draft-ietf-tcpm-urgent-data-04.txt   draft-ietf-tcpm-urgent-data-05.txt 
TCP Maintenance and Minor F. Gont TCP Maintenance and Minor F. Gont
Extensions (tcpm) UTN/FRH Extensions (tcpm) UTN/FRH
Internet-Draft A. Yourtchenko Internet-Draft A. Yourtchenko
Updates: 793, 1011, 1122 Cisco Updates: 793, 1011, 1122 Cisco
(if approved) March 3, 2010 (if approved) March 4, 2010
Intended status: Standards Track Intended status: Standards Track
Expires: September 4, 2010 Expires: September 5, 2010
On the implementation of the TCP urgent mechanism On the implementation of the TCP urgent mechanism
draft-ietf-tcpm-urgent-data-04.txt draft-ietf-tcpm-urgent-data-05.txt
Abstract Abstract
This document analyzes how current TCP implementations process TCP This document analyzes how current TCP implementations process TCP
urgent indications, and how the behavior of some widely-deployed urgent indications, and how the behavior of some widely-deployed
middle-boxes affect how urgent indications are processed by end middle-boxes affect how urgent indications are processed by end
systems. This document updates the relevant specifications such that systems. This document updates the relevant specifications such that
they accommodate current practice in processing TCP urgent they accommodate current practice in processing TCP urgent
indications, provides advice to applications that make use of the indications, provides advice to applications that make use of the
urgent mechanism, and raises awareness about the reliability of TCP urgent mechanism, and raises awareness about the reliability of TCP
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on September 4, 2010. This Internet-Draft will expire on September 5, 2010.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
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A.2. Linux . . . . . . . . . . . . . . . . . . . . . . . . . . 10 A.2. Linux . . . . . . . . . . . . . . . . . . . . . . . . . . 10
A.3. NetBSD . . . . . . . . . . . . . . . . . . . . . . . . . . 10 A.3. NetBSD . . . . . . . . . . . . . . . . . . . . . . . . . . 10
A.4. OpenBSD . . . . . . . . . . . . . . . . . . . . . . . . . 11 A.4. OpenBSD . . . . . . . . . . . . . . . . . . . . . . . . . 11
A.5. Cisco IOS software . . . . . . . . . . . . . . . . . . . . 11 A.5. Cisco IOS software . . . . . . . . . . . . . . . . . . . . 11
A.6. Microsoft Windows 2000, Service Pack 4 . . . . . . . . . . 11 A.6. Microsoft Windows 2000, Service Pack 4 . . . . . . . . . . 11
A.7. Microsoft Windows 2008 . . . . . . . . . . . . . . . . . . 11 A.7. Microsoft Windows 2008 . . . . . . . . . . . . . . . . . . 11
A.8. Microsoft Windows 95 . . . . . . . . . . . . . . . . . . . 12 A.8. Microsoft Windows 95 . . . . . . . . . . . . . . . . . . . 12
Appendix B. Changes from previous versions of the draft (to Appendix B. Changes from previous versions of the draft (to
be removed by the RFC Editor before publishing be removed by the RFC Editor before publishing
this document as an RFC) . . . . . . . . . . . . . . 12 this document as an RFC) . . . . . . . . . . . . . . 12
B.1. Changes from draft-ietf-tcpm-urgent-data-03 . . . . . . . 12 B.1. Changes from draft-ietf-tcpm-urgent-data-04 . . . . . . . 12
B.2. Changes from draft-ietf-tcpm-urgent-data-02 . . . . . . . 12 B.2. Changes from draft-ietf-tcpm-urgent-data-03 . . . . . . . 12
B.3. Changes from draft-ietf-tcpm-urgent-data-01 . . . . . . . 12 B.3. Changes from draft-ietf-tcpm-urgent-data-02 . . . . . . . 12
B.4. Changes from draft-ietf-tcpm-urgent-data-00 . . . . . . . 12 B.4. Changes from draft-ietf-tcpm-urgent-data-01 . . . . . . . 12
B.5. Changes from draft-gont-tcpm-urgent-data-01 . . . . . . . 12 B.5. Changes from draft-ietf-tcpm-urgent-data-00 . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 B.6. Changes from draft-gont-tcpm-urgent-data-01 . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction 1. Introduction
This document analyzes how some current TCP implementations process This document analyzes how some current TCP implementations process
TCP urgent indications, and how the behavior of some widely-deployed TCP urgent indications, and how the behavior of some widely-deployed
middle-boxes affect the processing of urgent indications by hosts. middle-boxes affect the processing of urgent indications by hosts.
