draft-ietf-tcpm-tcp-rfc4614bis-01.txt   draft-ietf-tcpm-tcp-rfc4614bis-02.txt 
TCP Maintenance and Minor Extensions M. Duke TCP Maintenance and Minor Extensions M. Duke
(TCPM) WG F5 (TCPM) WG F5
Internet-Draft R. Braden Internet-Draft R. Braden
Obsoletes: 4614 (if approved) ISI Obsoletes: 4614 (if approved) ISI
Intended status: Informational W. Eddy Intended status: Informational W. Eddy
Expires: May 25, 2014 MTI Systems Expires: June 6, 2014 MTI Systems
E. Blanton E. Blanton
A. Zimmermann A. Zimmermann
NetApp, Inc. NetApp, Inc.
November 21, 2013 December 3, 2013
A Roadmap for Transmission Control Protocol (TCP) Specification A Roadmap for Transmission Control Protocol (TCP) Specification
Documents Documents
draft-ietf-tcpm-tcp-rfc4614bis-01 draft-ietf-tcpm-tcp-rfc4614bis-02
Abstract Abstract
This document contains a "roadmap" to the Requests for Comments (RFC) This document contains a "roadmap" to the Requests for Comments (RFC)
documents relating to the Internet's Transmission Control Protocol documents relating to the Internet's Transmission Control Protocol
(TCP). This roadmap provides a brief summary of the documents (TCP). This roadmap provides a brief summary of the documents
defining TCP and various TCP extensions that have accumulated in the defining TCP and various TCP extensions that have accumulated in the
RFC series. This serves as a guide and quick reference for both TCP RFC series. This serves as a guide and quick reference for both TCP
implementers and other parties who desire information contained in implementers and other parties who desire information contained in
the TCP-related RFCs. the TCP-related RFCs.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
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."
This Internet-Draft will expire on May 25, 2014. This Internet-Draft will expire on June 6, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2013 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
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4.2. Congestion Control Extensions . . . . . . . . . . . . . . 18 4.2. Congestion Control Extensions . . . . . . . . . . . . . . 18
4.3. Loss Recovery Extensions . . . . . . . . . . . . . . . . . 19 4.3. Loss Recovery Extensions . . . . . . . . . . . . . . . . . 19
4.4. Detection and Prevention of Spurious Retransmissions . . . 20 4.4. Detection and Prevention of Spurious Retransmissions . . . 20
4.5. Multipath TCP . . . . . . . . . . . . . . . . . . . . . . 21 4.5. Multipath TCP . . . . . . . . . . . . . . . . . . . . . . 21
5. TCP Parameters at IANA . . . . . . . . . . . . . . . . . . . . 21 5. TCP Parameters at IANA . . . . . . . . . . . . . . . . . . . . 21
6. Historic and Undeployed Extensions . . . . . . . . . . . . . . 22 6. Historic and Undeployed Extensions . . . . . . . . . . . . . . 22
7. Support Documents . . . . . . . . . . . . . . . . . . . . . . 25 7. Support Documents . . . . . . . . . . . . . . . . . . . . . . 25
7.1. Foundational Works . . . . . . . . . . . . . . . . . . . . 25 7.1. Foundational Works . . . . . . . . . . . . . . . . . . . . 25
7.2. Architectural Guidelines . . . . . . . . . . . . . . . . . 27 7.2. Architectural Guidelines . . . . . . . . . . . . . . . . . 27
7.3. Difficult Network Environments . . . . . . . . . . . . . . 28 7.3. Difficult Network Environments . . . . . . . . . . . . . . 28
7.4. Guidance for Developing, Analyzing, and Evaluating TCP . . 30 7.4. Guidance for Developing, Analyzing, and Evaluating TCP . . 31
7.5. Implementation Advice . . . . . . . . . . . . . . . . . . 31 7.5. Implementation Advice . . . . . . . . . . . . . . . . . . 32
7.6. Tools and Tutorials . . . . . . . . . . . . . . . . . . . 34 7.6. Tools and Tutorials . . . . . . . . . . . . . . . . . . . 34
7.7. Management Information Bases . . . . . . . . . . . . . . . 34 7.7. Management Information Bases . . . . . . . . . . . . . . . 35
7.8. Case Studies . . . . . . . . . . . . . . . . . . . . . . . 36 7.8. Case Studies . . . . . . . . . . . . . . . . . . . . . . . 36
8. Undocumented TCP Features . . . . . . . . . . . . . . . . . . 37 8. Undocumented TCP Features . . . . . . . . . . . . . . . . . . 37
9. Security Considerations . . . . . . . . . . . . . . . . . . . 38 9. Security Considerations . . . . . . . . . . . . . . . . . . . 39
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 39 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 39
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 39 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 39
12.1. Normative References . . . . . . . . . . . . . . . . . . . 39 12.1. Normative References . . . . . . . . . . . . . . . . . . . 39
12.2. Informative References . . . . . . . . . . . . . . . . . . 48 12.2. Informative References . . . . . . . . . . . . . . . . . . 49
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 50 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 50
1. Introduction 1. Introduction
A correct and efficient implementation of the Transmission Control A correct and efficient implementation of the Transmission Control
Protocol (TCP) is a critical part of the software of most Internet Protocol (TCP) is a critical part of the software of most Internet
hosts. As TCP has evolved over the years, many distinct documents hosts. As TCP has evolved over the years, many distinct documents
have become part of the accepted standard for TCP. At the same time, have become part of the accepted standard for TCP. At the same time,
a large number of experimental modifications to TCP have also been a large number of experimental modifications to TCP have also been
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studies, and other advice. studies, and other advice.
As an introduction to newcomers and an attempt to organize the As an introduction to newcomers and an attempt to organize the
plethora of information for old hands, this document contains a plethora of information for old hands, this document contains a
"roadmap" to the TCP-related RFCs. It provides a brief summary of "roadmap" to the TCP-related RFCs. It provides a brief summary of
the RFC documents that define TCP. This should provide guidance to the RFC documents that define TCP. This should provide guidance to
implementers on the relevance and significance of the standards-track implementers on the relevance and significance of the standards-track
extensions, informational notes, and best current practices that extensions, informational notes, and best current practices that
relate to TCP. relate to TCP.
This document is not an update of RFC 1122 and is not a rigorous This document is not an update of RFC 1122 [RFC1122] and is not a
standard for what needs to be implemented in TCP. This document is rigorous standard for what needs to be implemented in TCP. This
merely an informational roadmap that captures, organizes, and document is merely an informational roadmap that captures, organizes,
summarizes most of the RFC documents that a TCP implementer, and summarizes most of the RFC documents that a TCP implementer,
experimenter, or student should be aware of. Particular comments or experimenter, or student should be aware of. Particular comments or
broad categorizations that this document makes about individual broad categorizations that this document makes about individual
mechanisms and behaviors are not to be taken as definitive, nor mechanisms and behaviors are not to be taken as definitive, nor
should the content of this document alone influence implementation should the content of this document alone influence implementation
decisions. decisions.
This roadmap includes a brief description of the contents of each This roadmap includes a brief description of the contents of each
TCP-related RFC. In some cases, we simply supply the abstract or a TCP-related RFC. In some cases, we simply supply the abstract or a
key summary sentence from the text as a terse description. In key summary sentence from the text as a terse description. In
addition, a letter code after an RFC number indicates its category in addition, a letter code after an RFC number indicates its category in
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I - Informational I - Informational
H - Historic H - Historic
B - Best Current Practice B - Best Current Practice
U - Unknown (not formally defined) U - Unknown (not formally defined)
Note that the category of an RFC does not necessarily reflect its Note that the category of an RFC does not necessarily reflect its
current relevance. For instance, RFC 5681 is nearly universally current relevance. For instance, RFC 5681 [RFC5681] is considered
deployed although it is only a Draft Standard. Similarly, some part of the required core functionality of TCP, although the RFC is
Informational RFCs contain significant technical proposals for only a Draft Standard. Similarly, some Informational RFCs contain
changing TCP. significant technical proposals for changing TCP.
Finally, if an error in the technical content has been found after Finally, if an error in the technical content has been found after
publication of an RFC, this fact is indicated by the term "(Errata)" publication of an RFC, this fact is indicated by the term "(Errata)"
in the headline of the RFC's description. The contents of the errata in the headline of the RFC's description. The contents of the errata
can be found at the RFC editor home page [Errata]. can be found at the RFC editor home page [Errata].
This roadmap is divided into three main sections. Section 2 lists This roadmap is divided into three main sections. Section 2 lists
the RFCs that describe absolutely required TCP behaviors for proper the RFCs that describe absolutely required TCP behaviors for proper
functioning and interoperability. Further RFCs that describe functioning and interoperability. Further RFCs that describe
strongly encouraged, but non-essential, behaviors are listed in strongly encouraged, but non-essential, behaviors are listed in
Section 3. Experimental extensions that are not yet standard Section 3. Experimental extensions that are not yet standard
practices, but that potentially could be in the future, are described practices, but that potentially could be in the future, are described
in Section 4. in Section 4.
The reader will probably notice that these three sections are broadly The reader will probably notice that these three sections are broadly
equivalent to MUST/SHOULD/MAY specifications (per RFC 2119), and equivalent to MUST/SHOULD/MAY specifications (per RFC 2119
although the authors support this intuition, this document is merely [RFC2119]), and although the authors support this intuition, this
descriptive; it does not represent a binding standards-track document is merely descriptive; it does not represent a binding
position. Individual implementers still need to examine the standards-track position. Individual implementers still need to
standards documents themselves to evaluate specific requirement examine the standards documents themselves to evaluate specific
levels. requirement levels.
Section 5 describes both the procedures that the Internet Assigned Section 5 describes both the procedures that the Internet Assigned
Numbers Authority (IANA) uses and an RFC author should follow when Numbers Authority (IANA) uses and an RFC author should follow when
new TCP parameters are requested and finally assigned. new TCP parameters are requested and finally assigned.
A small number of older experimental extensions that have not been A small number of older experimental extensions that have not been
widely implemented, deployed, and used are noted in Section 6. Many widely implemented, deployed, and used are noted in Section 6. Many
other supporting documents that are relevant to the development, other supporting documents that are relevant to the development,
implementation, and deployment of TCP are described in Section 7. implementation, and deployment of TCP are described in Section 7.
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(Errata) (Errata)
This is the fundamental TCP specification document [RFC0793]. This is the fundamental TCP specification document [RFC0793].
Written by Jon Postel as part of the Internet protocol suite's Written by Jon Postel as part of the Internet protocol suite's
core, it describes the TCP packet format, the TCP state machine core, it describes the TCP packet format, the TCP state machine
and event processing, and TCP's semantics for data transmission, and event processing, and TCP's semantics for data transmission,
reliability, flow control, multiplexing, and acknowledgment. reliability, flow control, multiplexing, and acknowledgment.
Section 3.6 of RFC 793, describing TCP's handling of the IP Section 3.6 of RFC 793, describing TCP's handling of the IP
precedence and security compartment, is mostly irrelevant today. precedence and security compartment, is mostly irrelevant today.
RFC 2873 changed the IP precedence handling, and the security RFC 2873 (see Section 2) changed the IP precedence handling, and
compartment portion of the API is no longer implemented or used. the security compartment portion of the API is no longer
In addition, RFC 793 did not describe any congestion control implemented or used. In addition, RFC 793 did not describe any
mechanism. Otherwise, however, the majority of this document congestion control mechanism. Otherwise, however, the majority of
still accurately describes modern TCPs. RFC 793 is the last of a this document still accurately describes modern TCPs. RFC 793 is
series of developmental TCP specifications, starting in the the last of a series of developmental TCP specifications, starting
Internet Experimental Notes (IENs) and continuing in the RFC in the Internet Experimental Notes (IENs) and continuing in the
series. RFC series.
RFC 1122 S: "Requirements for Internet Hosts - Communication Layers" RFC 1122 S: "Requirements for Internet Hosts - Communication Layers"
(October 1989) (October 1989)
This document [RFC1122] updates and clarifies RFC 793, fixing some This document [RFC1122] updates and clarifies RFC 793 (see
specification bugs and oversights. It also explains some features Section 2), fixing some specification bugs and oversights. It
such as keep-alives and Karn's and Jacobson's RTO estimation also explains some features such as keep-alives and Karn's and
algorithms [KP87][Jac88][JK92]. ICMP interactions are mentioned, Jacobson's RTO estimation algorithms [KP87][Jac88][JK92]. ICMP
and some tips are given for efficient implementation. RFC 1122 is interactions are mentioned, and some tips are given for efficient
an Applicability Statement, listing the various features that implementation. RFC 1122 is an Applicability Statement, listing
MUST, SHOULD, MAY, SHOULD NOT, and MUST NOT be present in the various features that MUST, SHOULD, MAY, SHOULD NOT, and MUST
standards-conforming TCP implementations. Unlike a purely NOT be present in standards-conforming TCP implementations.
informational "roadmap", this Applicability Statement is a Unlike a purely informational "roadmap", this Applicability
standards document and gives formal rules for implementation. Statement is a standards document and gives formal rules for
implementation.
