draft-ietf-tcpm-urgent-data-02.txt   draft-ietf-tcpm-urgent-data-03.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
Intended status: Standards Track Cisco Intended status: Standards Track Cisco
Expires: May 30, 2010 November 26, 2009 Expires: August 23, 2010 February 19, 2010
On the implementation of the TCP urgent mechanism On the implementation of the TCP urgent mechanism
draft-ietf-tcpm-urgent-data-02.txt draft-ietf-tcpm-urgent-data-03.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 May 30, 2010. This Internet-Draft will expire on August 23, 2010.
Copyright Notice Copyright Notice
Copyright (c) 2009 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
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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
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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2. Specification of the TCP urgent mechanism . . . . . . . . . . 3 2. Specification of the TCP urgent mechanism . . . . . . . . . . 3
2.1. Semantics of urgent inications . . . . . . . . . . . . . . 3 2.1. Semantics of urgent inications . . . . . . . . . . . . . . 3
2.2. Semantics of the Urgent Pointer . . . . . . . . . . . . . 4 2.2. Semantics of the Urgent Pointer . . . . . . . . . . . . . 4
2.3. Allowed length of urgent data . . . . . . . . . . . . . . 4 2.3. Allowed length of urgent data . . . . . . . . . . . . . . 4
3. Current implementation practice of TCP urgent data . . . . . . 4 3. Current implementation practice of TCP urgent data . . . . . . 4
3.1. Semantics of urgent indications . . . . . . . . . . . . . 4 3.1. Semantics of urgent indications . . . . . . . . . . . . . 4
3.2. Semantics of the Urgent Pointer . . . . . . . . . . . . . 5 3.2. Semantics of the Urgent Pointer . . . . . . . . . . . . . 5
3.3. Allowed length of urgent data . . . . . . . . . . . . . . 5 3.3. Allowed length of urgent data . . . . . . . . . . . . . . 5
3.4. Interaction of middle-boxes with TCP urgent indications . 6 3.4. Interaction of middle-boxes with TCP urgent indications . 6
4. Updating RFC 1122 . . . . . . . . . . . . . . . . . . . . . . 6 4. Updating RFC 1122 . . . . . . . . . . . . . . . . . . . . . . 6
5. Advice to new applications employing TCP . . . . . . . . . . . 7 5. Advice to new applications employing TCP . . . . . . . . . . . 6
6. Advice to applications that make use of the urgent 6. Advice to applications that make use of the urgent
mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . 7 mechanism . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . . 8 10.1. Normative References . . . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . . 8 10.2. Informative References . . . . . . . . . . . . . . . . . . 8
Appendix A. Survey of the processing of TCP urgent Appendix A. Survey of the processing of TCP urgent
indications by some popular TCP implementations . . . 9 indications by some popular TCP implementations . . . 9
A.1. FreeBSD . . . . . . . . . . . . . . . . . . . . . . . . . 9 A.1. FreeBSD . . . . . . . . . . . . . . . . . . . . . . . . . 9
A.2. Linux . . . . . . . . . . . . . . . . . . . . . . . . . . 9 A.2. Linux . . . . . . . . . . . . . . . . . . . . . . . . . . 9
A.3. NetBSD . . . . . . . . . . . . . . . . . . . . . . . . . . 10 A.3. NetBSD . . . . . . . . . . . . . . . . . . . . . . . . . . 9
A.4. OpenBSD . . . . . . . . . . . . . . . . . . . . . . . . . 10 A.4. OpenBSD . . . . . . . . . . . . . . . . . . . . . . . . . 10
A.5. Cisco IOS software . . . . . . . . . . . . . . . . . . . . 10 A.5. Cisco IOS software . . . . . . . . . . . . . . . . . . . . 10
A.6. Microsoft Windows 2000, Service Pack 4 . . . . . . . . . . 10 A.6. Microsoft Windows 2000, Service Pack 4 . . . . . . . . . . 10
A.7. Microsoft Windows 2008 . . . . . . . . . . . . . . . . . . 11 A.7. Microsoft Windows 2008 . . . . . . . . . . . . . . . . . . 10
A.8. Microsoft Windows 95 . . . . . . . . . . . . . . . . . . . 11 A.8. Microsoft Windows 95 . . . . . . . . . . . . . . . . . . . 10
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) . . . . . . . . . . . . . . 11 this document as an RFC) . . . . . . . . . . . . . . 11
B.1. Changes from draft-ietf-tcpm-urgent-data-01 . . . . . . . 11 B.1. Changes from draft-ietf-tcpm-urgent-data-02 . . . . . . . 11
B.2. Changes from draft-ietf-tcpm-urgent-data-00 . . . . . . . 11 B.2. Changes from draft-ietf-tcpm-urgent-data-01 . . . . . . . 11
B.3. Changes from draft-gont-tcpm-urgent-data-01 . . . . . . . 11 B.3. Changes from draft-ietf-tcpm-urgent-data-00 . . . . . . . 11
B.4. Changes from draft-gont-tcpm-urgent-data-01 . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction 1. Introduction
TCP incorporates an "urgent mechanism" that allows the sending user This document analyzes how some current TCP implementations process
to stimulate the receiving user to accept some "urgent data" and to TCP urgent indications, and how the behavior of some widely-deployed
permit the receiving TCP to indicate to the receiving user when all
the currently known urgent data has been received by the user. This
mechanism permits a point in the data stream to be designated as the
end of urgent information. Whenever this point is 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 receive sequence
number catches up to the urgent pointer, the TCP must tell user to go
into "normal mode" [RFC0793].
