Network Working Group T. Ylonen
Internet-Draft SSH Communications Security Corp
Expires: December 1, 2004 C. Lonvick, Ed.
Cisco Systems, Inc
June 2, 2004
SSH Connection Protocol
draft-ietf-secsh-connect-19.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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This Internet-Draft will expire on December 1, 2004.
Copyright Notice
Copyright (C) The Internet Society (2004). 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, 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.
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Table of Contents
1. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Conventions Used in This Document . . . . . . . . . . . . . . 3
4. Global Requests . . . . . . . . . . . . . . . . . . . . . . . 3
5. Channel Mechanism . . . . . . . . . . . . . . . . . . . . . . 4
5.1 Opening a Channel . . . . . . . . . . . . . . . . . . . . 4
5.2 Data Transfer . . . . . . . . . . . . . . . . . . . . . . 6
5.3 Closing a Channel . . . . . . . . . . . . . . . . . . . . 6
5.4 Channel-Specific Requests . . . . . . . . . . . . . . . . 7
6. Interactive Sessions . . . . . . . . . . . . . . . . . . . . . 8
6.1 Opening a Session . . . . . . . . . . . . . . . . . . . . 8
6.2 Requesting a Pseudo-Terminal . . . . . . . . . . . . . . . 8
6.3 X11 Forwarding . . . . . . . . . . . . . . . . . . . . . . 9
6.3.1 Requesting X11 Forwarding . . . . . . . . . . . . . . 9
6.3.2 X11 Channels . . . . . . . . . . . . . . . . . . . . . 10
6.4 Environment Variable Passing . . . . . . . . . . . . . . . 10
6.5 Starting a Shell or a Command . . . . . . . . . . . . . . 10
6.6 Session Data Transfer . . . . . . . . . . . . . . . . . . 11
6.7 Window Dimension Change Message . . . . . . . . . . . . . 12
6.8 Local Flow Control . . . . . . . . . . . . . . . . . . . . 12
6.9 Signals . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.10 Returning Exit Status . . . . . . . . . . . . . . . . . . 13
7. TCP/IP Port Forwarding . . . . . . . . . . . . . . . . . . . . 14
7.1 Requesting Port Forwarding . . . . . . . . . . . . . . . . 14
7.2 TCP/IP Forwarding Channels . . . . . . . . . . . . . . . . 15
8. Encoding of Terminal Modes . . . . . . . . . . . . . . . . . . 16
9. Summary of Message Numbers . . . . . . . . . . . . . . . . . . 18
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . 18
11. Security Considerations . . . . . . . . . . . . . . . . . . 18
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
12.1 Normative References . . . . . . . . . . . . . . . . . . . . 19
12.2 Informative References . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 20
Intellectual Property and Copyright Statements . . . . . . . . 21
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1. Contributors
The major original contributors of this document were: Tatu Ylonen,
Tero Kivinen, Timo J. Rinne, Sami Lehtinen (all of SSH
Communications Security Corp), and Markku-Juhani O. Saarinen
(University of Jyvaskyla). Darren Moffit was the original editor of
this document and also made very substantial contributions.
Additional contributors to this document include [need list].
Listing their names here does not mean that they endorse this
document, but that they have contributed to it.
Comments on this internet draft should be sent to the IETF SECSH
working group, details at:
http://ietf.org/html.charters/secsh-charter.html Note: This paragraph
will be removed before this document progresses to become an RFC.
2. 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 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.
3. Conventions Used in This Document
The keywords "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT",
and "MAY" that appear in this document are to be interpreted as
described in [RFC2119].
The used data types and terminology are specified in the architecture
document [SSH-ARCH].
The architecture document also discusses the algorithm naming
conventions that MUST be used with the SSH protocols.
4. 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.
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byte SSH_MSG_GLOBAL_REQUEST
string request name in US-ASCII only
boolean want reply
... request-specific data follows
Request names follow the DNS extensibility naming convention outlined
in [SSH-ARCH].
The recipient will respond to this message with
SSH_MSG_REQUEST_SUCCESS or SSH_MSG_REQUEST_FAILURE if `want reply' is
TRUE.
byte SSH_MSG_REQUEST_SUCCESS
..... response specific data
Usually the response specific data is non-existent.
If the recipient does not recognize or support the request, it simply
responds with SSH_MSG_REQUEST_FAILURE.
byte SSH_MSG_REQUEST_FAILURE
5. 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 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.
5.1 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 in US-ASCII only
uint32 sender channel
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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
string additional textual information in ISO-10646 UTF-8
encoding [RFC2279]
string language tag as defined in [RFC3066]
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
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5.2 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.
