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 toShow full document text