The URG control flag indicates that the "Urgent Pointer" field is
meaningful and must be added to the segment sequence number to yield
the urgent pointer. The absence of this flag indicates that there is
no urgent data outstanding [RFC0793].
This document analyzes how current TCP implementations process 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 1122 [RFC1122] such that IT accommodates This document updates RFC 1122 [RFC1122] such that it accommodates
current practice in processing TCP urgent indications, provides current practice in processing TCP urgent indications, provides
advice to applications using urgent the urgent mechanism, and raises advice to applications using the urgent mechanism, and raises
awareness about the reliability of TCP urgent indications in the awareness about the reliability of TCP urgent indications in the
current Internet. current Internet.
Section 2 describes what the current IETF secifications state with Section 2 describes what the current IETF secifications state with
respect to TCP urgent indications. Section 3 describes how current respect to TCP urgent indications. Section 3 describes how some
TCP implementations actually process TCP urgent indications. current TCP implementations actually process TCP urgent indications.
Section 4 updates RFC 1122 [RFC1122] such that it accommodates Section 4 updates RFC 1122 [RFC1122] such that it accommodates
current practice in processing TCP urgent indications. Section 5 current practice in processing TCP urgent indications. Section 5
provides advice to to new applications employing TCP, with respect to provides advice to to new applications employing TCP, with respect to
the TCP urgent mechanism. Section 6 provides advice to existing the TCP urgent mechanism. Section 6 provides advice to existing
applications that use or rely on the the TCP urgent mechanism. applications that use or rely on the the TCP urgent mechanism.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. Specification of the TCP urgent mechanism 2. Specification of the TCP urgent mechanism
2.1. Semantics of urgent inications 2.1. Semantics of urgent inications
As discussed in Section 1, the TCP urgent mechanism permits a point TCP incorporates an "urgent mechanism" that allows the sending user
in the data stream to be designated as the end of urgent information. to stimulate the receiving user to accept some "urgent data" and to
Whenever this point is in advance of the receive sequence number permit the receiving TCP to indicate to the receiving user when all
(RCV.NXT) at the receiving TCP, that TCP must tell the user to go the currently known urgent data have been received by the user.
into "urgent mode"; when the receive sequence number catches up to
the urgent pointer, the TCP must tell user to go into "normal mode". The TCP urgent mechanism permits a point in the data stream to be
This means, for example, that data that were received as "normal designated as the end of urgent information. Whenever this point is
data" might become "urgent data" if an urgent indication is received in advance of the receive sequence number (RCV.NXT) at the receiving
in some successive TCP segment before those data are consumed by the TCP, that TCP must tell the user to go into "urgent mode"; when the
TCP user. receive sequence number catches up to the urgent pointer, the TCP
must tell user to go into "normal mode" [RFC0793]. This means, for
example, that data that were received as "normal data" might become
"urgent data" if an urgent indication is received in some successive
TCP segment before those data are consumed by the TCP user.
The URG control flag indicates that the "Urgent Pointer" field is
meaningful and must be added to the segment sequence number to yield
the urgent pointer. The absence of this flag indicates that there is
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.
2.2. Semantics of the Urgent Pointer 2.2. Semantics of the Urgent Pointer
There is some ambiguity in RFC 793 [RFC0793] with respect to the There is some ambiguity in RFC 793 [RFC0793] with respect to the
semantics of the Urgent Pointer. Section 3.1 (page 17) of RFC 793 semantics of the Urgent Pointer. Section 3.1 (page 17) of RFC 793
[RFC0793] states that the Urgent Pointer "communicates the current [RFC0793] states that the Urgent Pointer "communicates the current
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3. Current implementation practice of TCP urgent data 3. Current implementation practice of TCP urgent data
3.1. Semantics of urgent indications 3.1. Semantics of urgent indications
As discussed in Section 1, the TCP urgent mechanism simply permits a As discussed in Section 1, the TCP urgent mechanism simply permits a
point in the data stream to be designated as the end of urgent point in the data stream to be designated as the end of urgent
information, but does NOT provide a mechanism for sending out of band information, but does NOT provide a mechanism for sending out of band
data. data.