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
5.3 Closing a Channel
When a party will no longer send more data to a channel, it SHOULD
send SSH_MSG_CHANNEL_EOF.
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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.
5.4 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 in US-ASCII characters only
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.
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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.
request type names follow the DNS extensibility naming convention
outlined in [SSH-ARCH]
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.
6. 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.
6.1 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.
6.2 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
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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 8). 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.
6.3 X11 Forwarding
6.3.1 Requesting X11 Forwarding
X11 forwarding may be requested for a session by sending
byte SSH_MSG_CHANNEL_REQUEST
uint32 recipient channel
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".
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The x11 authentication cookie MUST be hexadecimal encoded.
X Protocol is documented in [SCHEIFLER].
6.3.2 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.
6.4 Environment Variable Passing
Environment variables may be passed to the shell/command to be
started later. Uncontrolled setting of environment variables in a
privileged process can be a security hazard. It is recommended that
implementations either maintain a list of allowable variable names or
only set environment variables after the server process has dropped
sufficient privileges.
byte SSH_MSG_CHANNEL_REQUEST
uint32 recipient channel
string "env"
boolean want reply
string variable name
string variable value
6.5 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.
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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 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 it from arbitrary output generated by 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.
Subsystem names follow the DNS extensibility naming convention
outlined in [SSH-ARCH].
6.6 Session Data Transfer
Data transfer for a session is done using SSH_MSG_CHANNEL_DATA and
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SSH_MSG_CHANNEL_EXTENDED_DATA packets and the window mechanism. The
extended data type SSH_EXTENDED_DATA_STDERR has been defined for
stderr data.
6.7 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.
6.8 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 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.
6.9 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.
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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.
6.10 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.
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 in ISO-10646 UTF-8 encoding
string language tag as defined in [RFC3066]
The signal name is one of the following (these are from [POSIX])
ABRT
ALRM
FPE
HUP
ILL
INT
KILL
PIPE
QUIT
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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].
7. TCP/IP Port Forwarding
7.1 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.
If a client passes 0 as port number to bind and has want reply TRUE
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then the server allocates the next available unprivileged port number
and replies with the following message, otherwise there is no
response specific data.
byte SSH_MSG_GLOBAL_REQUEST_SUCCESS
uint32 port that was bound on the server
A port forwarding can be canceled 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.
7.2 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
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
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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.
8. 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.
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.
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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.
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.
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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.
9. 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
#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
10. IANA Considerations
This document is part of a set. The IANA considerations for the SSH
protocol as defined in [SSH-ARCH], [SSH-TRANS], [SSH-USERAUTH], and
this document, are detailed in [SSH-NUMBERS].
11. 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.
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Full security considerations for this protocol are provided in
[SSH-ARCH]. Specific to this document, 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 without notice or explanation.
12. References
12.1 Normative References
[SSH-ARCH]
Ylonen, T. and C. Lonvick, "SSH Protocol Architecture",
I-D draft-ietf-architecture-16.txt, May 2004.
[SSH-TRANS]
Ylonen, T. and C. Lonvick, "SSH Transport Layer Protocol",
I-D draft-ietf-transport-18.txt, May 2004.
[SSH-USERAUTH]
Ylonen, T. and C. Lonvick, "SSH Authentication Protocol",
I-D draft-ietf-userauth-21.txt, May 2004.
[SSH-NUMBERS]
Ylonen, T. and C. Lonvick, "SSH Protocol Assigned
Numbers", I-D draft-ietf-assignednumbers-06.txt, May 2004.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
12.2 Informative References
[RFC1884] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 1884, December 1995.
[RFC2279] Yergeau, F., "UTF-8, a transformation format of ISO
10646", RFC 2279, January 1998.
[RFC3066] Alvestrand, H., "Tags for the Identification of
Languages", BCP 47, RFC 3066, January 2001.
[SCHEIFLER]
Scheifler, R., "X Window System : The Complete Reference
to Xlib, X Protocol, Icccm, Xlfd, 3rd edition.", Digital
Press ISBN 1555580882, February 1992.
[POSIX] ISO/IEC, 9945-1., "Information technology -- Portable
Operating System Interface (POSIX)-Part 1: System
Application Program Interface (API) C Language", ANSI/IEE
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Std 1003.1, July 1996.
Authors' Addresses
Tatu Ylonen
SSH Communications Security Corp
Fredrikinkatu 42
HELSINKI FIN-00100
Finland
EMail: ylo@ssh.com
Chris Lonvick (editor)
Cisco Systems, Inc
12515 Research Blvd.
Austin 78759
USA
EMail: clonvick@cisco.com
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