This document updates RFC 793 [RFC0793], RFC 1011 [RFC1011], and RFC This document updates RFC 793 [RFC0793], RFC 1011 [RFC1011], and RFC
1122 [RFC1122] such that they accommodate current practice in 1122 [RFC1122] such that they accommodate current practice in
processing TCP urgent indications, provides advice to applications processing TCP urgent indications, provides advice to applications
using the urgent mechanism, and raises awareness about the using the urgent mechanism, and raises awareness about the
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to stimulate the receiving user to accept some "urgent data" and to to stimulate the receiving user to accept some "urgent data" and to
permit the receiving TCP to indicate to the receiving user when all permit the receiving TCP to indicate to the receiving user when all
the currently known urgent data have been received by the user. the currently known urgent data have been received by the user.
The TCP urgent mechanism permits a point in the data stream to be The TCP urgent mechanism permits a point in the data stream to be
designated as the end of urgent information. Whenever this point is designated as the end of urgent information. Whenever this point is
in advance of the receive sequence number (RCV.NXT) at the receiving in advance of the receive sequence number (RCV.NXT) at the receiving
TCP, that TCP must tell the user to go into "urgent mode"; when the TCP, that TCP must tell the user to go into "urgent mode"; when the
receive sequence number catches up to the urgent pointer, the TCP receive sequence number catches up to the urgent pointer, the TCP
must tell user to go into "normal mode" [RFC0793]. This means, for must tell user to go into "normal mode" [RFC0793]. This means, for
example, that data that were received as "normal data" might become example, that data that was received as "normal data" might become
"urgent data" if an urgent indication is received in some successive "urgent data" if an urgent indication is received in some successive
TCP segment before those data are consumed by the TCP user. TCP segment before that data is consumed by the TCP user.
The URG control flag indicates that the "Urgent Pointer" field is The URG control flag indicates that the "Urgent Pointer" field is
meaningful and must be added to the segment sequence number to yield meaningful and must be added to the segment sequence number to yield
the urgent pointer. The absence of this flag indicates that there is the urgent pointer. The absence of this flag indicates that there is
no urgent data outstanding [RFC0793]. no urgent data outstanding [RFC0793].
The TCP urgent mechanism is NOT a mechanism for sending "out-of-band" The TCP urgent mechanism is NOT a mechanism for sending "out-of-band"
data: the so-called "urgent data" should be delivered "in-line" to data: the so-called "urgent data" should be delivered "in-line" to
the TCP user. the TCP user.
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Unfortunately, virtually all TCP implementations process TCP urgent Unfortunately, virtually all TCP implementations process TCP urgent
data differently. By default, the last byte of "urgent data" is data differently. By default, the last byte of "urgent data" is
delivered "out of band" to the application. That is, it is not delivered "out of band" to the application. That is, it is not
delivered as part of the normal data stream. For example, the "out delivered as part of the normal data stream. For example, the "out
of band" byte is read by an application when a recv(2) system call of band" byte is read by an application when a recv(2) system call
with the MSG_OOB flag set is issued. with the MSG_OOB flag set is issued.
Most implementations provide a socket option (SO_OOBINLINE) that Most implementations provide a socket option (SO_OOBINLINE) that
allows an application to override the (broken) default processing of allows an application to override the (broken) default processing of
urgent data, so that they are delivered "in band" to the application, urgent data, so that it is delivered "in band" to the application,
thus providing the semantics intended by the IETF specifications. thus providing the semantics intended by the IETF specifications.
