--- 1/draft-ietf-tcpm-urgent-data-04.txt 2010-03-05 07:11:41.000000000 +0100 +++ 2/draft-ietf-tcpm-urgent-data-05.txt 2010-03-05 07:11:41.000000000 +0100 @@ -1,21 +1,21 @@ TCP Maintenance and Minor F. Gont Extensions (tcpm) UTN/FRH Internet-Draft A. Yourtchenko Updates: 793, 1011, 1122 Cisco -(if approved) March 3, 2010 +(if approved) March 4, 2010 Intended status: Standards Track -Expires: September 4, 2010 +Expires: September 5, 2010 On the implementation of the TCP urgent mechanism - draft-ietf-tcpm-urgent-data-04.txt + draft-ietf-tcpm-urgent-data-05.txt Abstract This document analyzes how current TCP implementations process TCP urgent indications, and how the behavior of some widely-deployed middle-boxes affect how urgent indications are processed by end systems. This document updates the relevant specifications such that they accommodate current practice in processing TCP urgent indications, provides advice to applications that make use of the urgent mechanism, and raises awareness about the reliability of TCP @@ -35,21 +35,21 @@ and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at 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 (c) 2010 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 carefully, as they describe your rights and restrictions with respect @@ -86,26 +86,27 @@ 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 . . . . . . . . . . . . . . . . . . . 12 Appendix B. Changes from previous versions of the draft (to be removed by the RFC Editor before publishing this document as an RFC) . . . . . . . . . . . . . . 12 - B.1. Changes from draft-ietf-tcpm-urgent-data-03 . . . . . . . 12 - B.2. Changes from draft-ietf-tcpm-urgent-data-02 . . . . . . . 12 - B.3. Changes from draft-ietf-tcpm-urgent-data-01 . . . . . . . 12 - B.4. Changes from draft-ietf-tcpm-urgent-data-00 . . . . . . . 12 - B.5. Changes from draft-gont-tcpm-urgent-data-01 . . . . . . . 12 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 + B.1. Changes from draft-ietf-tcpm-urgent-data-04 . . . . . . . 12 + B.2. Changes from draft-ietf-tcpm-urgent-data-03 . . . . . . . 12 + B.3. Changes from draft-ietf-tcpm-urgent-data-02 . . . . . . . 12 + B.4. Changes from draft-ietf-tcpm-urgent-data-01 . . . . . . . 12 + B.5. Changes from draft-ietf-tcpm-urgent-data-00 . . . . . . . 12 + B.6. Changes from draft-gont-tcpm-urgent-data-01 . . . . . . . 13 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 1. Introduction This document analyzes how some 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. This document updates RFC 793 [RFC0793], RFC 1011 [RFC1011], and RFC 1122 [RFC1122] such that they accommodate current practice in processing TCP urgent indications, provides advice to applications using the urgent mechanism, and raises awareness about the @@ -133,23 +134,23 @@ to stimulate the receiving user to accept some "urgent data" and to permit the receiving TCP to indicate to the receiving user when all the currently known urgent data have been received by the user. The TCP urgent 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]. 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 - 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 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" data: the so-called "urgent data" should be delivered "in-line" to the TCP user. @@ -193,21 +194,21 @@ Unfortunately, virtually all TCP implementations process TCP urgent data differently. By default, the last byte of "urgent data" is delivered "out of band" to the application. That is, it is not 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 with the MSG_OOB flag set is issued. Most implementations provide a socket option (SO_OOBINLINE) that 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. 3.2. Semantics of the Urgent Pointer All the popular implementations that the authors of this document 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 when RFC 1122 officially updated RFC 793 to clarify the ambiguity in the semantics of the Urgent Pointer, this clarification was never reflected into actual implementations (i.e., virtually all @@ -284,21 +285,21 @@ As a result of the issues discussed in Section 3.2 and Section 3.4, new applications SHOULD NOT employ the TCP urgent mechanism. However, TCP implementations MUST still include support for the urgent mechanism such that existing applications can still use it. 6. Advice to applications that make use of the urgent mechanism 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" is delivered inline, as intended by the IETF specifications. 7. Security Considerations Given that there are two different interpretations of the semantics of the Urgent Pointer in current implementations (e.g., depending on the value of the tcp_stdurg sysctl), and that middle-boxes (such as packet scrubbers) or the end-systems themselves could cause the urgent data to be processed "in band", there exists ambiguity in how "urgent data" sent by a TCP will be processed by the intended @@ -419,35 +420,35 @@ Linux supports only one byte of urgent data. That is, only the byte preceding the Urgent Pointer is considered as "urgent data". A.3. NetBSD 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 sysctl to override this behavior. 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 MSG_OOB flag. NetBSD supports only one byte of urgent data. That is, only the byte preceding the Urgent Pointer is considered as "urgent data". A.4. OpenBSD OpenBSD 4.2 [OpenBSD] interprets the semantics of the urgent pointer as specified in Section 4 of this document. It does not provide any sysctl to override this behavior. 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. OpenBSD supports only one byte of urgent data. That is, only the byte preceding the Urgent Pointer is considered as "urgent data". A.5. Cisco IOS software 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 document. @@ -479,45 +480,50 @@ BSDUrgent system-wide variable to override this behavior, interpreting the Urgent Pointer as specified in RFC 1122 [RFC1122]. Windows 95 supports only one byte of urgent data. That is, only the byte preceding the Urgent Pointer is considered as "urgent data". [Windows95] Appendix B. Changes from previous versions of the draft (to be removed by the RFC Editor before publishing this document as an 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 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 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 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 Incorporated the specific changes/advice stated in http://www.ietf.org/mail-archive/web/tcpm/current/msg04548.html in 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 adopting the document as a tcpm wg item. Authors' Addresses Fernando Gont Universidad Tecnologica Nacional / Facultad Regional Haedo Evaristo Carriego 2644 Haedo, Provincia de Buenos Aires 1706