RFC 2460 S: "Internet Protocol, Version 6 (IPv6) Specification" RFC 2460 S: "Internet Protocol, Version 6 (IPv6) Specification"
(December 1998) (Errata) (December 1998) (Errata)
This document [RFC2460] is of relevance to TCP because it defines This document [RFC2460] is of relevance to TCP because it defines
how the pseudo-header for TCP's checksum computation is derived how the pseudo-header for TCP's checksum computation is derived
when 128-bit IPv6 addresses are used instead of 32-bit IPv4 when 128-bit IPv6 addresses are used instead of 32-bit IPv4
addresses. Additionally, RFC 2675 describes TCP changes required addresses. Additionally, RFC 2675 (see Section 3.1) describes TCP
to support IPv6 jumbograms. changes required to support IPv6 jumbograms.
RFC 2873 S: "TCP Processing of the IPv4 Precedence Field" (June 2000) RFC 2873 S: "TCP Processing of the IPv4 Precedence Field" (June 2000)
(Errata) (Errata)
This document [RFC2873] removes from the TCP specification all This document [RFC2873] removes from the TCP specification all
processing of the precedence bits of the TOS byte of the IP processing of the precedence bits of the TOS byte of the IP
header. This resolves a conflict over the use of these bits header. This resolves a conflict over the use of these bits
between RFC 793 and Differentiated Services [RFC2474]. between RFC 793 Section 2 and Differentiated Services [RFC2474].
RFC 5681 S: "TCP Congestion Control" (August 2009) RFC 5681 S: "TCP Congestion Control" (August 2009)
Although RFC 793 did not contain any congestion control Although RFC 793 (see Section 2) did not contain any congestion
mechanisms, today congestion control is a required component of control mechanisms, today congestion control is a required
TCP implementations. This document [RFC5681] defines the current component of TCP implementations. This document [RFC5681] defines
versions of Van Jacobson's congestion avoidance and control the current versions of Van Jacobson's congestion avoidance and
mechanisms for TCP, based on his 1988 SIGCOMM paper [Jac88]. control mechanisms for TCP, based on his 1988 SIGCOMM paper
[Jac88].
A number of behaviors that together constitute what the community A number of behaviors that together constitute what the community
refers to as "Reno TCP" are described in RFC 5681. The name refers to as "Reno TCP" are described in RFC 5681. The name
"Reno" comes from the Net/2 release of the 4.3 BSD operating "Reno" comes from the Net/2 release of the 4.3 BSD operating
system. This is generally regarded as the least common system. This is generally regarded as the least common
denominator among TCP flavors currently found running on Internet denominator among TCP flavors currently found running on Internet
hosts. Reno TCP includes the congestion control features of slow hosts. Reno TCP includes the congestion control features of slow
start, congestion avoidance, fast retransmit, and fast recovery. start, congestion avoidance, fast retransmit, and fast recovery.
RFC 1122 [RFC1122] mandates the implementation of a congestion RFC 5681 details the currently accepted congestion control
control mechanism, and RFC 5681 [RFC5681] details the currently mechanism, while RFC 1122 Section 2 mandates that such a
accepted mechanism. RFC 5681 differs slightly from the other congestion control mechanism must be implemented. RFC 5681
documents listed in this section, as it does not affect the differs slightly from the other documents listed in this section,
ability of two TCP endpoints to communicate; however, congestion as it does not affect the ability of two TCP endpoints to
control remains a critical component of any widely deployed TCP communicate; however, congestion control remains a critical
implementation and is required for the avoidance of congestion component of any widely deployed TCP implementation and is
collapse and to ensure fairness among competing flows. required for the avoidance of congestion collapse and to ensure
fairness among competing flows.
RFC 2001 and RFC 2581 are the conceptual precursors of RFC 5681. RFC 2001 and RFC 2581 are the conceptual precursors of RFC 5681.
The most important changes relative to RFC 2581 are: The most important changes relative to RFC 2581 are:
(a) The initial window requirements were changed to allow larger (a) The initial window requirements were changed to allow larger
Initial Windows as standardized in [RFC3390]. Initial Windows as standardized in [RFC3390] (see
Section 3.2).
(b) During slow start and congestion avoidance, the usage of (b) During slow start and congestion avoidance, the usage of
Appropriate Byte Counting [RFC3465] is explicitly Appropriate Byte Counting [RFC3465] (see Section 3.2) is
recommended. explicitly recommended.
(c) The use of Limited Transmit [RFC3042] is now recommended. (c) The use of Limited Transmit [RFC3042] (see Section 3.3) is
now recommended.
RFC 6093 S: "On the Implementation of the TCP Urgent Mechanism" RFC 6093 S: "On the Implementation of the TCP Urgent Mechanism"
(January 2011) (January 2011)
This document [RFC6093] analyzes how current TCP stacks process This document [RFC6093] analyzes how current TCP stacks process
TCP urgent indications, and how the behavior of widely deployed TCP urgent indications, and how the behavior of widely deployed
middleboxes affects the urgent indications processing. The middleboxes affects the urgent indications processing. The
document updates the relevant specifications such that it document updates the relevant specifications such that it
accommodates current practice in processing TCP urgent accommodates current practice in processing TCP urgent
indications. Finally, the document raises awareness about the indications. Finally, the document raises awareness about the
reliability of TCP urgent indications in the Internet, and reliability of TCP urgent indications in the Internet, and
recommends against the use of urgent mechanism. recommends against the use of urgent mechanism.
RFC 6298 S: "Computing TCP's Retransmission Timer" (June 2011) RFC 6298 S: "Computing TCP's Retransmission Timer" (June 2011)
Abstract: "This document defines the standard algorithm that Abstract: "This document defines the standard algorithm that
Transmission Control Protocol (TCP) senders are required to use to Transmission Control Protocol (TCP) senders are required to use to
compute and manage their retransmission timer. It expands on the compute and manage their retransmission timer. It expands on the
discussion in section 4.2.3.1 of RFC 1122 and upgrades the discussion in section 4.2.3.1 of RFC 1122 (see Section 2) and
requirement of supporting the algorithm from a SHOULD to a MUST." upgrades the requirement of supporting the algorithm from a SHOULD
[RFC6298]. RFC 6298 updates RFC 2988 by changing the initial RTO to a MUST." [RFC6298]. RFC 6298 updates RFC 2988 by changing the
from 3s to 1s initial RTO from 3s to 1s
RFC 6691 I: "TCP Options and Maximum Segment Size (MSS)" (July 2012) RFC 6691 I: "TCP Options and Maximum Segment Size (MSS)" (July 2012)
This document [RFC6691] clarifies what value to use with the TCP This document [RFC6691] clarifies what value to use with the TCP
Maximum Segment Size (MSS) option when IP and TCP options are in Maximum Segment Size (MSS) option when IP and TCP options are in
use. use.
3. Recommended Enhancements 3. Recommended Enhancements
This section describes recommended TCP modifications that improve This section describes recommended TCP modifications that improve
performance and security. Section 3.1 represents fundamental changes performance and security. Section 3.1 represents fundamental changes
to the protocol. Section 3.2 and Section 3.3 list improvements over to the protocol. Section 3.2 and Section 3.3 list improvements over
the congestion control and loss recovery mechanisms as specified in the congestion control and loss recovery mechanisms as specified in
RFC 5681. Section 3.4 describes algorithms that allow a TCP sender RFC 5681 (see Section 2). Section 3.4 describes algorithms that
to detect whether it has entered loss recovery spuriously. allow a TCP sender to detect whether it has entered loss recovery
Section 3.5 lists documents that revolve around the various TCP spuriously. Section 3.5 lists documents that revolve around the
timers. Section 3.6 comprises Path MTU Discovery mechanisms. various TCP timers. Section 3.6 comprises Path MTU Discovery
Schemes for TCP/IP header compression are listed in Section 3.7. mechanisms. Schemes for TCP/IP header compression are listed in
Finally, Section 3.8 deals with the problem of preventing preventing Section 3.7. Finally, Section 3.8 deals with the problem of
acceptance of forged segments and flooding attacks. preventing preventing acceptance of forged segments and flooding
attacks.
3.1. Fundamental Changes 3.1. Fundamental Changes
RFC 1323 allows better utilization of high bandwidth-delay product RFC 1323 allows better utilization of high bandwidth-delay product
paths by providing some needed mechanisms for high-rate transfers. paths by providing some needed mechanisms for high-rate transfers.
RFC 2675 describes changes to TCP's semantic for using IPv6 RFC 2675 describes changes to TCP's semantic for using IPv6
Jumbograms. jumbograms.
RFC 1323 S: "TCP Extensions for High Performance" (May 1992) RFC 1323 S: "TCP Extensions for High Performance" (May 1992)
This document [RFC1323] defines TCP extensions for window scaling, This document [RFC1323] defines TCP extensions for window scaling,
timestamps, and protection against wrapped sequence numbers, for timestamps, and protection against wrapped sequence numbers, for
efficient and safe operation over paths with large bandwidth-delay efficient and safe operation over paths with large bandwidth-delay
products. These extensions are commonly found in currently used products. These extensions are commonly found in currently used
systems; however, they may require manual tuning and systems; however, they may require manual tuning and
configuration. One issue in this specification that is still configuration. One issue in this specification that is still
under discussion concerns a modification to the algorithm for under discussion concerns a modification to the algorithm for
estimating the mean RTT when timestamps are used. RFC 1072 and estimating the mean RTT when timestamps are used. RFC 1072 and
RFC 1185 are the conceptual precursors of RFC 1323. RFC 1185 are the conceptual precursors of RFC 1323.
RFC 2675 S: "IPv6 Jumbograms" (August 1999) (Errata) RFC 2675 S: "IPv6 Jumbograms" (August 1999) (Errata)
IPv6 supports longer datagrams than were allowed in IPv4. These IPv6 supports longer datagrams than were allowed in IPv4. These
are known as Jumbograms, and use with TCP has necessitated changes are known as jumbograms, and use with TCP has necessitated changes
to the handling of TCP's MSS and Urgent fields (both 16 bits). to the handling of TCP's MSS and Urgent fields (both 16 bits).
This document [RFC2675] explains those changes. Although it This document [RFC2675] explains those changes. Although it
describes changes to basic header semantics, these changes should describes changes to basic header semantics, these changes should
only affect the use of very large segments, such as IPv6 only affect the use of very large segments, such as IPv6
jumbograms, which are currently rarely used in the general jumbograms, which are currently rarely used in the general
Internet. Internet.
Supporting the behavior described in this document does not affect Supporting the behavior described in this document does not affect
interoperability with other TCP implementations when IPv4 or non- interoperability with other TCP implementations when IPv4 or non-
jumbogram IPv6 is used. This document states that jumbograms are jumbogram IPv6 is used. This document states that jumbograms are
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nodes, including each router in the end-to-end path, will support nodes, including each router in the end-to-end path, will support
jumbograms. If even a single node that does not support jumbograms. If even a single node that does not support
jumbograms is attached to a local network, then no host on that jumbograms is attached to a local network, then no host on that
network may use jumbograms. This explains why jumbogram use has network may use jumbograms. This explains why jumbogram use has
been rare, and why this document is considered a performance been rare, and why this document is considered a performance
optimization and not part of TCP over IPv6's basic functionality. optimization and not part of TCP over IPv6's basic functionality.
3.2. Congestion Control Extensions 3.2. Congestion Control Extensions
Two of the most important aspects of TCP are its congestion control Two of the most important aspects of TCP are its congestion control
and loss recovery features. TCP traditionally treats lost packets as and loss recovery features. TCP treats lost packets as indicating
indicating congestion-related loss, and cannot distinguish between congestion-related loss, and cannot distinguish between congestion-
congestion-related loss and loss due to transmission errors. Even related loss and loss due to transmission errors. Even when ECN is
when ECN is in use, there is a rather intimate coupling between in use, there is a rather intimate coupling between congestion
congestion control and loss recovery mechanisms. There are several control and loss recovery mechanisms. There are several extensions
extensions to both features, and more often than not, a particular to both features, and more often than not, a particular extension
extension applies to both. In this two sub-sections, we group applies to both. In this two sub-sections, we group enhancements to
enhancements to TCP's congestion control, while the next sub-section TCP's congestion control, while the next sub-section focus on TCP's
focus on TCP's loss recovery. loss recovery.
RFC 3168 S: "The Addition of Explicit Congestion Notification (ECN) RFC 3168 S: "The Addition of Explicit Congestion Notification (ECN)
to IP" (September 2001) to IP" (September 2001)
This document [RFC3168] defines a means for end hosts to detect This document [RFC3168] defines a means for end hosts to detect
congestion before congested routers are forced to discard packets. congestion before congested routers are forced to discard packets.
Although congestion notification takes place at the IP level, ECN Although congestion notification takes place at the IP level, ECN
requires support at the transport level (e.g., in TCP) to echo the requires support at the transport level (e.g., in TCP) to echo the
bits and adapt the sending rate. This document updates RFC 793 to bits and adapt the sending rate. This document updates RFC 793
define two previously unused flag bits in the TCP header for ECN (see Section 2) to define two previously unused flag bits in the
support. RFC 3540 provides a supplementary (experimental) means TCP header for ECN support. RFC 3540 (see Section 4.2) provides a
for more secure use of ECN, and RFC 2884 provides some sample supplementary (experimental) means for more secure use of ECN, and
results from using ECN. RFC 2884 (see Section 7.8) provides some sample results from using
ECN.
RFC 3390 S: "Increasing TCP's Initial Window" (October 2002)
This document [RFC3390] specifies an increase in the permitted
initial window for TCP from one segment to three or four segments
during the slow start phase, depending on the segment size.