3.2. Semantics of the Urgent Pointer 3.2. Semantics of the Urgent Pointer
All the popular implementations that the authors of this document All the popular implementations that the authors of this document
have been able to test interpret the semantics of the TCP Urgent have been able to test interpret the semantics of the TCP Urgent
Pointer as specified in Section 3.1 of RFC 793. This means that even Pointer as specified in Section 3.1 of RFC 793. This means that even
when RFC 1122 officially updated RFC 793 to clarify the ambiguity in when RFC 1122 officially updated RFC 793 to clarify the ambiguity in
the semantics of the Urgent Pointer, this clarification was never the semantics of the Urgent Pointer, this clarification was never
reflected into actual implementations (i.e., virtually all reflected into actual implementations (i.e., virtually all
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As a result of the issues discussed in Section 3.2 and Section 3.4, As a result of the issues discussed in Section 3.2 and Section 3.4,
new applications SHOULD NOT employ the TCP urgent mechanism. new applications SHOULD NOT employ the TCP urgent mechanism.
However, TCP implementations MUST still include support for the However, TCP implementations MUST still include support for the
urgent mechanism such that existing applications can still use it. urgent mechanism such that existing applications can still use it.
6. Advice to applications that make use of the urgent mechanism 6. Advice to applications that make use of the urgent mechanism
Even though applications SHOULD NOT employ the urgent mechanism, Even though applications SHOULD NOT employ the urgent mechanism,
applications that still decide to employ it MUST set the SO_OOBINLINE applications that still decide to employ it MUST set the SO_OOBINLINE
socket option, such that "urgent data" are delivered inline, as socket option, such that "urgent data" is delivered inline, as
intended by the IETF specifications. intended by the IETF specifications.
7. Security Considerations 7. Security Considerations
Given that there are two different interpretations of the semantics Given that there are two different interpretations of the semantics
of the Urgent Pointer in current implementations (e.g., depending on of the Urgent Pointer in current implementations (e.g., depending on
the value of the tcp_stdurg sysctl), and that middle-boxes (such as the value of the tcp_stdurg sysctl), and that middle-boxes (such as
packet scrubbers) or the end-systems themselves could cause the packet scrubbers) or the end-systems themselves could cause the
urgent data to be processed "in band", there exists ambiguity in how urgent data to be processed "in band", there exists ambiguity in how
"urgent data" sent by a TCP will be processed by the intended "urgent data" sent by a TCP will be processed by the intended
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Linux supports only one byte of urgent data. That is, only the byte Linux supports only one byte of urgent data. That is, only the byte
preceding the Urgent Pointer is considered as "urgent data". preceding the Urgent Pointer is considered as "urgent data".
A.3. NetBSD A.3. NetBSD
NetBSD 5.0.1 [NetBSD] interprets the semantics of the urgent pointer NetBSD 5.0.1 [NetBSD] interprets the semantics of the urgent pointer
as specified in Section 4 of this document. It does not provide any as specified in Section 4 of this document. It does not provide any
sysctl to override this behavior. sysctl to override this behavior.
NetBSD provides the SO_OOBINLINE socket option that, when set, causes NetBSD provides the SO_OOBINLINE socket option that, when set, causes
TCP "urgent data" to remain "in band". That is, they will be TCP "urgent data" to remain "in band". That is, it will be
accessible by the read(2) call or the recv(2) call without the accessible by the read(2) call or the recv(2) call without the
MSG_OOB flag. MSG_OOB flag.
NetBSD supports only one byte of urgent data. That is, only the byte NetBSD supports only one byte of urgent data. That is, only the byte
preceding the Urgent Pointer is considered as "urgent data". preceding the Urgent Pointer is considered as "urgent data".
A.4. OpenBSD A.4. OpenBSD
OpenBSD 4.2 [OpenBSD] interprets the semantics of the urgent pointer OpenBSD 4.2 [OpenBSD] interprets the semantics of the urgent pointer
as specified in Section 4 of this document. It does not provide any as specified in Section 4 of this document. It does not provide any
sysctl to override this behavior. sysctl to override this behavior.
