On the Implementation of the TCP Urgent Mechanism
RFC 6093
Internet Engineering Task Force (IETF) F. Gont
Request for Comments: 6093 UTN/FRH
Updates: 793, 1011, 1122 A. Yourtchenko
Category: Standards Track Cisco
ISSN: 2070-1721 January 2011
On the Implementation of the TCP Urgent Mechanism
Abstract
This document analyzes how current TCP implementations process TCP
urgent indications and how the behavior of some widely deployed
middleboxes affects how end systems process urgent indications. This
document updates the relevant specifications such that they
accommodate current practice in processing TCP urgent indications,
raises awareness about the reliability of TCP urgent indications in
the Internet, and recommends against the use of urgent indications
(but provides advice to applications that do).
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6093.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Gont & Yourtchenko Standards Track [Page 1]
RFC 6093 On the TCP Urgent Mechanism January 2011
Table of Contents
1. Introduction ....................................................3
2. Specification of the TCP Urgent Mechanism .......................3
2.1. Semantics of Urgent Indications ............................3
2.2. Semantics of the Urgent Pointer ............................4
2.3. Allowed Length of "Urgent Data" ............................4
3. Current Implementation Practice of the TCP Urgent Mechanism .....5
3.1. Semantics of Urgent Indications ............................5
3.2. Semantics of the Urgent Pointer ............................5
3.3. Allowed Length of "Urgent Data" ............................6
3.4. Interaction of Middleboxes with TCP Urgent Indications .....6
4. Updating RFC 793, RFC 1011, and RFC 1122 ........................6
5. Advice to New Applications Employing TCP ........................7
6. Advice to Applications That Make Use of the Urgent Mechanism ....7
7. Security Considerations .........................................7
8. Acknowledgements ................................................8
9. References ......................................................8
9.1. Normative References .......................................8
9.2. Informative References .....................................8
Appendix A. Survey of the Processing of TCP Urgent
Indications by Some Popular TCP Implementations ......10
A.1. FreeBSD ...................................................10
A.2. Linux .....................................................10
A.3. NetBSD ....................................................10
A.4. OpenBSD ...................................................11
A.5. Cisco IOS software ........................................11
A.6. Microsoft Windows 2000, Service Pack 4 ....................11
A.7. Microsoft Windows 2008 ....................................11
A.8. Microsoft Windows 95 ......................................11
Gont & Yourtchenko Standards Track [Page 2]
RFC 6093 On the TCP Urgent Mechanism January 2011
1. Introduction
This document analyzes how some current TCP implementations process
TCP urgent indications, and how the behavior of some widely deployed
middleboxes affects the processing of urgent indications by hosts.
This document updates RFC 793 [RFC0793], RFC 1011 [RFC1011], and RFC
1122 [RFC1122] such that they accommodate current practice in
processing TCP urgent indications. It also provides advice to
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