RFC 3465 E: "TCP Congestion Control with Appropriate Byte Counting RFC 3465 E: "TCP Congestion Control with Appropriate Byte Counting
(ABC)" (February 2003) (ABC)" (February 2003)
This document [RFC3465] suggests that congestion control use the This document [RFC3465] suggests that congestion control use the
number of bytes acknowledged instead of the number of number of bytes acknowledged instead of the number of
acknowledgments received. The ABC mechanism behaves differently acknowledgments received. The ABC mechanism behaves differently
than the standard method when there is not a one-to-one than the standard method when there is not a one-to-one
relationship between data segments and acknowledgments. ABC still relationship between data segments and acknowledgments. ABC still
operates within the accepted guidelines, but is more robust to operates within the accepted guidelines, but is more robust to
delayed ACKs and ACK-division [SCWA99][RFC3449]. [RFC3465] is delayed ACKs and ACK-division [SCWA99][RFC3449]. ABC is
recommended by [RFC5681]. recommended by RFC 5681 (see Section 2).
RFC 3390 S: "Increasing TCP's Initial Window" (October 2002)
This document [RFC3390] specifies an increase in the permitted
initial window for TCP from one segment to three or four segments
during the slow start phase, depending on the segment size.
RFC 6633 S: "Deprecation of ICMP Source Quench Messages" (May 2012) RFC 6633 S: "Deprecation of ICMP Source Quench Messages" (May 2012)
This document [RFC6633] formally deprecates the use of ICMP Source This document [RFC6633] formally deprecates the use of ICMP Source
Quench messages by transport protocols and provides a Quench messages by transport protocols and recommends against the
recommendation against the implementation of [RFC1016]. implementation of [RFC1016].
3.3. Loss Recovery Extensions 3.3. Loss Recovery Extensions
For the typical implementation of the TCP fast recovery algorithm For the typical implementation of the TCP fast recovery algorithm
described in [RFC5681], a TCP sender only retransmits a segment after described in RFC 5681 (see Section 2), a TCP sender only retransmits
a retransmit timeout has occurred, or after three duplicate ACKs have a segment after a retransmit timeout has occurred, or after three
arrived triggering the fast retransmit. A single RTO might result in duplicate ACKs have arrived triggering the fast retransmit. A single
the retransmission of several segments, while the fast retransmit RTO might result in the retransmission of several segments, while the
algorithm in RFC 5681 leads only to a single retransmission. Hence, fast retransmit algorithm in RFC 5681 leads only to a single
multiple losses from a single window of data can lead to a retransmission. Hence, multiple losses from a single window of data
performance degradation. Documents listed in this section aim to can lead to a performance degradation. Documents listed in this
improve the overall performance of TCP's standard loss recovery section aim to improve the overall performance of TCP's standard loss
algorithms. In particular, some of them allows TCP senders to recovery algorithms. In particular, some of them allows TCP senders
recover more effectively when multiple segments are lost from a to recover more effectively when multiple segments are lost from a
single flight of data. single flight of data.
RFC 2018 S: "TCP Selective Acknowledgment Options" (October 1996) RFC 2018 S: "TCP Selective Acknowledgment Options" (October 1996)
(Errata) (Errata)
When more than one packet is lost during one round trip time TCP When more than one packet is lost during one round trip time TCP
may experience poor performance since a TCP sender can only learn may experience poor performance since a TCP sender can only learn
about a single lost packet per round trip time from cumulative about a single lost packet per round trip time from cumulative
acknowledgments. This document [RFC2018] defines the basic acknowledgments. This document [RFC2018] defines the basic
selective acknowledgment (SACK) mechanism for TCP, which can help selective acknowledgment (SACK) mechanism for TCP, which can help
skipping to change at page 11, line 29 skipping to change at page 11, line 32
RFC 3042 S: "Enhancing TCP's Loss Recovery Using Limited Transmit" RFC 3042 S: "Enhancing TCP's Loss Recovery Using Limited Transmit"
(January 2001) (January 2001)
Abstract: "This document proposes Limited Transmit, a new Abstract: "This document proposes Limited Transmit, a new
Transmission Control Protocol (TCP) mechanism that can be used to Transmission Control Protocol (TCP) mechanism that can be used to
more effectively recover lost segments when a connection's more effectively recover lost segments when a connection's
congestion window is small, or when a large number of segments are congestion window is small, or when a large number of segments are
lost in a single transmission window." [RFC3042] Tests from 2004 lost in a single transmission window." [RFC3042] Tests from 2004
showed that Limited Transmit was deployed in roughly one third of showed that Limited Transmit was deployed in roughly one third of
the web servers tested [MAF04]. [RFC3042] is recommended by the web servers tested [MAF04]. Limited Transmit is recommended
[RFC5681]. by RFC 5681 (see Section 2).
RFC 6582 S: "The NewReno Modification to TCP's Fast Recovery RFC 6582 S: "The NewReno Modification to TCP's Fast Recovery
Algorithm" (April 2012) Algorithm" (April 2012)
This document [RFC6582] specifies a modification to the standard This document [RFC6582] specifies a modification to the standard
Reno fast recovery algorithm, whereby a TCP sender can use partial Reno fast recovery algorithm, whereby a TCP sender can use partial
acknowledgments to make inferences determining the next segment to acknowledgments to make inferences determining the next segment to
send in situations where SACK would be helpful but isn't send in situations where SACK would be helpful but isn't
available. Although it is only a slight modification, the NewReno available. Although it is only a slight modification, the NewReno
behavior can make a significant difference in performance when behavior can make a significant difference in performance when
skipping to change at page 12, line 10 skipping to change at page 12, line 11
algorithms and advance those two algorithms from Experimental to algorithms and advance those two algorithms from Experimental to
Standards Track status. The main change in RFC 6582 relative to Standards Track status. The main change in RFC 6582 relative to
RFC 3782 was to solve a performance degradation that could occur RFC 3782 was to solve a performance degradation that could occur
if FlightSize on Full ACK reception is zero. if FlightSize on Full ACK reception is zero.
RFC 6675 S: "A Conservative Loss Recovery Algorithm Based on RFC 6675 S: "A Conservative Loss Recovery Algorithm Based on
Selective Acknowledgment (SACK) for TCP" (August 2012) Selective Acknowledgment (SACK) for TCP" (August 2012)
This document [RFC6675] describes a conservative loss recovery This document [RFC6675] describes a conservative loss recovery
algorithm for TCP that is based on the use of the selective algorithm for TCP that is based on the use of the selective
acknowledgment (SACK) TCP option [RFC2018]. The algorithm acknowledgment (SACK) TCP option [RFC2018] (see Section 3.3). The
conforms to the spirit of the congestion control specification in algorithm conforms to the spirit of the congestion control
RFC 5681, but allows TCP senders to recover more effectively when specification in RFC 5681 (see Section 2), but allows TCP senders
multiple segments are lost from a single flight of data. to recover more effectively when multiple segments are lost from a
single flight of data.
RFC 6675 is a revision of RFC 3517 to address several situations RFC 6675 is a revision of RFC 3517 to address several situations
that are not handled explicitly before. In particular that are not handled explicitly before. In particular
(a) it improves the loss detection in the event that the sender (a) it improves the loss detection in the event that the sender
has outstanding segments that are smaller than SMSS. has outstanding segments that are smaller than SMSS.
(b) it modifies the definition of a "duplicate acknowledgment" to (b) it modifies the definition of a "duplicate acknowledgment" to
utilize the SACK information in detecting loss. utilize the SACK information in detecting loss.
(c) it maintains the ACK clock under certain circumstances (c) it maintains the ACK clock under certain circumstances
involving loss at the end of the window. involving loss at the end of the window.
skipping to change at page 12, line 38 skipping to change at page 12, line 40
retransmissions have occurred, and then responding differently in retransmissions have occurred, and then responding differently in
order to recover performance. The IETF defined multiple algorithms order to recover performance. The IETF defined multiple algorithms
because there are tradeoffs in whether or not certain TCP options because there are tradeoffs in whether or not certain TCP options
need to be implemented, and concerns about IPR status. The Standards need to be implemented, and concerns about IPR status. The Standards
Track documents in this section are closely related to the Track documents in this section are closely related to the
Experimental documents in Section 4.4 also addressing this topic. Experimental documents in Section 4.4 also addressing this topic.
RFC 2883 S: "An Extension to the Selective Acknowledgement (SACK) RFC 2883 S: "An Extension to the Selective Acknowledgement (SACK)
Option for TCP" (July 2000) Option for TCP" (July 2000)
This document [RFC2883] extends RFC 2018. It enables use of the This document [RFC2883] extends RFC 2018 (see Section 3.3). It
SACK option to acknowledge duplicate packets. With this enables use of the SACK option to acknowledge duplicate packets.
extension, called DSACK, the sender is able to infer the order of With this extension, called DSACK, the sender is able to infer the
packets received at the receiver, and therefore to infer when it order of packets received at the receiver, and therefore to infer
has unnecessarily retransmitted a packet. when it has unnecessarily retransmitted a packet. A TCP sender
could then use this information to detect spurious retransmissions
(see [RFC3708].
RFC 4015 S: "The Eifel Response Algorithm for TCP" (February 2005) RFC 4015 S: "The Eifel Response Algorithm for TCP" (February 2005)
This document [RFC4015] describes the response portion of the This document [RFC4015] describes the response portion of the
Eifel algorithm, which can be used in conjunction with one of Eifel algorithm, which can be used in conjunction with one of
several methods of detecting when loss recovery has been several methods of detecting when loss recovery has been
spuriously entered, such as the Eifel detection algorithm in RFC spuriously entered, such as the Eifel detection algorithm in RFC
3522, the algorithm in RFC 3708, or F-RTO in RFC 5682. 3522 (see Section 4.4), the algorithm in RFC 3708 (see
Section 4.4), or F-RTO in RFC 5682 (see Section 3.4).
Abstract: "Based on an appropriate detection algorithm, the Eifel Abstract: "Based on an appropriate detection algorithm, the Eifel
response algorithm provides a way for a TCP sender to respond to a response algorithm provides a way for a TCP sender to respond to a
detected spurious timeout. It adapts the retransmission timer to detected spurious timeout. It adapts the retransmission timer to
avoid further spurious timeouts, and can avoid - depending on the avoid further spurious timeouts, and can avoid - depending on the
detection algorithm - the often unnecessary go-back-N retransmits detection algorithm - the often unnecessary go-back-N retransmits
that would otherwise be sent. In addition, the Eifel response that would otherwise be sent. In addition, the Eifel response
algorithm restores the congestion control state in such a way that algorithm restores the congestion control state in such a way that
packet bursts are avoided." packet bursts are avoided."
RFC 5682 S: "Forward RTO-Recovery (F-RTO): An Algorithm for Detecting RFC 5682 S: "Forward RTO-Recovery (F-RTO): An Algorithm for Detecting
Spurious Retransmission Timeouts with TCP" (September 2009) Spurious Retransmission Timeouts with TCP" (September 2009)
The F-RTO detection algorithm [RFC5682], originally described in The F-RTO detection algorithm [RFC5682], originally described in
RFC 4138, provides an option for inferring spurious retransmission RFC 4138, provides an option for inferring spurious retransmission
timeouts. Unlike some similar detection methods (e.g. RFC 3522 timeouts. Unlike some similar detection methods (e.g. RFC 3522
and RFC 3708), F-RTO does not rely on the use of any TCP options. in Section 4.4 and RFC 3708 in Section 4.4), F-RTO does not rely
The basic idea is to send previously unsent data after the first on the use of any TCP options. The basic idea is to send
retransmission after a RTO. If the ACKs advance the window, the previously unsent data after the first retransmission after a RTO.
RTO may be declared spurious. If the ACKs advance the window, the RTO may be declared spurious.
3.5. TCP Timeouts 3.5. TCP Timeouts
FIXME
RFC 5482 S: "TCP User Timeout Option" (June 2009) RFC 5482 S: "TCP User Timeout Option" (June 2009)
As a local per-connection parameter the TCP user timeout controls As a local per-connection parameter the TCP user timeout controls
how long transmitted data may remain unacknowledged before a how long transmitted data may remain unacknowledged before a
connection is forcefully closed. This document [RFC5482] connection is forcefully closed. This document [RFC5482]
specifies the TCP User Timeout Option that allows one end of a TCP specifies the TCP User Timeout Option that allows one end of a TCP
connection to advertise its current user timeout value. This connection to advertise its current user timeout value. This
information provides advice to the other end of the TCP connection information provides advice to the other end of the TCP connection
to adapt its user timeout accordingly. to adapt its user timeout accordingly.
skipping to change at page 14, line 19 skipping to change at page 14, line 19
small change to the way routers generate one type of ICMP message. small change to the way routers generate one type of ICMP message.