OpenBSD provides the SO_OOBINLINE socket option that, when set, OpenBSD provides the SO_OOBINLINE socket option that, when set,
causes TCP urgent data to remain "in band". That is, they will be causes TCP urgent data to remain "in band". That is, it will be
accessible by the read(2) or recv(2) calls without the MSG_OOB flag. accessible by the read(2) or recv(2) calls without the MSG_OOB flag.
OpenBSD supports only one byte of urgent data. That is, only the OpenBSD supports only one byte of urgent data. That is, only the
byte preceding the Urgent Pointer is considered as "urgent data". byte preceding the Urgent Pointer is considered as "urgent data".
A.5. Cisco IOS software A.5. Cisco IOS software
Cisco IOS Software Releases 12.2(18)SXF7, 12.4(15)T7 interpret the Cisco IOS Software Releases 12.2(18)SXF7, 12.4(15)T7 interpret the
semantics of the urgent pointer as specified in Section 4 of this semantics of the urgent pointer as specified in Section 4 of this
document. document.
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BSDUrgent system-wide variable to override this behavior, BSDUrgent system-wide variable to override this behavior,
interpreting the Urgent Pointer as specified in RFC 1122 [RFC1122]. interpreting the Urgent Pointer as specified in RFC 1122 [RFC1122].
Windows 95 supports only one byte of urgent data. That is, only the Windows 95 supports only one byte of urgent data. That is, only the
byte preceding the Urgent Pointer is considered as "urgent data". byte preceding the Urgent Pointer is considered as "urgent data".
[Windows95] [Windows95]
Appendix B. Changes from previous versions of the draft (to be removed Appendix B. Changes from previous versions of the draft (to be removed
by the RFC Editor before publishing this document as an by the RFC Editor before publishing this document as an
RFC) RFC)
B.1. Changes from draft-ietf-tcpm-urgent-data-03 B.1. Changes from draft-ietf-tcpm-urgent-data-04
o Fixes grammar errors wrt the term "data" (thanks to David Borman,
once again ;-) )
B.2. Changes from draft-ietf-tcpm-urgent-data-03
o Addresses feedback sent by David Borman, and nit pointed out by o Addresses feedback sent by David Borman, and nit pointed out by
John Heffner. John Heffner.
B.2. Changes from draft-ietf-tcpm-urgent-data-02 B.3. Changes from draft-ietf-tcpm-urgent-data-02
o Addresses WGLC feedback submitted by Michael Welzl, Anantha o Addresses WGLC feedback submitted by Michael Welzl, Anantha
Ramaiah, and Wesley Eddy. Ramaiah, and Wesley Eddy.
B.3. Changes from draft-ietf-tcpm-urgent-data-01 B.4. Changes from draft-ietf-tcpm-urgent-data-01
o Fixes reference to Cisco IOS Software (layer 8+ stuff ;-) ). o Fixes reference to Cisco IOS Software (layer 8+ stuff ;-) ).
o Cleaned-up Appendix A.5. o Cleaned-up Appendix A.5.
B.4. Changes from draft-ietf-tcpm-urgent-data-00 B.5. Changes from draft-ietf-tcpm-urgent-data-00
o Minor editorial changes. o Minor editorial changes.
o Incorporated the specific changes/advice stated in o Incorporated the specific changes/advice stated in
http://www.ietf.org/mail-archive/web/tcpm/current/msg04548.html in http://www.ietf.org/mail-archive/web/tcpm/current/msg04548.html in
different sections (Section 4, Section 5, Section 6). different sections (Section 4, Section 5, Section 6).
B.5. Changes from draft-gont-tcpm-urgent-data-01 B.6. Changes from draft-gont-tcpm-urgent-data-01
o Draft resubmitted as draft-ietf, as a result of wg consensus on o Draft resubmitted as draft-ietf, as a result of wg consensus on
adopting the document as a tcpm wg item. adopting the document as a tcpm wg item.
Authors' Addresses Authors' Addresses
Fernando Gont Fernando Gont
Universidad Tecnologica Nacional / Facultad Regional Haedo Universidad Tecnologica Nacional / Facultad Regional Haedo
Evaristo Carriego 2644 Evaristo Carriego 2644
Haedo, Provincia de Buenos Aires 1706 Haedo, Provincia de Buenos Aires 1706
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