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 they are 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 never the semantics of the Urgent Pointer, this clarification never was
reflected into actual implementations (i.e., virtually all reflected into actual implementations (i.e., virtually all
implementations default to the semantics of the urgent pointer implementations default to the semantics of the urgent pointer
specified in Section 3.1 of RFC 793). specified in Section 3.1 of RFC 793).
Some operating systems provide a system-wide toggle to override this Some operating systems provide a system-wide toggle to override this
behavior, and interpret the semantics of the Urgent Pointer as behavior, and interpret the semantics of the Urgent Pointer as
clarified in RFC 1122. However, this system-wide toggle has been clarified in RFC 1122. However, this system-wide toggle has been
found to be inconsistent. For example, Linux provides the sysctl found to be inconsistent. For example, Linux provides the sysctl
"tcp_stdurg" (i.e., net.ivp4.tcp_stdurg) that, when set, supposedly "tcp_stdurg" (i.e., net.ivp4.tcp_stdurg) that, when set, supposedly
changes the system behavior to interpret the semantics of the TCP changes the system behavior to interpret the semantics of the TCP
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3.4. Interaction of middle-boxes with TCP urgent indications 3.4. Interaction of middle-boxes with TCP urgent indications
As a result of the publication of Network Intrusion Detection (NIDs) As a result of the publication of Network Intrusion Detection (NIDs)
evasion techniques based on TCP urgent indications [phrack], some evasion techniques based on TCP urgent indications [phrack], some
middle-boxes clear the urgent indications by clearing the URG flag middle-boxes clear the urgent indications by clearing the URG flag
and setting the Urgent Pointer to zero. This causes the "urgent and setting the Urgent Pointer to zero. This causes the "urgent
data" to become "in line" (that is, accessible by the read(2) call or data" to become "in line" (that is, accessible by the read(2) call or
the recv(2) call without the MSG_OOB flag) in the case of those TCP the recv(2) call without the MSG_OOB flag) in the case of those TCP
implementations that implement the urgent mechanism as out-of-band implementations that implement the urgent mechanism as out-of-band
data (as described in Section 3.1). Examples of such middle-boxes data (as described in Section 3.1). An example of such a middle-box
are Cisco PIX firewall [Cisco-PIX]. This should discourage is the Cisco PIX firewall [Cisco-PIX]. This should discourage
applications to depend on urgent indications for their correct applications from depending on urgent indications for their correct
operation, as urgent indications may not be not reliable in the operation, as urgent indications may not be not reliable in the
current Internet. current Internet.
4. Updating RFC 1122 4. Updating RFC 1122
Considering that as long as both the TCP sender and the TCP receiver Considering that as long as both the TCP sender and the TCP receiver
implement the same semantics for the Urgent Pointer there is no implement the same semantics for the Urgent Pointer there is no
functional difference in having the Urgent Pointer point to "the functional difference in having the Urgent Pointer point to "the
sequence number of the octet following the urgent data" vs. "the last sequence number of the octet following the urgent data" vs. "the last
octet of urgent data", and since all known implementations interpret octet of urgent data", and since all known implementations interpret
the semantics of the Urgent Pointer as pointing to "the sequence the semantics of the Urgent Pointer as pointing to "the sequence
number of the octet following the urgent data", hereby we update RFC number of the octet following the urgent data", hereby we update RFC
1122 [RFC1122] such that "the urgent pointer points to the sequence 1122 [RFC1122] such that "the urgent pointer points to the sequence
number of the octet following the urgent data" (in segments with the number of the octet following the urgent data" (in segments with the
URG control bit set), thus accommodating virtually all existing TCP URG control bit set), thus accommodating virtually all existing TCP
implementations. implementations.
5. Advice to new applications employing TCP 5. Advice to new applications employing TCP
As a result of the issues discussed in Section 3.4, new applications As a result of the issues discussed in Section 3.2 and Section 3.4,
SHOULD NOT employ the TCP urgent mechanism. However, TCP new applications SHOULD NOT employ the TCP urgent mechanism.
implementations MUST still include support for the urgent mechanism However, TCP implementations MUST still include support for the
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
Applications that employ the Sockets API MUST set the SO_OOBINLINE Even though applications SHOULD NOT employ the urgent mechanism,
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" are 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., depnding on of the Urgent Pointer in current implementations (e.g., depnding 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
skipping to change at page 8, line 46 skipping to change at page 8, line 40
might cause interoperability problems or undesired behavior in the might cause interoperability problems or undesired behavior in the
applications running on top of TCP. applications running on top of TCP.
8. IANA Considerations 8. IANA Considerations
This document has no actions for IANA. This document has no actions for IANA.