For a path that passes through a router that has not been so For a path that passes through a router that has not been so
changed, this technique might not discover the correct path MTU, changed, this technique might not discover the correct path MTU,
but it will always choose a path MTU as accurate as, and in many but it will always choose a path MTU as accurate as, and in many
cases more accurate than, the path MTU that would be chosen by cases more accurate than, the path MTU that would be chosen by
current practice." [RFC1191] current practice." [RFC1191]
RFC 1981 S: "Path MTU Discovery for IP version 6" (August 1996) RFC 1981 S: "Path MTU Discovery for IP version 6" (August 1996)
Abstract: "This document describes Path MTU Discovery for IP Abstract: "This document describes Path MTU Discovery for IP
version 6. It is largely derived from RFC 1191, which describes version 6. It is largely derived from RFC 1191 (see Section 3.6),
Path MTU Discovery for IP version 4." [RFC1981] which describes Path MTU Discovery for IP version 4." [RFC1981]
RFC 4821 S: "Packetization Layer Path MTU Discovery" (March 2007) RFC 4821 S: "Packetization Layer Path MTU Discovery" (March 2007)
Abstract: "This document describes a robust method for Path MTU Abstract: "This document describes a robust method for Path MTU
Discovery (PMTUD) that relies on TCP or some other Packetization Discovery (PMTUD) that relies on TCP or some other Packetization
Layer to probe an Internet path with progressively larger packets. Layer to probe an Internet path with progressively larger packets.
This method is described as an extension to RFC 1191 and RFC 1981, This method is described as an extension to RFC 1191 (see
which specify ICMP-based Path MTU Discovery for IP versions 4 and Section 3.6) and RFC 1981 (see Section 3.6), which specify ICMP-
6, respectively." [RFC4821] based Path MTU Discovery for IP versions 4 and 6, respectively."
[RFC4821]
3.7. Header Compression 3.7. Header Compression
Especially in streaming applications, the overhead of TCP/IP headers Especially in streaming applications, the overhead of TCP/IP headers
could correspond to more then 50% of the total amount of data sent. could correspond to more then 50% of the total amount of data sent.
Such large overheads may be tolerable in wired LANs where capacity is Such large overheads may be tolerable in wired LANs where capacity is
often not an issue, but are excessive for WANs and wireless systems often not an issue, but are excessive for WANs and wireless systems
where bandwidth is scarce. Header compression schemes for TCP/IP where bandwidth is scarce. Header compression schemes for TCP/IP
like "RObust Header Compression (ROHC) can significantly compress like "RObust Header Compression (ROHC) can significantly compress
this overhead. It performs well over links with significant error this overhead. It performs well over links with significant error
skipping to change at page 15, line 20 skipping to change at page 15, line 20
profile, called ROHC-TCP, provides efficient and robust profile, called ROHC-TCP, provides efficient and robust
compression of TCP headers, including frequently used TCP options compression of TCP headers, including frequently used TCP options
such as selective acknowledgments (SACKs) and Timestamps." such as selective acknowledgments (SACKs) and Timestamps."
[RFC6846] RFC 6846 is the successor of RFC 4996. It fixes a [RFC6846] RFC 6846 is the successor of RFC 4996. It fixes a
technical issue with the SACK compression and clarifies other technical issue with the SACK compression and clarifies other
compression methods used. compression methods used.
3.8. Defending Spoofing and Flooding Attacks 3.8. Defending Spoofing and Flooding Attacks
By default, TCP lacks any cryptographic structures to differentiate By default, TCP lacks any cryptographic structures to differentiate
legitimate segments and those spoofed from malicious hosts. Spoofing legitimate segments from those spoofed from malicious hosts.
valid segments requires correctly guessing a number of fields. The Spoofing valid segments requires correctly guessing a number of
documents in this sub-section describe ways to make that guessing fields. The documents in this sub-section describe ways to make that
harder, or to prevent it from being able to affect a connection guessing harder, or to prevent it from being able to affect a
negatively. connection negatively.
RFC 4953 I: "Defending TCP Against Spoofing Attacks" (July 2007) RFC 4953 I: "Defending TCP Against Spoofing Attacks" (July 2007)
This document [RFC4953] discusses the recently increased This document [RFC4953] discusses the recently increased
vulnerability of long-lived TCP connections, such as BGP vulnerability of long-lived TCP connections, such as BGP
connections, to reset (RST) spoofing attacks. The document connections, to reset (send RST) spoofing attacks. The document
analyzes the vulnerability, discussing proposed solutions at the analyzes the vulnerability, discussing proposed solutions at the
transport level and their inherent challenges, as well as existing transport level and their inherent challenges, as well as existing
network level solutions and the feasibility of their deployment. network level solutions and the feasibility of their deployment.
RFC 5461 I: "TCP's Reaction to Soft Errors" (February 2009) RFC 5461 I: "TCP's Reaction to Soft Errors" (February 2009)
This document [RFC5461] describes a non-standard but widely This document [RFC5461] describes a non-standard but widely
implemented modification to TCP's handling of ICMP soft error implemented modification to TCP's handling of ICMP soft error
messages that rejects pending connection-requests when such error messages that rejects pending connection-requests when such error
messages are received. This behavior reduces the likelihood of messages are received. This behavior reduces the likelihood of
skipping to change at page 16, line 14 skipping to change at page 16, line 14
RFC 5925 S: "The TCP Authentication Option" (May 2010) RFC 5925 S: "The TCP Authentication Option" (May 2010)
This document [RFC5925] describes the TCP Authentication Option This document [RFC5925] describes the TCP Authentication Option
(TCP-AO), which is used to authenticate TCP segments. TCP-AO (TCP-AO), which is used to authenticate TCP segments. TCP-AO
obsoletes the TCP MD5 Signature option of RFC 2385. It supports obsoletes the TCP MD5 Signature option of RFC 2385. It supports
the use of stronger hash functions, protects against replays for the use of stronger hash functions, protects against replays for
long-lived TCP connections (as used, e.g., in BGP and LDP), long-lived TCP connections (as used, e.g., in BGP and LDP),
coordinates key exchanges between endpoints, and provides a more coordinates key exchanges between endpoints, and provides a more
explicit recommendation for external key management. explicit recommendation for external key management.
Cryptographic algorithms for TCP-AO are defined in [RFC5926]. Cryptographic algorithms for TCP-AO are defined in [RFC5926] (see
Section 3.8).
RFC 5926 S: "Cryptographic Algorithms for the TCP Authentication RFC 5926 S: "Cryptographic Algorithms for the TCP Authentication
Option (TCP-AO)" (May 2010) Option (TCP-AO)" (May 2010)
This document [RFC5926] specifies the algorithms and attributes This document [RFC5926] specifies the algorithms and attributes
that can be used in TCP Authentication Option's (TCP-AO) current that can be used in TCP Authentication Option's (TCP-AO) [RFC5925]
manual keying mechanism and provides the interface for future (see Section 3.8) current manual keying mechanism and provides the
message authentication codes (MACs). interface for future message authentication codes (MACs).
RFC 5927 I: "ICMP attacks against TCP" (July 2010) RFC 5927 I: "ICMP attacks against TCP" (July 2010)
Abstract: "This document discusses the use of the Internet Control Abstract: "This document discusses the use of the Internet Control
Message Protocol (ICMP) to perform a variety of attacks against Message Protocol (ICMP) to perform a variety of attacks against
the Transmission Control Protocol (TCP). Additionally, this the Transmission Control Protocol (TCP). Additionally, this
document describes a number of widely implemented modifications to document describes a number of widely implemented modifications to
TCP's handling of ICMP error messages that help to mitigate these TCP's handling of ICMP error messages that help to mitigate these
issues." [RFC5927] issues." [RFC5927]
skipping to change at page 16, line 52 skipping to change at page 17, line 4
RFC 6528 S: "Defending Against Sequence Number Attacks" (February RFC 6528 S: "Defending Against Sequence Number Attacks" (February
2012) 2012)
Abstract: "This document [RFC6528] specifies an algorithm for the Abstract: "This document [RFC6528] specifies an algorithm for the
generation of TCP Initial Sequence Numbers (ISNs), such that the generation of TCP Initial Sequence Numbers (ISNs), such that the
chances of an off-path attacker guessing the sequence numbers in chances of an off-path attacker guessing the sequence numbers in
use by a target connection are reduced. This document revises use by a target connection are reduced. This document revises
(and formally obsoletes) RFC 1948, and takes the ISN generation (and formally obsoletes) RFC 1948, and takes the ISN generation
algorithm originally proposed in that document to Standards Track, algorithm originally proposed in that document to Standards Track,
formally updating RFC 793. formally updating RFC 793 (see Section 2).
4. Experimental Extensions 4. Experimental Extensions
The RFCs in this section are still experimental, but they may become The RFCs in this section are still experimental, but they may become
proposed standards in the future. At least part of the reason that proposed standards in the future. At least part of the reason that
they are still experimental is to gain more wide-scale experience they are still experimental is to gain more wide-scale experience
with them before a standards track decision is made. with them before a standards track decision is made.
At this point is worth mentioning that if the experimental RFC is a At this point is worth mentioning that if the experimental RFC is a
proposal for a new protocol capability or service, i.e., it requires proposal for a new protocol capability or service, i.e., it requires
skipping to change at page 17, line 47 skipping to change at page 17, line 48
same endpoints might share information, such as their congestion same endpoints might share information, such as their congestion
control state. To some degree, this is done in practice by a few control state. To some degree, this is done in practice by a few
operating systems; for example, Linux currently has a destination operating systems; for example, Linux currently has a destination
cache. Although this RFC is technically informational, the cache. Although this RFC is technically informational, the
concepts it describes are in experimental use, so we include it in concepts it describes are in experimental use, so we include it in
this section. this section.
RFC 3124 S: "The Congestion Manager" (June 2001) RFC 3124 S: "The Congestion Manager" (June 2001)
This document [RFC3124], the Congestion Manager, is a related This document [RFC3124], the Congestion Manager, is a related
proposal to RFC 2140. The idea behind the Congestion Manager, proposal to RFC 2140 (see Section 4.1). The idea behind the
moving congestion control outside of individual TCP connections, Congestion Manager, moving congestion control outside of
represents a modification to the core of TCP, which supports individual TCP connections, represents a modification to the core
sharing information among TCP connections. Although a Proposed of TCP, which supports sharing information among TCP connections.
Standard, some pieces of the Congestion Manager support Although a Proposed Standard, some pieces of the Congestion
architecture have not been specified yet, and it has not achieved Manager support architecture have not been specified yet, and it
use or implementation beyond experimental stacks, so it is not has not achieved use or implementation beyond experimental stacks,
listed among the standard TCP enhancements in this roadmap. so it is not listed among the standard TCP enhancements in this
roadmap.
4.2. Congestion Control Extensions 4.2. Congestion Control Extensions
TCP congestion control has been an extremely active research area for TCP congestion control has been an extremely active research area for
many years (see [RFC5783], as it determines the performance of many many years (see RFC 5783, Section 7.6), as it determines the
applications that use TCP. A number of experimental RFCs address performance of many applications that use TCP. A number of
issues with flow start-up, overshoot, and steady-state behavior in experimental RFCs address issues with flow start-up, overshoot, and
the basic RFC 5681 algorithms. In this sub-sections, enhancements to steady-state behavior in the basic RFC 5681 (see Section 2)
TCP's congestion control are listed. The next sub-section focus on algorithms. In this sub-sections, enhancements to TCP's congestion
TCP's loss recovery. control are listed. The next sub-section focus on TCP's loss
recovery.
RFC 2861 E: "TCP Congestion Window Validation" (June 2000) RFC 2861 E: "TCP Congestion Window Validation" (June 2000)
This document [RFC2861] suggests reducing the congestion window This document [RFC2861] suggests reducing the congestion window
over time when no packets are flowing. This behavior is more over time when no packets are flowing. This behavior is more
aggressive than that specified in RFC 5681, which says that a TCP aggressive than that specified in RFC 5681 (see Section 2), which
sender SHOULD set its congestion window to the initial window says that a TCP sender SHOULD set its congestion window to the
after an idle period of an RTO or greater. initial window after an idle period of an RTO or greater.
RFC 3540 E: "Robust Explicit Congestion Notification (ECN) signaling RFC 3540 E: "Robust Explicit Congestion Notification (ECN) signaling
with Nonces" (June 2003) with Nonces" (June 2003)
This document [RFC3540] describes an optional addition to ECN that This document [RFC3540] describes an optional addition to ECN that
protects against accidental or malicious concealment of marked protects against accidental or malicious concealment of marked
packets from the TCP sender. packets from the TCP sender.
RFC 3649 E: "HighSpeed TCP for Large Congestion Windows" (December RFC 3649 E: "HighSpeed TCP for Large Congestion Windows" (December
2003) 2003)
skipping to change at page 19, line 12 skipping to change at page 19, line 18
mechanism for TCP. This mechanism allows connections to use mechanism for TCP. This mechanism allows connections to use
higher sending rates at the beginning of the data transfer or higher sending rates at the beginning of the data transfer or
after an idle period, provided that there is significant unused after an idle period, provided that there is significant unused
bandwidth along the path, and the sender and all of the routers bandwidth along the path, and the sender and all of the routers
along the path approve this higher rate. along the path approve this higher rate.
RFC 5562 E: "Adding Explicit Congestion Notification (ECN) Capability RFC 5562 E: "Adding Explicit Congestion Notification (ECN) Capability
to TCP's SYN/ACK Packets" (June 2009) to TCP's SYN/ACK Packets" (June 2009)
This document [RFC5562] describes an experimental modification to This document [RFC5562] describes an experimental modification to
ECN [RFC3168] for the use of ECN in TCP SYN/ACK packets. This ECN [RFC3168] (see Section 3.2) for the use of ECN in TCP SYN/ACK
would allow to ECN-mark rather than drop the TCP SYN/ACK packet at packets. This would allow to ECN-mark rather than drop the TCP
an ECN-capable router, and to avoid the severe penalty of a SYN/ACK packet at an ECN-capable router, and to avoid the severe
retransmission timeout for a connection when the SYN/ACK packet is penalty of a retransmission timeout for a connection when the SYN/
dropped. ACK packet is dropped.
