 have a single uint32 argument.
      Opcodes 160 to 255 are not yet defined, and cause parsing to stop
      (they should only be used after any other data).

      The client SHOULD put in the stream any modes it knows about, and
      the server MAY ignore any modes it does not know about.  This
      allows some degree of machine-independence, at least between
      systems that use a POSIX-like tty interface.  The protocol can
      support other systems as well, but the client may need to fill
      reasonable values for a number of parameters so the server pty
      gets set to a reasonable mode (the server leaves all unspecified
      mode bits in their default values, and only some combinations make
      sense).

      The following opcodes have been defined.  The naming of opcodes
      mostly follows the POSIX terminal mode flags.

   0   TTY_OP_END     Indicates end of options.
   1   VINTR          Interrupt character; 255 if none.  Similarly for the
                      other characters. Not all of these characters are
                      supported on all systems.
   2   VQUIT          The quit character (sends SIGQUIT signal on POSIX
                      systems).
   3   VERASE         Erase the character to left of the cursor.
   4   VKILL          Kill the current input line.
   5   VEOF           End-of-file character (sends EOF from the terminal).
   6   VEOL           End-of-line character in addition to carriage return
                      and/or linefeed.
   7   VEOL2          Additional end-of-line character.
   8   VSTART         Continues paused output (normally control-Q).
   9   VSTOP          Pauses output (normally control-S).
   10  VSUSP          Suspends the current program.
   11  VDSUSP         Another suspend character.
   12  VREPRINT       Reprints the current input line.
   13  VWERASE        Erases a word left of cursor.
   14  VLNEXT         Enter the next character typed literally, even if it
                      is a special character
   15  VFLUSH         Character to flush output.
   16  VSWTCH         Switch to a different shell layer.
   17  VSTATUS        Prints system status line (load, command, pid etc).
   18  VDISCARD       Toggles the flushing of terminal output.
   30  IGNPAR         The ignore parity flag.  The parameter SHOULD be 0 if
                      this flag is FALSE set, and 1 if it is TRUE.
   31  PARMRK         Mark parity and framing errors.
   32  INPCK          Enable checking of parity errors.
   33  ISTRIP         Strip 8th bit off characters.



Ylonen, et. al.         Expires January 18, 2002               [Page 16]

Internet-Draft           SSH Connection Protocol               July 2001


   34  INLCR          Map NL into CR on input.
   35  IGNCR          Ignore CR on input.
   36  ICRNL          Map CR to NL on input.
   37  IUCLC          Translate uppercase characters to lowercase.
   38  IXON           Enable output flow control.
   39  IXANY          Any char will restart after stop.
   40  IXOFF          Enable input flow control.
   41  IMAXBEL        Ring bell on input queue full.
   50  ISIG           Enable signals INTR, QUIT, [D]SUSP.
   51  ICANON         Canonicalize input lines.
   52  XCASE          Enable input and output of uppercase characters by
                      preceding their lowercase equivalents with `\'.
   53  ECHO           Enable echoing.
   54  ECHOE          Visually erase chars.
   55  ECHOK          Kill character discards current line.
   56  ECHONL         Echo NL even if ECHO is off.
   57  NOFLSH         Don't flush after interrupt.
   58  TOSTOP         Stop background jobs from output.
   59  IEXTEN         Enable extensions.
   60  ECHOCTL        Echo control characters as ^(Char).
   61  ECHOKE         Visual erase for line kill.
   62  PENDIN         Retype pending input.
   70  OPOST          Enable output processing.
   71  OLCUC          Convert lowercase to uppercase.
   72  ONLCR          Map NL to CR-NL.
   73  OCRNL          Translate carriage return to newline (output).
   74  ONOCR          Translate newline to carriage return-newline
                      (output).
   75  ONLRET         Newline performs a carriage return (output).
   90  CS7            7 bit mode.
   91  CS8            8 bit mode.
   92  PARENB         Parity enable.
   93  PARODD         Odd parity, else even.

   128 TTY_OP_ISPEED  Specifies the input baud rate in bits per second.
   129 TTY_OP_OSPEED  Specifies the output baud rate in bits per second.


   7. Summary of Message Numbers

     #define SSH_MSG_GLOBAL_REQUEST                  80
     #define SSH_MSG_REQUEST_SUCCESS                 81
     #define SSH_MSG_REQUEST_FAILURE                 82
     #define SSH_MSG_CHANNEL_OPEN                    90
     #define SSH_MSG_CHANNEL_OPEN_CONFIRMATION       91
     #define SSH_MSG_CHANNEL_OPEN_FAILURE            92
     #define SSH_MSG_CHANNEL_WINDOW_ADJUST           93
     #define SSH_MSG_CHANNEL_DATA                    94



Ylonen, et. al.         Expires January 18, 2002               [Page 17]

Internet-Draft           SSH Connection Protocol               July 2001


     #define SSH_MSG_CHANNEL_EXTENDED_DATA           95
     #define SSH_MSG_CHANNEL_EOF                     96
     #define SSH_MSG_CHANNEL_CLOSE                   97
     #define SSH_MSG_CHANNEL_REQUEST                 98
     #define SSH_MSG_CHANNEL_SUCCESS                 99
     #define SSH_MSG_CHANNEL_FAILURE                 100


   8. Security Considerations

      This protocol is assumed to run on top of a secure, authenticated
      transport.  User authentication and protection against network-
      level attacks are assumed to be provided by the underlying
      protocols.