9. Acknowledgements 9. Acknowledgements
The authors of this document would like to thank (in alphabetical The authors of this document would like to thank (in alphabetical
order) David Borman, Alfred Hoenes, Carlos Pignataro, Anantha order) David Borman, Wesley Eddy, Alfred Hoenes, Carlos Pignataro,
Ramaiah, Joe Touch, and Dan Wing for providing valuable feedback on Anantha Ramaiah, Joe Touch, Michael Welzl, and Dan Wing for providing
earlier versions of this document. valuable feedback on earlier versions of this document.
Additionally, Fernando would like to thank David Borman and Joe Touch Additionally, Fernando would like to thank David Borman and Joe Touch
for a fruitful discussion about TCP urgent mode at IETF 73 for a fruitful discussion about TCP urgent mode at IETF 73
(Minneapolis). (Minneapolis).
10. References 10. References
10.1. Normative References 10.1. Normative References
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, [RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
RFC 793, September 1981. RFC 793, September 1981.
[RFC1122] Braden, R., "Requirements for Internet Hosts - [RFC1122] Braden, R., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, October 1989. Communication Layers", STD 3, RFC 1122, October 1989.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
skipping to change at page 10, line 18 skipping to change at page 10, line 11
[phrack] Ko, Y., Ko, S., and M. Ko, "NIDS Evasion Method named [phrack] Ko, Y., Ko, S., and M. Ko, "NIDS Evasion Method named
"SeolMa"", Phrack Magazine, Volume 0x0b, Issue 0x39, Phile "SeolMa"", Phrack Magazine, Volume 0x0b, Issue 0x39, Phile
#0x03 of 0x12 http://www.phrack.org/ #0x03 of 0x12 http://www.phrack.org/
issues.html?issue=57&id=3#article, 2001. issues.html?issue=57&id=3#article, 2001.
Appendix A. Survey of the processing of TCP urgent indications by some Appendix A. Survey of the processing of TCP urgent indications by some
popular TCP implementations popular TCP implementations
A.1. FreeBSD A.1. FreeBSD
FreeBSD [FreeBSD] interprets the semantics of the urgent pointer as FreeBSD 8.0 [FreeBSD] interprets the semantics of the urgent pointer
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.
FreeBSD provides the SO_OOBINLINE socket option that, when set, FreeBSD provides the SO_OOBINLINE socket option that, when set,
causes TCP "urgent data" to remain "in band". That is, it will be causes 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.
FreeBSD supports only one byte of urgent data. That is, only the FreeBSD 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.2. Linux A.2. Linux
Linux [Linux] interprets the semantics of the urgent pointer as Linux 2.6.15-53-386 [Linux] interprets the semantics of the urgent
specified in Section 4 of this document. It provides the pointer as specified in Section 4 of this document. It provides the
net.ipv4.tcp_stdurg sysctl to override this behavior to interpret the net.ipv4.tcp_stdurg sysctl to override this behavior to interpret the
Urgent Pointer as specified in RFC 1122 [RFC1122]. However, this Urgent Pointer as specified in RFC 1122 [RFC1122]. However, this
sysctl only affects the processing of incoming segments (the Urgent sysctl only affects the processing of incoming segments (the Urgent
Pointer in outgoing segments will still be set as specified in Pointer in outgoing segments will still be set as specified in
Section 4 of this document). Section 4 of this document).
Linux provides the SO_OOBINLINE socket option that, when set, causes Linux provides the SO_OOBINLINE socket option that, when set, causes
TCP "urgent data" to remain "in band". That is, it 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.
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 [NetBSD] interprets the semantics of the urgent pointer as NetBSD 5.0.1 [NetBSD] interprets the semantics of the urgent pointer
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, they 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 [OpenBSD] interprets the semantics of the urgent pointer as OpenBSD 4.2 [OpenBSD] interprets the semantics of the urgent pointer
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, they 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
skipping to change at page 12, line 16 skipping to change at page 12, line 4
Microsoft Windows 2008 interprets the semantics of the urgent pointer Microsoft Windows 2008 interprets the semantics of the urgent pointer
as specified in Section 4 of this document. as specified in Section 4 of this document.
A.8. Microsoft Windows 95 A.8. Microsoft Windows 95
Microsoft Windows 95 interprets the semantics of the urgent pointer Microsoft Windows 95 interprets the semantics of the urgent pointer
as specified in Section 4 of this document. It provides the as specified in Section 4 of this document. It provides the
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-01 B.1. Changes from draft-ietf-tcpm-urgent-data-02
o Addresses WGLC feedback submitted by Michael Welzl, Anantha
Ramaiah, and Wesley Eddy.
B.2. 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.2. Changes from draft-ietf-tcpm-urgent-data-00 B.3. 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.3. Changes from draft-gont-tcpm-urgent-data-01 B.4. 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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