RFC 5690 I: "Adding Acknowledgement Congestion Control to TCP" RFC 5690 I: "Adding Acknowledgement Congestion Control to TCP"
(February 2010) (February 2010)
This document [RFC5690] describes a congestion control mechanism This document [RFC5690] describes a congestion control mechanism
for acknowledgment (ACKs) traffic in TCP. The mechanism is based for acknowledgment (ACKs) traffic in TCP. The mechanism is based
on the acknowledgment congestion control of the Datagram on the acknowledgment congestion control of the Datagram
Congestion Control Protocol's (DCCP's) [RFC4340] Congestion Congestion Control Protocol's (DCCP's) [RFC4340] Congestion
Control Identifier (CCID) 2 [RFC4341]. Control Identifier (CCID) 2 [RFC4341].
RFC 6928 E: "Increasing TCP's Initial Window" (April 2013) RFC 6928 E: "Increasing TCP's Initial Window" (April 2013)
This document [RFC6928] proposes to increase the TCP initial This document [RFC6928] proposes to increase the TCP initial
window from between 2 and 4 segments, as specified in RFC 3390, to window from between 2 and 4 segments, as specified in RFC 3390
10 segments with a fallback to the existing recommendation when (see Section 3.2), to 10 segments with a fallback to the existing
performance issues are detected. recommendation when performance issues are detected.
4.3. Loss Recovery Extensions 4.3. Loss Recovery Extensions
RFC 5827 E: "Early Retransmit for TCP and SCTP" (April 2010) RFC 5827 E: "Early Retransmit for TCP and SCTP" (April 2010)
This document [RFC5827] proposes the "Early Retransmit" mechanism This document [RFC5827] proposes the "Early Retransmit" mechanism
for TCP (and SCTP) that can be used to recover lost segments when for TCP (and SCTP) that can be used to recover lost segments when
a connection's congestion window is small. In certain special a connection's congestion window is small. In certain special
circumstances, Early Retransmit reduces the number of duplicate circumstances, Early Retransmit reduces the number of duplicate
acknowledgments required to trigger fast retransmit to recover acknowledgments required to trigger fast retransmit to recover
skipping to change at page 22, line 10 skipping to change at page 22, line 11
Abstract: "This memo provides guidance for the IANA to use in Abstract: "This memo provides guidance for the IANA to use in
assigning parameters for fields in the IPv4, IPv6, ICMP, UDP and assigning parameters for fields in the IPv4, IPv6, ICMP, UDP and
TCP protocol headers."[RFC2780] TCP protocol headers."[RFC2780]
RFC 4727 S: "Experimental Values" (November 2006) RFC 4727 S: "Experimental Values" (November 2006)
This document [RFC4727] reserves both TCP options 253 and 254 for This document [RFC4727] reserves both TCP options 253 and 254 for
experimentation purposes. When such experiments are deployed in experimentation purposes. When such experiments are deployed in
the Internet, they should follow the additional requirements in the Internet, they should follow the additional requirements in
RFC 6994. RFC 6994 (see Section 5).
RFC 6335 B: "Internet Assigned Numbers Authority (IANA) Procedures RFC 6335 B: "Internet Assigned Numbers Authority (IANA) Procedures
for the Management of the Service Name and Transport Protocol Port for the Management of the Service Name and Transport Protocol Port
Number Registry (August 2011) Number Registry (August 2011)
From abstract: "This document defines the procedures that the From abstract: "This document defines the procedures that the
Internet Assigned Numbers Authority (IANA) uses when handling Internet Assigned Numbers Authority (IANA) uses when handling
assignment and other requests related to the Service Name and assignment and other requests related to the Service Name and
Transport Protocol Port Number registry." [RFC6335] Transport Protocol Port Number registry." [RFC6335]
skipping to change at page 22, line 33 skipping to change at page 22, line 34
This document [RFC6994] describes how the experimental TCP option This document [RFC6994] describes how the experimental TCP option
code points can concurrently support multiple TCP extensions, even code points can concurrently support multiple TCP extensions, even
within the same connection. It creates an IANA registry for within the same connection. It creates an IANA registry for
extensions to the experimental code points. extensions to the experimental code points.
6. Historic and Undeployed Extensions 6. Historic and Undeployed Extensions
The RFCs listed here define extensions that have thus far failed to The RFCs listed here define extensions that have thus far failed to
arouse substantial interest from implementers and have never seen arouse substantial interest from implementers and have never seen
widespread deployment, or were found to be defective for general use. widespread deployment, or were found to be defective for general use.
Most of them are reclassified by RFC 6247 [RFC6247] to Historic Most of them are reclassified by [RFC6247] to Historic status.
status.
RFC 721 U: "Out-of-Band Control Signals in a Host-to-Host Protocol" RFC 721 U: "Out-of-Band Control Signals in a Host-to-Host Protocol"
(September 1976): lack of interest (September 1976): lack of interest
RFC 721 [RFC0721] addresses the problem of implementing a reliable RFC 721 [RFC0721] addresses the problem of implementing a reliable
out-of-band signal (interrupts) for use in a host-to-host out-of-band signal (interrupts) for use in a host-to-host
protocol. The proposal was not included in the final TCP protocol. The proposal was not included in the final TCP
specification. specification.
RFC 1078 U: "TCP Port Service Multiplexer (TCPMUX)" (November 1988): RFC 1078 U: "TCP Port Service Multiplexer (TCPMUX)" (November 1988):
skipping to change at page 23, line 12 skipping to change at page 23, line 12
services on a single well-known TCP port using a service name services on a single well-known TCP port using a service name
instead of a well-known number. instead of a well-known number.
RFC 1106 H: "TCP Big Window and NAK Options" (June 1989): found RFC 1106 H: "TCP Big Window and NAK Options" (June 1989): found
defective defective
This RFC [RFC1106] defined an alternative to the Window Scale This RFC [RFC1106] defined an alternative to the Window Scale
option for using large windows and described the "negative option for using large windows and described the "negative
acknowledgment" or NAK option. There is a comparison of NAK and acknowledgment" or NAK option. There is a comparison of NAK and
SACK methods, and early discussion of TCP over satellite issues. SACK methods, and early discussion of TCP over satellite issues.
RFC 1110 explains some problems with the approaches described in RFC 1110 (see Section 6) explains some problems with the
RFC 1106. The options described in this document have not been approaches described in RFC 1106. The options described in this
adopted by the larger community, although NAKs are used in the document have not been adopted by the larger community, although
SCPS-TP adaptation of TCP for satellite and spacecraft use, NAKs are used in the SCPS-TP adaptation of TCP for satellite and
developed by the Consultative Committee for Space Data Systems spacecraft use, developed by the Consultative Committee for Space
(CCSDS). Data Systems (CCSDS).
RFC 1110 H: "A Problem with the TCP Big Window Option" (August 1989): RFC 1110 H: "A Problem with the TCP Big Window Option" (August 1989):
deprecates RFC 1106 deprecates RFC 1106
Abstract: "The TCP Big Window option discussed in RFC 1106 will Abstract: "The TCP Big Window option discussed in RFC 1106 (see
not work properly in an Internet environment which has both a high Section 6) will not work properly in an Internet environment which
bandwidth * delay product and the possibility of disordering and has both a high bandwidth * delay product and the possibility of
duplicating packets. In such networks, the window size must not disordering and duplicating packets. In such networks, the window
be increased without a similar increase in the sequence number size must not be increased without a similar increase in the
space. Therefore, a different approach to big windows should be sequence number space. Therefore, a different approach to big
taken in the Internet." [RFC1110] windows should be taken in the Internet." [RFC1110]
RFC 1146 H: "TCP Alternate Checksum Options" (March 1990): lack of RFC 1146 H: "TCP Alternate Checksum Options" (March 1990): lack of
interest interest
This document [RFC1146] defined more robust TCP checksums than the This document [RFC1146] defined more robust TCP checksums than the
16-bit ones-complement in use today. A typographical error in RFC 16-bit ones-complement in use today. A typographical error in RFC
1145 is fixed in RFC 1146; otherwise, the documents are the same. 1145 is fixed in RFC 1146; otherwise, the documents are the same.
RFC 1263 I: "TCP Extensions Considered Harmful" (October 1991): lack RFC 1263 I: "TCP Extensions Considered Harmful" (October 1991): lack
of interest of interest
skipping to change at page 24, line 8 skipping to change at page 24, line 8
upgrades to each other and could be header-incompatible. upgrades to each other and could be header-incompatible.
Interoperability would be provided by having a virtualization Interoperability would be provided by having a virtualization
layer select the right TCP version for a particular connection. layer select the right TCP version for a particular connection.
This idea did not catch on with the community, while the type of This idea did not catch on with the community, while the type of
extensions RFC 1263 specifically targeted as harmful did become extensions RFC 1263 specifically targeted as harmful did become
popular. popular.
RFC 1379 H: "Extending TCP for Transactions -- Concepts" (November RFC 1379 H: "Extending TCP for Transactions -- Concepts" (November
1992): found defective 1992): found defective
See RFC 1644. See RFC 1644, Section 6.
RFC 1644 H: "T/TCP -- TCP Extensions for Transactions Functional RFC 1644 H: "T/TCP -- TCP Extensions for Transactions Functional
Specification" (July 1994): found defective Specification" (July 1994): found defective
The inventors of TCP believed that cached connection state could The inventors of TCP believed that cached connection state could
have been used to eliminate TCP's 3-way handshake, to support two- have been used to eliminate TCP's 3-way handshake, to support two-
packet request/response exchanges. RFCs 1379 [RFC1379] and 1644 packet request/response exchanges. RFC 1379 [RFC1379] (see
[RFC1644] show that this is far from simple. Furthermore, T/TCP Section 6) and RFC 1644 [RFC1644] show that this is far from
floundered on the ease of denial-of-service attacks that can simple. Furthermore, T/TCP floundered on the ease of denial-of-
result. One idea pioneered by T/TCP lives on in RFC 2140, in the service attacks that can result. One idea pioneered by T/TCP
sharing of state across connections. lives on in RFC 2140 (see Section 4.1), in the sharing of state
across connections.
RFC 1693 H: "An Extension to TCP: Partial Order Service" (November RFC 1693 H: "An Extension to TCP: Partial Order Service" (November
1994): lack of interest 1994): lack of interest
This document [RFC1693] defines a TCP extension for applications This document [RFC1693] defines a TCP extension for applications
that do not care about the order in which application-layer that do not care about the order in which application-layer
objects are received. Examples are multimedia and database objects are received. Examples are multimedia and database
applications. In practice, these applications either accept the applications. In practice, these applications either accept the
possible performance loss because of TCP's strict ordering or they possible performance loss because of TCP's strict ordering or they
use more specialized transport protocols. use specialized transport protocols other than TCP, such as PR-
SCTP [RFC3758].
RFC 1705 I: "Six Virtual Inches to the Left: The Problem with IPng" RFC 1705 I: "Six Virtual Inches to the Left: The Problem with IPng"
(October 1994): lack of interest (October 1994): lack of interest
To overcome the exhaustion of the IP class B address space, To overcome the exhaustion of the IP class B address space,
suggest this document [RFC1705] that a new version of TCP (TCPng) suggest this document [RFC1705] that a new version of TCP (TCPng)
needs to be developed and deployed. It proposes that a globally needs to be developed and deployed. It proposes that a globally
unique address be assigned to Transport layer to uniquely identify unique address be assigned to Transport layer to uniquely identify
an Internet host without specifying any routing information. an Internet host without specifying any routing information.
Later work on splitting locator and identifier values is
summarized well in [RFC6115], but no resulting changes to TCP have
occurred.
RFC 6013 E: "TCP Cookie Transactions (TCPCT)" (January 2011): lack of RFC 6013 E: "TCP Cookie Transactions (TCPCT)" (January 2011): lack of
interest interest
This document [RFC6013] describes a method to exchange a cookie This document [RFC6013] describes a method to exchange a cookie
(nonce) during the connection establishment to negotiate (nonce) during the connection establishment to negotiate
elimination of receiver state. These cookies are later used to elimination of receiver state. These cookies are later used to
inhibit premature closing of connections, and reduce retention of inhibit premature closing of connections, and reduce retention of
state after the connection has terminated. state after the connection has terminated.
skipping to change at page 25, line 47 skipping to change at page 26, line 9
However, some of them contain a greater depth of problem statement However, some of them contain a greater depth of problem statement
explanation or other context. Particularly, RFCs 813 - 817 (known as explanation or other context. Particularly, RFCs 813 - 817 (known as
the "Dave Clark Five") describe some early problems and solutions the "Dave Clark Five") describe some early problems and solutions
(RFC 815 only describes the reassembly of IP fragments and is not (RFC 815 only describes the reassembly of IP fragments and is not
included in this TCP roadmap). included in this TCP roadmap).
RFC 675 U: "Specification of Internet Transmission Control Program" RFC 675 U: "Specification of Internet Transmission Control Program"
(December 1974) (December 1974)
This document [RFC0675] is a very early precursor of the This document [RFC0675] is a very early precursor of the
fundamental RFC 793 which already contained the three-way fundamental RFC 793 (see Section 2), which already contained the
handshake in its final form and the concept of sliding windows for three-way handshake in its final form and the concept of sliding
reliable data transmission. Apart from that the segment layout is windows for reliable data transmission. Apart from that the
totally different and the specified API differs from the latter segment layout is totally different and the specified API differs
RFC 793. from the latter RFC 793 (see Section 2).