      This protocol can, however, be used to execute commands on remote
      machines.  The protocol also permits the server to run commands on
      the client.  Implementations may wish to disallow this to prevent
      an attacker from coming from the server machine to the client
      machine.

      X11 forwarding provides major security improvements over normal
      cookie-based X11 forwarding.  The cookie never needs to be
      transmitted in the clear, and traffic is encrypted and integrity-
      protected.  No useful authentication data will remain on the
      server machine after the connection has been closed.  On the other
      hand, in some situations a forwarded X11 connection might be used
      to get access to the local X server across security perimeters.

      Port forwardings can potentially allow an intruder to cross
      security perimeters such as firewalls.  They do not offer anything
      fundamentally new that a user could not do otherwise; however,
      they make opening tunnels very easy.  Implementations should allow
      policy control over what can be forwarded.  Administrators should
      be able to deny forwardings where appropriate.

      Since this protocol normally runs inside an encrypted tunnel,
      firewalls will not be able to examine the traffic.

      It is RECOMMENDED that implementations disable all the potentially
      dangerous features (e.g.  agent forwarding, X11 forwarding, and
      TCP/IP forwarding) if the host key has changed.

   9. Trademark Issues

      As of this writing, SSH Communications Security Oy claims ssh as
      its trademark.  As with all IPR claims the IETF takes no position
      regarding the validity or scope of this trademark claim.



Ylonen, et. al.         Expires January 18, 2002               [Page 18]

Internet-Draft           SSH Connection Protocol               July 2001


   10. Additional Information

      The current document editor is: Darren.Moffat@Sun.COM.  Comments
      on this internet draft should be sent to the IETF SECSH working
      group, details at: http://ietf.org/html.charters/secsh-
      charter.html

References

      [RFC1766]       Alvestrand, H., "Tags for the Identification of
                      Languages", RFC 1766, March 1995.

      [RFC1884]       Hinden, R., Deering, S. and Editors, "IP Version 6
                      Addressing Architecture", RFC 1884, December 1995.

      [RFC2279]       Yergeau, F., "UTF-8, a transformation format of
                      ISO 10646", RFC 2279, January 1998.

      [SCHEIFLER]     Scheifler, R., "X Window System : The Complete
                      Reference to Xlib, X Protocol, Icccm, Xlfd, 3rd
                      edition.", Digital Press ISBN 1555580882, Feburary
                      1992.

      [POSIX]         ISO/IEC, 9945-1., "Information technology --
                      Portable Operating System Interface  (POSIX)-Part
                      1: System Application Program Interface (API) C
                      Language", ANSI/IEE Std 1003.1, July 1996.

      [SSH-ARCH]      Ylonen, T., "SSH Protocol Architecture", I-D
                      draft-ietf-architecture-09.txt, July 2001.

      [SSH-TRANS]     Ylonen, T., "SSH Transport Layer Protocol", I-D
                      draft-ietf-transport-11.txt, July 2001.

      [SSH-USERAUTH]  Ylonen, T., "SSH Authentication Protocol", I-D
                      draft-ietf-userauth-11.txt, July 2001.

      [SSH-CONNECT]   Ylonen, T., "SSH Connection Protocol", I-D draft-
                      ietf-connect-11.txt, July 2001.












Ylonen, et. al.         Expires January 18, 2002               [Page 19]

Internet-Draft           SSH Connection Protocol               July 2001


Authors' Addresses

   Tatu Ylonen
   SSH Communications Security Corp
   Fredrikinkatu 42
   HELSINKI  FIN-00100
   Finland

   EMail: ylo@ssh.com


   Tero Kivinen
   SSH Communications Security Corp
   Fredrikinkatu 42
   HELSINKI  FIN-00100
   Finland

   EMail: kivinen@ssh.com


   Markku-Juhani O. Saarinen
   University of Jyvaskyla


   Timo J. Rinne
   SSH Communications Security Corp
   Fredrikinkatu 42
   HELSINKI  FIN-00100
   Finland

   EMail: tri@ssh.com


   Sami Lehtinen
   SSH Communications Security Corp
   Fredrikinkatu 42
   HELSINKI  FIN-00100
   Finland

   EMail: sjl@ssh.com











Ylonen, et. al.         Expires January 18, 2002               [Page 20]

Internet-Draft           SSH Connection Protocol               July 2001


Full Copyright Statement

      Copyright (C) The Internet Society (2001).  All Rights Reserved.

      This document and translations of it may be copied and furnished
      to others, and derivative works that comment on or otherwise
      explain it or assist in its implementation may be prepared,
      copied, published and distributed, in whole or in part, without
      restriction of any kind, provided that the above copyright notice
      and this paragraph are included on all such copies and derivative
      works.  However, this document itself may not be modified in any
      way, such as by removing the copyright notice or references to the
      Internet Society or other Internet organizations, except as needed
      for the purpose of developing Internet standards in which case the
      procedures for copyrights defined in the Internet Standards
      process must be followed, or as required to translate it into
      languages other than English.

      The limited permissions granted above are perpetual and will not
      be revoked by the Internet Society or its successors or assigns.

      This document and the information contained herein is provided on
      an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
      ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR
      IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
      THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
      WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

      Funding for the RFC Editor function is currently provided by the
      Internet Society.



















Ylonen, et. al.         Expires January 18, 2002               [Page 21]


Html markup produced by rfcmarkup 1.109, available from https://tools.ietf.org/tools/rfcmarkup/