Adding Explicit Congestion Notification (ECN) Capability to TCP's SYN/ACK Packets

Metadata

Publisher: IETF
Doc Type: Experimental
Pages: 33
Abstract: The proposal in this document is Experimental. While it may be deployed in the current Internet, it does not represent a consensus that this is the best possible mechanism for the use of Explicit Congestion Notification (ECN) in TCP SYN/ACK packets. This document describes an optional, experimental modification to RFC 3168 to allow TCP SYN/ACK packets to be ECN-Capable. For TCP, RFC 3168 specifies setting an ECN-Capable codepoint on data packets, but not on SYN and SYN/ACK packets. However, because of the high cost to the TCP transfer of having a SYN/ACK packet dropped, with the resulting retransmission timeout, this document describes the use of ECN for the SYN/ACK packet itself, when sent in response to a SYN packet with the two ECN flags set in the TCP header, indicating a willingness to use ECN. Setting the initial TCP SYN/ACK packet as ECN-Capable can be of great benefit to the TCP connection, avoiding the severe penalty of a retransmission timeout for a connection that has not yet started placing a load on the network. The TCP responder (the sender of the SYN/ACK packet) must reply to a report of an ECN-marked SYN/ACK packet by resending a SYN/ACK packet that is not ECN-Capable. If the resent SYN/ACK packet is acknowledged, then the TCP responder reduces its initial congestion window from two, three, or four segments to one segment, thereby reducing the subsequent load from that connection on the network. If instead the SYN/ACK packet is dropped, or for some other reason the TCP responder does not receive an acknowledgement in the specified time, the TCP responder follows TCP standards for a dropped SYN/ACK packet (setting the retransmission timer). This memo defines an Experimental Protocol for the Internet community.
Publication Date: 2009-06-01
Status Note: Experimental
DOI: 10.17487/RFC5562
Link: https://doi.org/10.17487/RFC5562
Author(s): Aleksandar Kuzmanovic
Amit Mondal
Sally Floyd
Dr. K. K. Ramakrishnan
Keyword(s): ECN

Latest version of IETF RFC 5562

Document Versions — IETF RFC 5562

▶ IETF RFC 5562 (2009-06-01)

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Normative Reference(s)

IETF RFC 793 [Superseded*]
IETF RFC 2119 [Active*]
IETF RFC 2988 [Superseded*]
IETF RFC 3168 [Active*]

Bibliographic Reference(s)

IETF.draft-ietf-tcpm-ecnsyn-06 — L08 EXTERNAL
A. Kuzmanovic, The Power of Explicit Congestion Notification, SIGCOMM 2005. EXTERNAL
S. Athuraliya, V. H. Li, S. H. Low and Q. Yin, "REM: Active Queue Management", IEEE Network, May 2001. EXTERNAL
ECN-SYN web page with simulation scripts, http://www.icir.org/floyd/ecn-syn . EXTERNAL
Dax Kelson, "8% of the Internet unreachable!", September 10, 2000, email to the Linux kernel mailing list, http://lkml.indiana.edu/hypermail/linux/kernel/ 0009.1/0329.html . EXTERNAL
C. Hollot, V. Misra, W. Gong, and D. Towsley, "On Designing Improved Controllers for AQM Routers Supporting TCP Flows", April 1998. EXTERNAL
Dan J. Bernstein, SYN cookies, 1997, see also < http://cr.yp.to/syncookies.html >. EXTERNAL
M. Sridharan, D. Bansal, and D. Thaler, "Implementation Report on Experiences with Various TCP RFCs", Presentation in the TSVAREA, IETF 68, March 2007. http://www3.ietf.org/proceedings/07mar/slides/tsvarea- 3/sld6.htm . EXTERNAL
A. Medina, M. Allman, and S. Floyd, "Measuring the Evolution of Transport Protocols in the Internet", ACM CCR, April 2005. EXTERNAL
S. Floyd, "[BEHAVE] Response of firewalls and middleboxes to TCP SYN packets that are ECN-Capable?", August 2, 2007, email to the BEHAVE mailing list, http://www1.ietf.org/ mail-archive/web/behave/current/msg02644.html . EXTERNAL
S. Floyd, Ed., and E. Kohler, Ed., "Tools for the Evaluation of Simulation and Testbed Scenarios", Work in Progress, February 2008. EXTERNAL
F. Smith, F. Campos, K. Jeffay, and D. Ott, "What TCP/IP Protocol Headers Can Tell us about the Web", SIGMETRICS, June 2001. EXTERNAL
Floyd, S., and Jacobson, V., "Random Early Detection gateways for Congestion Avoidance", IEEE/ACM Transactions on Networking, V.1 N.4, August 1993. EXTERNAL
IETF RFC 2309 [Superseded*]
IETF RFC 2581 [Superseded*]
IETF RFC 3042 [Active*]
IETF RFC 3360 [Active*]
IETF RFC 3390 [Active*]
IETF RFC 4987 [Active*]

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doi: 10.17487/RFC5562
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<cite id="bib-rfc5562">IETF RFC 5562</cite>, Adding Explicit Congestion Notification (ECN) Capability to TCP&#x27;s SYN/ACK Packets
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Referenced By

IETF RFC 7141 [Active*]
IETF RFC 7414 [Active*]
IETF RFC 9768 [Active*]