RFC 761 H: "DoD standard Transmission Control Protocol" (Januar RFC 761 H: "DoD standard Transmission Control Protocol" (Januar
1980) 1980)
This document [RFC0761] is the immediate precursor of RFC 793. This document [RFC0761] is the immediate precursor of RFC 793 (see
The header format, the connection establishment including the Section 2). The header format, the connection establishment
different connection states, and the overall API correspond mostly including the different connection states, and the overall API
the final Standard RFC 793. correspond mostly to the final Standard RFC 793 (see Section 2).
RFC 813 U: "Window and Acknowledgement Strategy in TCP" (July 1982) RFC 813 U: "Window and Acknowledgement Strategy in TCP" (July 1982)
This document [RFC0813] contains an early discussion of Silly This document [RFC0813] contains an early discussion of Silly
Window Syndrome and its avoidance and motivates and describes the Window Syndrome and its avoidance and motivates and describes the
use of delayed acknowledgments. use of delayed acknowledgments.
RFC 814 U: "Name, Addresses, Ports, and Routes" (July 1982) RFC 814 U: "Name, Addresses, Ports, and Routes" (July 1982)
Suggestions and guidance for the design of tables and algorithms Suggestions and guidance for the design of tables and algorithms
skipping to change at page 26, line 40 skipping to change at page 27, line 5
RFC 817 U: "Modularity and Efficiency in Protocol Implementation" RFC 817 U: "Modularity and Efficiency in Protocol Implementation"
(July 1982) (July 1982)
This document [RFC0817] contains implementation suggestions that This document [RFC0817] contains implementation suggestions that
are general and not TCP specific. However, they have been used to are general and not TCP specific. However, they have been used to
develop TCP implementations and describe some performance develop TCP implementations and describe some performance
implications of the interactions between various layers in the implications of the interactions between various layers in the
Internet stack. Internet stack.
RFC 872 U: "TCP-ON-A-LAN" (September 1982) RFC 872 U: "TCP-on-a-LAN" (September 1982)
Conclusion: "The sometimes-expressed fear that using TCP on a Conclusion: "The sometimes-expressed fear that using TCP on a
local net is a bad idea is unfounded." [RFC0872] local net is a bad idea is unfounded." [RFC0872]
RFC 896 U: "Congestion Control in IP/TCP Internetworks" (January RFC 896 U: "Congestion Control in IP/TCP Internetworks" (January
1984) 1984)
This document [RFC0896] contains some early experiences with This document [RFC0896] contains some early experiences with
congestion collapse and some initial thoughts on how to avoid it congestion collapse and some initial thoughts on how to avoid it
using congestion control in TCP. using congestion control in TCP. Furthermore, it defined an
algorithm for efficient transmission of small packets that is
today known as the Nagle Algorithm.
RFC 964 U: "Some Problems with the Specification of the Military RFC 964 U: "Some Problems with the Specification of the Military
Standard Transmission Control Protocol" (November 1985) Standard Transmission Control Protocol" (November 1985)
This document [RFC0964] points out several specification bugs in This document [RFC0964] points out several specification bugs in
the US Military's MIL-STD-1778 document, which was intended as a the US Military's MIL-STD-1778 document, which was intended as a
successor to RFC 793. This serves to remind us of the difficulty successor to RFC 793 (see Section 2). This serves to remind us of
in specification writing (even when we work from existing the difficulty in specification writing (even when we work from
documents!). existing documents!).
7.2. Architectural Guidelines 7.2. Architectural Guidelines
Some documents in this section contain architectural guidance and Some documents in this section contain architectural guidance and
concerns, while others specify TCP- and congestion-control-related concerns, while others specify TCP- and congestion-control-related
mechanisms that are broadly applicable and have impacts on TCP's mechanisms that are broadly applicable and have impacts on TCP's
congestion control techniques. Some of these documents are direct congestion control techniques. Some of these documents are direct
products of the Internet Architecture Board (IAB), giving their products of the Internet Architecture Board (IAB), giving their
guidance on specific aspects of congestion control in the Internet. guidance on specific aspects of congestion control in the Internet.
RFC 1958 I: "Architectural Principles of the Internet" (June 1996) RFC 1958 I: "Architectural Principles of the Internet" (June 1996)
This document [RFC1958] describes the underlying principles of the This document [RFC1958] describes the underlying principles of the
Internet architecture. It provides guidelines for network systems Internet architecture. It provides guidelines for network systems
design that have proven useful in the evolution of the Internet. design that have proven useful in the evolution of the Internet.
RFC 2914 B: "Congestion Control Principles" (September 2000) RFC 2914 B: "Congestion Control Principles" (September 2000)
This document [RFC2914] motivates the use of end-to-end congestion This document [RFC2914] motivates the use of end-to-end congestion
control for preventing congestion collapse and providing fairness control for preventing congestion collapse and providing fairness
to TCP. to TCP. Later work on TCP has included several more aggressive
mechanisms than Reno TCP includes, and RFC 5033 (see Section 7.4)
provides additional guidance on use of such algorithms. The
fundamental architectural discussion in RFC 2914 remains valid,
regarding the standards process role in defining protocol aspects
that are critical to performance and avoiding congestion collapse
scenarios.
RFC 3439 I: "Some Internet Architectural Guidelines and Philosophy" RFC 3439 I: "Some Internet Architectural Guidelines and Philosophy"
(December 2002) (December 2002)
This document [RFC3439] extends RFC 1958 by outlining some This document [RFC3439] updates RFC 1958 (see Section 7.2) by
philosophical guidelines for architects and designers of Internet outlining some philosophical guidelines for architects and
backbone networks. The document describes the Simplicity designers of Internet backbone networks. The document describes
Principle, which states that complexity is the primary mechanism the Simplicity Principle, which states that complexity is the
that impedes efficient scaling. primary impediment to efficient scaling.
RFC 4774 B: "Specifying Alternate Semantics for the Explicit
Congestion Notification (ECN) Field" (November 2006)
This document [RFC4774] discusses some of the issues in defining
alternate semantics for the ECN field, and specifies requirements
for a safe co-existence with routers that do not understand the
defined alternate semantics.
RFC 6182 I: "Architectural Guidelines for Multipath TCP Development" RFC 6182 I: "Architectural Guidelines for Multipath TCP Development"
(March 2011) (March 2011)
Abstract: "This document outlines architectural guidelines for the Abstract: "This document outlines architectural guidelines for the
development of a Multipath Transport Protocol, with references to development of a Multipath Transport Protocol, with references to
how these architectural components come together in the how these architectural components come together in the
development of a Multipath TCP (MPTCP). This document lists development of a Multipath TCP (MPTCP) (see Section 4.5). This
certain high-level design decisions that provide foundations for document lists certain high-level design decisions that provide
the design of the MPTCP protocol, based upon these architectural foundations for the design of the MPTCP protocol, based upon these
requirements" [RFC6182] architectural requirements" [RFC6182]
7.3. Difficult Network Environments 7.3. Difficult Network Environments
As the internetworking field has explored wireless, satellite, As the internetworking field has explored wireless, satellite,
cellular telephone, and other kinds of link-layer technologies, a cellular telephone, and other kinds of link-layer technologies, a
large body of work has built up on enhancing TCP performance for such large body of work has built up on enhancing TCP performance for such
links. The RFCs listed in this section describe some of these more links. The RFCs listed in this section describe some of these more
challenging network environments and how TCP interacts with them. challenging network environments and how TCP interacts with them.
RFC 2488 B: "Enhancing TCP Over Satellite Channels using Standard RFC 2488 B: "Enhancing TCP Over Satellite Channels using Standard
skipping to change at page 28, line 28 skipping to change at page 29, line 8
several IETF standardized mechanisms that enable TCP to more several IETF standardized mechanisms that enable TCP to more
effectively utilize the available capacity of the network path. effectively utilize the available capacity of the network path.
This document outlines some of these TCP mitigations. At this This document outlines some of these TCP mitigations. At this
time, all mitigations discussed in this document are IETF time, all mitigations discussed in this document are IETF
standards track mechanisms (or are compliant with IETF standards track mechanisms (or are compliant with IETF
standards)." [RFC2488] standards)." [RFC2488]
RFC 2757 I: "Long Thin Networks" (January 2000) RFC 2757 I: "Long Thin Networks" (January 2000)
Several methods of improving TCP performance over long thin Several methods of improving TCP performance over long thin
networks, such as geosynchronous satellite links, are discussed in networks (i.e., networks with low bandwidth and high delay), such
this document [RFC2757]. A particular set of TCP options is as geosynchronous satellite links, are discussed in this document
developed that should work well in such environments and be safe [RFC2757]. A particular set of TCP options is developed that
to use in the global Internet. The implications of such should work well in such environments and be safe to use in the
environments have been further discussed in RFC 3150 and RFC 3155, global Internet. The implications of such environments have been
and these documents should be preferred where there is overlap further discussed in RFC 3150 (see Section 7.3) and RFC 3155 (see
between them and RFC 2757. Section 7.3), and these documents should be preferred where there
is overlap between them and RFC 2757 (see Section 7.3).
RFC 2760 I: "Ongoing TCP Research Related to Satellites" (February RFC 2760 I: "Ongoing TCP Research Related to Satellites" (February
2000) 2000)
This document [RFC2760] discusses the advantages and disadvantages This document [RFC2760] discusses the advantages and disadvantages
of several different experimental means of improving TCP of several different experimental means of improving TCP
performance over long-delay or error-prone paths. These include performance over long-delay or error-prone paths. These include
T/TCP, larger initial windows, byte counting, delayed T/TCP, larger initial windows, byte counting, delayed
acknowledgments, slow start thresholds, NewReno and SACK-based acknowledgments, slow start thresholds, NewReno and SACK-based
loss recovery, FACK [MM96], ECN, various corruption-detection loss recovery, FACK [MM96], ECN, various corruption-detection
mechanisms, congestion avoidance changes for fairness, use of mechanisms, congestion avoidance changes for fairness, use of
multiple parallel flows, pacing, header compression, state multiple parallel flows, pacing, header compression, state
sharing, and ACK congestion control, filtering, and sharing, and ACK congestion control, filtering, and
reconstruction. Although RFC 2488 looks at standard extensions, reconstruction. Although RFC 2488 (see Section 7.3) looks at
this document focuses on more experimental means of performance standard extensions, this document focuses on more experimental
enhancement. means of performance enhancement.
RFC 3135 I: "Performance Enhancing Proxies Intended to Mitigate Link- RFC 3135 I: "Performance Enhancing Proxies Intended to Mitigate Link-
Related Degradations" (June 2001) Related Degradations" (June 2001)
From abstract: "This document is a survey of Performance Enhancing From abstract: "This document is a survey of Performance Enhancing
Proxies (PEPs) often employed to improve degraded TCP performance Proxies (PEPs) often employed to improve degraded TCP performance
caused by characteristics of specific link environments, for caused by characteristics of specific link environments, for
example, in satellite, wireless WAN, and wireless LAN example, in satellite, wireless WAN, and wireless LAN
environments. Different types of Performance Enhancing Proxies environments. Different types of Performance Enhancing Proxies
are described as well as the mechanisms used to improve are described as well as the mechanisms used to improve
skipping to change at page 30, line 28 skipping to change at page 31, line 10
From abstract: "This document describes a profile for optimizing From abstract: "This document describes a profile for optimizing
TCP to adapt so that it handles paths including second (2.5G) and TCP to adapt so that it handles paths including second (2.5G) and
third (3G) generation wireless networks." [RFC3481] third (3G) generation wireless networks." [RFC3481]
RFC 3819 B: "Advice for Internet Subnetwork Designers" (July 2004) RFC 3819 B: "Advice for Internet Subnetwork Designers" (July 2004)
This document [RFC3819] describes how TCP performance can be This document [RFC3819] describes how TCP performance can be
negatively affected by some particular lower-layer behaviors and negatively affected by some particular lower-layer behaviors and
provides guidance in designing lower-layer networks and protocols provides guidance in designing lower-layer networks and protocols
to be amicable to TCP. to be amicable to TCP. RFC 3366 (see Section 7.3) specifically
focuses on ARQ mechanisms, while RFC 3819 more widely covers
additional aspects of the underlying layers
7.4. Guidance for Developing, Analyzing, and Evaluating TCP 7.4. Guidance for Developing, Analyzing, and Evaluating TCP
Documents in this section give general guidance for developing, Documents in this section give general guidance for developing,
analyzing, and evaluating TCP. Some of the documents discuss for analyzing, and evaluating TCP. Some of the documents discuss for
example the properties of congestion control protocols that are example the properties of congestion control protocols that are
"safe" for Internet deployment, as well as how to measure the "safe" for Internet deployment, as well as how to measure the
properties of congestion control mechanisms and transport protocols. properties of congestion control mechanisms and transport protocols.
RFC 4774 B: "Specifying Alternate Semantics for the Explicit
Congestion Notification (ECN) Field" (November 2006)
This document [RFC4774] discusses some of the issues in defining
alternate semantics for the ECN field, and specifies requirements
for a safe co- existence in an Internet that may include routers
that do not understand the defined alternate semantics.
