The Secure Shell (SSH) Session Channel Break Extension
RFC 4335
| Document | Type | RFC - Proposed Standard (January 2006; Errata) | |
|---|---|---|---|
| Authors | Phillip Remaker , Joseph Galbraith | ||
| Last updated | 2015-10-14 | ||
| Stream | IETF | ||
| Formats | plain text html pdf htmlized bibtex | ||
| Stream | WG state | WG Document | |
| Document shepherd | No shepherd assigned | ||
| IESG | IESG state | RFC 4335 (Proposed Standard) | |
| Action Holders |
(None)
|
||
| Consensus Boilerplate | Unknown | ||
| Telechat date | |||
| Responsible AD | Sam Hartman | ||
| Send notices to | (None) | ||
Network Working Group J. Galbraith
Request for Comments: 4335 VanDyke Software
Category: Standards Track P. Remaker
Cisco Systems, Inc
January 2006
The Secure Shell (SSH) Session Channel Break Extension
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
The Session Channel Break Extension provides a means to send a BREAK
signal over a Secure Shell (SSH) terminal session.
Table of Contents
1. Introduction ....................................................2
2. Conventions Used in This Document ...............................2
3. The Break Request ...............................................3
4. Security Considerations .........................................4
5. IANA Considerations .............................................4
6. References ......................................................4
6.1. Normative References .......................................4
6.2. Informative References .....................................5
Galbraith & Remaker Standards Track [Page 1]
RFC 4335 SSH Break Extension January 2006
1. Introduction
The Secure Shell (SSH) [5] session channel provides a mechanism for
the client-user to interactively enter commands and receive output
from a remote host while taking advantage of the SSH transport's
privacy and integrity features. SSH is increasingly being used to
replace Telnet for terminal access applications.
A common application of the Telnet protocol is the "Console Server"
[7] whereby a Telnet Network Virtual Terminal (NVT) can be connected
to a physical RS-232/V.24 asynchronous port, making the Telnet NVT
appear as a locally attached terminal to that port, and making that
physical port appear as a network-addressable device. A number of
major computer equipment vendors provide high-level administrative
functions through an asynchronous serial port and generally expect
the attached terminal to be capable of sending a BREAK signal.
A BREAK signal is defined as the TxD signal being held in a SPACE
("0") state for a time greater than a whole character time. In
practice, a BREAK signal is typically 250 to 500 ms in length.
The Telnet protocol furnishes a means to send a "BREAK" signal, which
RFC 854 [1] defines as "a signal outside the USASCII set which is
currently given local meaning within many systems". Console Server
vendors interpret the TELNET BREAK signal as a physical BREAK signal,
which can then allow access to the full range of administrative
functions available on an asynchronous serial console port.
The lack of a similar facility in the SSH session channel has forced
users to continue the use of Telnet for the "Console Server"
function.
2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [2].
The "byte", "boolean", "uint32", and "string" data types are defined
in [3].
Galbraith & Remaker Standards Track [Page 2]
RFC 4335 SSH Break Extension January 2006
3. The Break Request
The following channel-specific request can be sent over a session
channel (as described in [4]) to request that the remote host perform
a BREAK operation.
byte SSH_MSG_CHANNEL_REQUEST
uint32 recipient channel
string "break"
boolean want_reply
uint32 break-length in milliseconds
If the BREAK length cannot be controlled by the application receiving
this request, the BREAK length parameter SHOULD be ignored and the
default BREAK signal length of the chipset or underlying chipset
driver SHOULD be sent.
If the application receiving this request can control the BREAK
length, the following suggestions are made regarding BREAK duration.
If a BREAK duration request of greater than 3000 ms is received, it
SHOULD be interpreted as a request for a 3000 ms BREAK. This
safeguard prevents an unreasonably long BREAK request from causing a
port to become unavailable for as long as 49.7 days while executing
the BREAK. Applications that require a longer BREAK may choose to
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