RFC 5033 B: "Specifying New Congestion Control Algorithms" (August RFC 5033 B: "Specifying New Congestion Control Algorithms" (August
2007) 2007)
This document [RFC5033] considers the evaluation of suggested This document [RFC5033] considers the evaluation of suggested
congestion control algorithms that differ from the principles congestion control algorithms that differ from the principles
outlined in RFC 2914. It is useful for authors of such algorithms outlined in RFC 2914 (see Section 7.2). It is useful for authors
as well as for IETF members reviewing the associated documents. of such algorithms as well as for IETF members reviewing the
associated documents.
RFC 5166 I: "Metrics for the Evaluation of Congestion Control RFC 5166 I: "Metrics for the Evaluation of Congestion Control
Mechanisms" (March 2008) Mechanisms" (March 2008)
This document [RFC5166] discusses metrics that needs to be This document [RFC5166] discusses metrics that needs to be
considered when evaluating new or modified congestion control considered when evaluating new or modified congestion control
mechanisms for the Internet. Among others topics, the document mechanisms for the Internet. Among others topics, the document
discusses throughput, delay, loss rates, response times, fairness discusses throughput, delay, loss rates, response times, fairness
and robustness for challenging environments. and robustness for challenging environments.
skipping to change at page 31, line 28 skipping to change at page 32, line 4
This RFC [RFC6077] summarizes the main open problems in the domain This RFC [RFC6077] summarizes the main open problems in the domain
of Internet congestion control. As a good starting point for of Internet congestion control. As a good starting point for
newcomers, the document describes several new challenges that are newcomers, the document describes several new challenges that are
becoming important as the network grows, as well as some issues becoming important as the network grows, as well as some issues
that have been known for many years. that have been known for many years.
RFC 6181 I: "Threat Analysis for TCP Extensions for Multipath RFC 6181 I: "Threat Analysis for TCP Extensions for Multipath
Operation with Multiple Addresses" (March 2011) Operation with Multiple Addresses" (March 2011)
This document [RFC6181] describes a threat analysis for Multipath This document [RFC6181] describes a threat analysis for Multipath
TCP (MPTCP). The document discusses several types of attacks and TCP (MPTCP) (see Section 4.5). The document discusses several
provides recommendations for MPTCP designers how to create an types of attacks and provides recommendations for MPTCP designers
MPTCP specification that is as secure as the current (single-path) how to create an MPTCP specification that is as secure as the
TCP. current (single-path) TCP.
RFC 6349 I: "Framework for TCP Throughput Testing" (August 2011) RFC 6349 I: "Framework for TCP Throughput Testing" (August 2011)
From abstract: "This document describes a practical methodology From abstract: "This document describes a practical methodology
for measuring end-to-end TCP throughput in a managed IP network. for measuring end-to-end TCP throughput in a managed IP network.
The goal is to provide a better indication in regard to user The goal is to provide a better indication in regard to user
experience. In this framework, TCP and IP parameters are experience. In this framework, TCP and IP parameters are
specified to optimize TCP throughput." [RFC6349] specified to optimize TCP throughput." [RFC6349]
7.5. Implementation Advice 7.5. Implementation Advice
skipping to change at page 32, line 23 skipping to change at page 32, line 47
techniques for efficiently computing the Internet checksum (used techniques for efficiently computing the Internet checksum (used
by TCP). by TCP).
RFC 1624 I: "Computation of the Internet Checksum via Incremental RFC 1624 I: "Computation of the Internet Checksum via Incremental
Update" (May 1994) Update" (May 1994)
Incrementally updating the Internet checksum is useful to routers Incrementally updating the Internet checksum is useful to routers
in updating IP checksums. Some middleboxes that alter TCP headers in updating IP checksums. Some middleboxes that alter TCP headers
may also be able to update the TCP checksum incrementally. This may also be able to update the TCP checksum incrementally. This
document [RFC1624] expands upon the explanation of the incremental document [RFC1624] expands upon the explanation of the incremental
update procedure in RFC 1071. update procedure in RFC 1071 (see Section 7.5).
RFC 1936 I: "Implementing the Internet Checksum in Hardware" (April RFC 1936 I: "Implementing the Internet Checksum in Hardware" (April
1996) 1996)
This document [RFC1936] describes the motivation for implementing This document [RFC1936] describes the motivation for implementing
the Internet checksum in hardware, rather than in software, and the Internet checksum in hardware, rather than in software, and
provides an implementation example. provides an implementation example.
RFC 2525 I: "Known TCP Implementation Problems" (March 1999) RFC 2525 I: "Known TCP Implementation Problems" (March 1999)
From abstract: "This memo catalogs a number of known TCP From abstract: "This memo catalogs a number of known TCP
implementation problems. The goal in doing so is to improve implementation problems. The goal is to improve conditions in the
conditions in the existing Internet by enhancing the quality of existing Internet by enhancing the quality of current TCP/IP
current TCP/IP implementations." [RFC2525] implementations." [RFC2525]
RFC 2923 I: "TCP Problems with Path MTU Discovery" (September 2000) RFC 2923 I: "TCP Problems with Path MTU Discovery" (September 2000)
From abstract: "This memo catalogs several known Transmission From abstract: "This memo catalogs several known Transmission
Control Protocol (TCP) implementation problems dealing with Path Control Protocol (TCP) implementation problems dealing with Path
Maximum Transmission Unit Discovery (PMTUD), including the long- Maximum Transmission Unit Discovery (PMTUD), including the long-
standing black hole problem, stretch acknowledgments (ACKs) due to standing black hole problem, stretch acknowledgments (ACKs) due to
confusion between Maximum Segment Size (MSS) and segment size, and confusion between Maximum Segment Size (MSS) and segment size, and
MSS advertisement based on PMTU." [RFC2923] MSS advertisement based on PMTU." [RFC2923]
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This document [RFC6056] describes a number of simple and efficient This document [RFC6056] describes a number of simple and efficient
methods for the selection of the client port number. It reduces methods for the selection of the client port number. It reduces
the possibility of an attacker guessing the correct five-tuple the possibility of an attacker guessing the correct five-tuple
(Protocol, Source/Destination Address, Source/Destination Port). (Protocol, Source/Destination Address, Source/Destination Port).
RFC 6191 B: "Reducing the TIME-WAIT State Using TCP timestamps" RFC 6191 B: "Reducing the TIME-WAIT State Using TCP timestamps"
(April 2011) (April 2011)
This document [RFC6191] describes the usage of the TCP Timestamps This document [RFC6191] describes the usage of the TCP Timestamps
option [JBB92] to perform heuristics to determine whether or not option (RFC 1323, see Section 3.1) to perform heuristics to
to allow the creation of a new incarnation of a connection that is determine whether or not to allow the creation of a new
in the TIME-WAIT state. incarnation of a connection that is in the TIME-WAIT state.
RFC 6429 I: "TCP Sender Clarification for Persist Condition" RFC 6429 I: "TCP Sender Clarification for Persist Condition"
(December 2011) (December 2011)
This document [RFC6429] clarifies the actions that a TCP can be This document [RFC6429] clarifies the actions that a TCP can be
taken on connections that are experiencing the Zero Window Probe taken on connections that are experiencing the Zero Window Probe
(ZWP) condition. (ZWP) condition.
RFC 6897 I: "Multipath TCP (MPTCP) Application Interface RFC 6897 I: "Multipath TCP (MPTCP) Application Interface
Considerations" (March 2013) Considerations" (March 2013)
This document [RFC6897] characterizes the impact that Multipath This document [RFC6897] characterizes the impact that Multipath
TCP (MPTCP) may have on applications. It further discusses TCP (MPTCP) (see Section 4.5) may have on applications. It
compatibility issues of MPTCP in combination with non-MPTCP-aware further discusses compatibility issues of MPTCP in combination
applications. Finally, it describes a basic API that is a simple with non-MPTCP-aware applications. Finally, it describes a basic
extension of TCP's interface for MPTCP-aware applications. API that is a simple extension of TCP's interface for MPTCP-aware
applications.
7.6. Tools and Tutorials 7.6. Tools and Tutorials
RFC 1180 I: "TCP/IP Tutorial" (January 1991) (Errata) RFC 1180 I: "TCP/IP Tutorial" (January 1991) (Errata)
This document [RFC1180] is an extremely brief overview of the This document [RFC1180] is an extremely brief overview of the
TCP/IP protocol suite as a whole. It gives some explanation as to TCP/IP protocol suite as a whole. It gives some explanation as to
how and where TCP fits in. how and where TCP fits in.
RFC 1470 I: "FYI on a Network Management Tool Catalog: Tools for RFC 1470 I: "FYI on a Network Management Tool Catalog: Tools for
skipping to change at page 34, line 38 skipping to change at page 35, line 14
RFC 5783 I: "Congestion Control in the RFC Series" (February 2010) RFC 5783 I: "Congestion Control in the RFC Series" (February 2010)
This document [RFC5783] provides an overview of RFCs related to This document [RFC5783] provides an overview of RFCs related to
congestion control that have been published so far. The focus of congestion control that have been published so far. The focus of
the document is on end-host-based congestion control. the document is on end-host-based congestion control.
7.7. Management Information Bases 7.7. Management Information Bases
The first MIB module defined for use with Simple Network Management The first MIB module defined for use with Simple Network Management
Protocol (SNMP) (in RFC 1066 and its update, RFC 1156) was a single Protocol (SNMP) was a single monolithic MIB module, called MIB-I,
monolithic MIB module, called MIB-I. This evolved over time to be defined in RFC 1156. This evolved over time to the MIB-II
MIB-II (RFC 1213). It then became apparent that having a single specification in RFC 1213, which obsoletes RFC 1156. It then became
monolithic MIB module was not scalable, given the number and breadth apparent that having a single monolithic MIB module was not scalable,
of MIB data definitions that needed to be included. Thus, additional given the number and breadth of MIB data definitions that needed to
MIB modules were defined, and those parts of MIB-II that needed to be included. Thus, additional MIB modules were defined, and those
evolve were split off. Eventually, the remaining parts of MIB-II parts of MIB-II that needed to evolve were split off. Eventually,
were also split off, the TCP-specific part being documented in RFC the remaining parts of MIB-II were also split off, the TCP-specific
2012. part being documented in RFC 2012. RFC 2012 was obsoleted by RFC
4022, which is the primary TCP MIB document today. For current TCP
RFC 2012 was obsoleted by RFC 4022, which is the primary TCP MIB implementers, RFC 4022 should be supported.
document today. MIB-I, defined in RFC 1156, has been obsoleted by
the MIB-II specification in RFC 1213. For current TCP implementers,
RFC 4022 should be supported.
RFC 1066 H: "Management Information Base for Network Management of
TCP/IP-based Internets" (August 1988)
This document [RFC1066] was the description of the TCP MIB. It
was obsoleted by RFC 1156.
RFC 1156 S: "Management Information Base for Network Management of RFC 1156 S: "Management Information Base for Network Management of
TCP/IP-based Internets" (May 1990) TCP/IP-based Internets" (May 1990)
This document [RFC1156] describes the required MIB fields for TCP This document [RFC1156] describes the required MIB fields for TCP
implementations, with minor corrections and no technical changes implementations with minor corrections and no technical changes
from RFC 1066, which it obsoletes. This is the standards track from RFC 1066, which it obsoletes. This is the standards track
document for MIB-I. document for MIB-I.
RFC 1213 S: "Management Information Base for Network Management of RFC 1213 S: "Management Information Base for Network Management of
TCP/IP-based Internets: MIB-II" (March 1991) TCP/IP-based Internets: MIB-II" (March 1991)
This document [RFC1213] describes the second version of the MIB in This document [RFC1213] describes the second version of the MIB in
a monolithic form. RFC 2012 updates this document by splitting a monolithic form. It is the immediate successor of RFC 1158,
out the TCP-specific portions. with minor modifications. It obsoletes the MIB-I, defined in RFC
1156 (see Section 7.7).
RFC 2012 S: "SNMPv2 Management Information Base for the Transmission RFC 2012 S: "SNMPv2 Management Information Base for the Transmission
Control Protocol using SMIv2" (November 1996) Control Protocol using SMIv2" (November 1996)
This document [RFC2012] defined the TCP MIB, in an update to RFC In an update to RFC 1213 (see Section 7.7), this document
1213. It is now obsoleted by RFC 4022. [RFC2012] defines the TCP MIB by splitting out the TCP-specific
portions. It is now obsoleted by RFC 4022 (see Section 7.7).
RFC 2452 S: "IP Version 6 Management Information Base for the RFC 2452 S: "IP Version 6 Management Information Base for the
Transmission Control Protocol" (December 1998) Transmission Control Protocol" (December 1998)
This document [RFC2452] augments RFC 2012 by adding an IPv6- This document [RFC2452] augments RFC 2012 (see Section 7.7) by
specific connection table. The rest of 2012 holds for any IP adding an IPv6-specific connection table. The rest of RFC 2012
version. RFC 2012 is now obsoleted by RFC 4022. holds for any IP version. RFC 2452 is now obsoleted by RFC 4022
(see Section 7.7).
Although it is a standards track document, RFC 2452 is considered Although it is a standards track document, RFC 2452 is considered
a historic mistake by the MIB community, as it is based on the a historic mistake by the MIB community, as it is based on the
idea of parallel IPv4 and IPv6 structures. Although IPv6 requires idea of parallel IPv4 and IPv6 structures. Although IPv6 requires
new structures, the community has decided to define a single new structures, the community has decided to define a single
generic structure for both IPv4 and IPv6. This will aid in generic structure for both IPv4 and IPv6. This will aid in
definition, implementation, and transition between IPv4 and IPv6. definition, implementation, and transition between IPv4 and IPv6.
RFC 4022 S: "Management Information Base for the Transmission Control RFC 4022 S: "Management Information Base for the Transmission Control
Protocol (TCP)" (March 2005) Protocol (TCP)" (March 2005)
This document [RFC4022] obsoletes RFC 2012 and RFC 2452 and This document [RFC4022] obsoletes RFC 2012 (see Section 7.7) and
specifies the current standard for the TCP MIB that should be RFC 2452 (see Section 7.7) and specifies the current standard for
deployed. the TCP MIB that should be deployed.
RFC 4898 S: "TCP Extended Statistics MIB" (May 2007)
This document [RFC4898] describes extended performance statistics
for TCP. They are designed to use TCP's ideal vantage point to
diagnose performance problems in both the network and the
application.
7.8. Case Studies 7.8. Case Studies
RFC 700 U: "A Protocol Experiment" (August 1974) RFC 700 U: "A Protocol Experiment" (August 1974)
This document [RFC0700] presents a field report about the This document [RFC0700] presents a field report about the
deployment of a very early version of TCP, the so-called INWN #39 deployment of a very early version of TCP, the so-called INWN #39
protocol, which is originally described by Cerf and Kahn in INWG protocol, which is originally described by Cerf and Kahn in INWG
Note #39 [CK73] to use a PDP-11 line printer via the ARPANET. Note #39 [CK73] to use a PDP-11 line printer via the ARPANET.
skipping to change at page 37, line 25 skipping to change at page 37, line 47
Header prediction is a trick to speed up the processing of Header prediction is a trick to speed up the processing of
segments. Van Jacobson and Mike Karels developed the technique in segments. Van Jacobson and Mike Karels developed the technique in
the late 1980s. The basic idea is that some processing time can the late 1980s. The basic idea is that some processing time can
be saved when most of a segment's fields can be predicted from be saved when most of a segment's fields can be predicted from
previous segments. A good description of this was sent to the previous segments. A good description of this was sent to the
TCP-IP mailing list by Van Jacobson on March 9, 1988: TCP-IP mailing list by Van Jacobson on March 9, 1988:
"Quite a bit of the speedup comes from an algorithm that we ('we' "Quite a bit of the speedup comes from an algorithm that we ('we'
refers to collaborator Mike Karels and myself) are calling "header refers to collaborator Mike Karels and myself) are calling "header
prediction". The idea is that if you're in the middle of a bulk prediction". The idea is that if you're in the middle of a bulk
data transfer and have just seen acpacket, you know what the next data transfer and have just seen a packet, you know what the next
packet is going to look like: It will look just like the current packet is going to look like: It will look just like the current
packet with either the sequence number or ack number updated packet with either the sequence number or ack number updated
(depending on whether you're the sender or receiver). Combining (depending on whether you're the sender or receiver). Combining
this with the "Use hints" epigram from Butler Lampson's classic this with the "Use hints" epigram from Butler Lampson's classic
"Epigrams for System Designers", you start to think of the tcp "Epigrams for System Designers", you start to think of the tcp
state (rcv.nxt, snd.una, etc.) as "hints" about what the next state (rcv.nxt, snd.una, etc.) as "hints" about what the next
packet should look like. packet should look like.
If you arrange those "hints" so they match the layout of a tcp If you arrange those "hints" so they match the layout of a tcp
packet header, it takes a single 14-byte compare to see if your packet header, it takes a single 14-byte compare to see if your
skipping to change at page 38, line 8 skipping to change at page 38, line 31
set one of the unused flag bits in your header prediction to set one of the unused flag bits in your header prediction to
guarantee that the prediction will fail on the next packet and guarantee that the prediction will fail on the next packet and
force you to go through full protocol processing. Otherwise, force you to go through full protocol processing. Otherwise,
you're done with this packet. So, the *total* tcp protocol you're done with this packet. So, the *total* tcp protocol
processing, exclusive of checksumming, is on the order of 6 processing, exclusive of checksumming, is on the order of 6
compares and an add." compares and an add."
Forward Acknowledgement (FACK) Forward Acknowledgement (FACK)
FACK [MM96] includes an alternate algorithm for triggering fast FACK [MM96] includes an alternate algorithm for triggering fast
retransmit, based on the extent of the SACK scoreboard. Its goal retransmit [RFC5681], based on the extent of the SACK scoreboard.
is to trigger fast retransmit as soon as the receiver's reassembly Its goal is to trigger fast retransmit as soon as the receiver's
queue is larger than the DUPACK threshold, as indicated by the reassembly queue is larger than the duplicate ACK threshold, as
difference between the forward most SACK block edge and SND.UNA. indicated by the difference between the forward most SACK block
This algorithm quickly and reliably triggers fast retransmit in edge and SND.UNA. This algorithm quickly and reliably triggers
the presence of burst losses -- often on the first SACK following fast retransmit in the presence of burst losses -- often on the
such a loss. Such a threshold based algorithm also triggers fast first SACK following such a loss. Such a threshold based
retransmit immediately in the presence of any reordering with algorithm also triggers fast retransmit immediately in the
extent greater than the DUPACK threshold. FACK is implemented in presence of any reordering with extent greater than the duplicate
Linux and turned on per default. ACK threshold. FACK is implemented in Linux and turned on per
default.
Highspeed Congestion Control Highspeed Congestion Control
In the last decade significant research effort has been put into In the last decade significant research effort has been put into
experimental TCP congestion control modifications for obtaining experimental TCP congestion control modifications for obtaining
high throughput with reduced startup and recovery times. Only few high throughput with reduced startup and recovery times. Only few
RFCs have been published on some of these modifications, including RFCs have been published on some of these modifications, including
HighSpeed TCP [RFC3649], Limited Slow-Start [RFC3742], and Quick- HighSpeed TCP [RFC3649] (see Section 4.2), Limited Slow-Start
Start [RFC4782] (see Section 4.2), but high-rate congestion [RFC3742] (see Section 4.2), and Quick-Start [RFC4782] (see
control mechanisms are still considered an open issue in Section 4.2), but high-rate congestion control mechanisms are
congestion control research. Some other schemes have been still considered an open issue in congestion control research.
published as Internet-Drafts, e.g. CUBIC [I-D.rhee-tcpm-cubic] Some other schemes have been published as Internet-Drafts, e.g.
(the standard TCP congestion control algorithm in Linux), Compound CUBIC [I-D.rhee-tcpm-cubic] (the standard TCP congestion control
TCP [I-D.sridharan-tcpm-ctcp], and H-TCP [I-D.leith-tcp-htcp] or algorithm in Linux), Compound TCP [I-D.sridharan-tcpm-ctcp], and
have been discussed a little by the IETF, but much of the work in H-TCP [I-D.leith-tcp-htcp] or have been discussed a little by the
this area has not been adopted within the IETF yet, so the IETF, but much of the work in this area has not been adopted
majority of this work is outside the RFC series and may be within the IETF yet, so the majority of this work is outside the
discussed in other products of the IRTF Internet Congestion RFC series and may be discussed in other products of the IRTF
Control Research Group (ICCRG). Internet Congestion Control Research Group (ICCRG).
9. Security Considerations 9. Security Considerations
This document introduces no new security considerations. Each RFC This document introduces no new security considerations. Each RFC
listed in this document attempts to address the security listed in this document attempts to address the security
considerations of the specification it contains. considerations of the specification it contains.
10. IANA Considerations 10. IANA Considerations
This document contains no IANA considerations. This document contains no IANA considerations.
skipping to change at page 40, line 18 skipping to change at page 40, line 40
[RFC0889] Mills, D., "Internet delay experiments", RFC 889, [RFC0889] Mills, D., "Internet delay experiments", RFC 889,
December 1983. December 1983.
[RFC0896] Nagle, J., "Congestion control in IP/TCP internetworks", [RFC0896] Nagle, J., "Congestion control in IP/TCP internetworks",
RFC 896, January 1984. RFC 896, January 1984.
[RFC0964] Sidhu, D. and T. Blumer, "Some problems with the [RFC0964] Sidhu, D. and T. Blumer, "Some problems with the
specification of the Military Standard Transmission specification of the Military Standard Transmission
Control Protocol", RFC 964, November 1985. Control Protocol", RFC 964, November 1985.
[RFC1066] McCloghrie, K. and M. Rose, "Management Information Base
for network management of TCP/IP-based internets",
RFC 1066, August 1988.
[RFC1071] Braden, R., Borman, D., Partridge, C., and W. Plummer, [RFC1071] Braden, R., Borman, D., Partridge, C., and W. Plummer,
"Computing the Internet checksum", RFC 1071, "Computing the Internet checksum", RFC 1071,
September 1988. September 1988.
[RFC1078] Lottor, M., "TCP port service Multiplexer (TCPMUX)", [RFC1078] Lottor, M., "TCP port service Multiplexer (TCPMUX)",
RFC 1078, November 1988. RFC 1078, November 1988.
[RFC1106] Fox, R., "TCP big window and NAK options", RFC 1106, [RFC1106] Fox, R., "TCP big window and NAK options", RFC 1106,
June 1989. June 1989.
skipping to change at page 45, line 23 skipping to change at page 45, line 43
[RFC4774] Floyd, S., "Specifying Alternate Semantics for the [RFC4774] Floyd, S., "Specifying Alternate Semantics for the
Explicit Congestion Notification (ECN) Field", BCP 124, Explicit Congestion Notification (ECN) Field", BCP 124,
RFC 4774, November 2006. RFC 4774, November 2006.
[RFC4782] Floyd, S., Allman, M., Jain, A., and P. Sarolahti, "Quick- [RFC4782] Floyd, S., Allman, M., Jain, A., and P. Sarolahti, "Quick-
Start for TCP and IP", RFC 4782, January 2007. Start for TCP and IP", RFC 4782, January 2007.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU [RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821, March 2007. Discovery", RFC 4821, March 2007.
[RFC4898] Mathis, M., Heffner, J., and R. Raghunarayan, "TCP
Extended Statistics MIB", RFC 4898, May 2007.
[RFC4953] Touch, J., "Defending TCP Against Spoofing Attacks", [RFC4953] Touch, J., "Defending TCP Against Spoofing Attacks",
RFC 4953, July 2007. RFC 4953, July 2007.
[RFC4987] Eddy, W., "TCP SYN Flooding Attacks and Common [RFC4987] Eddy, W., "TCP SYN Flooding Attacks and Common
Mitigations", RFC 4987, August 2007. Mitigations", RFC 4987, August 2007.
[RFC5033] Floyd, S. and M. Allman, "Specifying New Congestion [RFC5033] Floyd, S. and M. Allman, "Specifying New Congestion
Control Algorithms", BCP 133, RFC 5033, August 2007. Control Algorithms", BCP 133, RFC 5033, August 2007.
[RFC5166] Floyd, S., "Metrics for the Evaluation of Congestion [RFC5166] Floyd, S., "Metrics for the Evaluation of Congestion
skipping to change at page 49, line 35 skipping to change at page 50, line 12
Proceedings, in ACM Computer Communication Review 26 (4), Proceedings, in ACM Computer Communication Review 26 (4),
pp. 281-292, October 1996. pp. 281-292, October 1996.
[RFC1016] Prue, W. and J. Postel, "Something a host could do with [RFC1016] Prue, W. and J. Postel, "Something a host could do with
source quench: The Source Quench Introduced Delay source quench: The Source Quench Introduced Delay
(SQuID)", RFC 1016, July 1987. (SQuID)", RFC 1016, July 1987.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision [RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, October 1996. 3", BCP 9, RFC 2026, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS "Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, Field) in the IPv4 and IPv6 Headers", RFC 2474,
December 1998. December 1998.
[RFC3758] Stewart, R., Ramalho, M., Xie, Q., Tuexen, M., and P.
Conrad, "Stream Control Transmission Protocol (SCTP)
Partial Reliability Extension", RFC 3758, May 2004.
[RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram [RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram
Congestion Control Protocol (DCCP)", RFC 4340, March 2006. Congestion Control Protocol (DCCP)", RFC 4340, March 2006.
[RFC4341] Floyd, S. and E. Kohler, "Profile for Datagram Congestion [RFC4341] Floyd, S. and E. Kohler, "Profile for Datagram Congestion
Control Protocol (DCCP) Congestion Control ID 2: TCP-like Control Protocol (DCCP) Congestion Control ID 2: TCP-like
Congestion Control", RFC 4341, March 2006. Congestion Control", RFC 4341, March 2006.
[RFC6115] Li, T., "Recommendation for a Routing Architecture",
RFC 6115, February 2011.
[SCWA99] Savage, S., Cardwell, N., Wetherall, D., and T. Anderson, [SCWA99] Savage, S., Cardwell, N., Wetherall, D., and T. Anderson,
"TCP Congestion Control with a Misbehaving Receiver", ACM "TCP Congestion Control with a Misbehaving Receiver", ACM
Computer Communication Review, 29 (5), pp. 71-78, Computer Communication Review, 29 (5), pp. 71-78,
October 1999. October 1999.
Authors' Addresses Authors' Addresses
Martin Duke Martin Duke
F5 Networks F5 Networks
401 Elliott Ave W 401 Elliott Ave W
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