Network Working Group M. Duke
Internet-Draft Boeing Phantom Works
Expires: July 21, 2005 R. Braden
USC Information Sciences Institute
W. Eddy
NASA GRC/Verizon FNS
E. Blanton
Purdue University
January 20, 2005
A Roadmap for TCP Specification Documents
draft-ietf-tcpm-tcp-roadmap-01
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document contains a "roadmap" to the Requests for Comments (RFC)
documents relating to the Internet's Transmission Control Protocol
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(TCP). This roadmap provides a brief summary of the documents
defining TCP and various TCP extensions that have accumulated in the
RFC series. This serves as a guide and quick reference for both TCP
implementers and other parties who desire information contained in
the TCP-related RFCs.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Basic Functionality . . . . . . . . . . . . . . . . . . . . . 5
3. Standard Enhancements . . . . . . . . . . . . . . . . . . . . 7
3.1 Congestion Control and Loss Recovery Extensions . . . . . 7
3.2 SACK-based Loss Recovery and Congestion Control . . . . . 9
3.3 Dealing with Forged Segments . . . . . . . . . . . . . . . 9
4. Experimental Extensions . . . . . . . . . . . . . . . . . . . 11
5. Historic Extensions . . . . . . . . . . . . . . . . . . . . . 13
6. Support Documents . . . . . . . . . . . . . . . . . . . . . . 15
6.1 Foundational Works . . . . . . . . . . . . . . . . . . . . 15
6.2 Difficult Network Environments . . . . . . . . . . . . . . 16
6.3 Implementation Advice . . . . . . . . . . . . . . . . . . 18
6.4 Management Information Bases . . . . . . . . . . . . . . . 19
6.5 Tools and Tutorials . . . . . . . . . . . . . . . . . . . 20
6.6 Case Studies . . . . . . . . . . . . . . . . . . . . . . . 21
7. Security Considerations . . . . . . . . . . . . . . . . . . . 23
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 25
9.1 Basic Functionality . . . . . . . . . . . . . . . . . . . 25
9.2 Standard Enhancements . . . . . . . . . . . . . . . . . . 25
9.3 Experimental Extensions . . . . . . . . . . . . . . . . . 26
9.4 Historic Extensions . . . . . . . . . . . . . . . . . . . 27
9.5 Support Documents . . . . . . . . . . . . . . . . . . . . 27
9.6 Informative References Outside the RFC Series . . . . . . 30
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 30
Intellectual Property and Copyright Statements . . . . . . . . 32
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1. Introduction
A correct and efficient implementation of the Transmission Control
Protocol (TCP) [RFC0793] is a critical part of the software of most
Internet hosts. As TCP has evolved over the years, many distinct
documents have become part of the accepted standard for TCP. At the
same time, a large number of more experimental modifications to TCP
have also been published in the RFC series, along with informational
notes, case studies, and other advice.
As an introduction to newcomers and an attempt to organize the
plethora of information for old hands, this document contains a
"roadmap" to the TCP-related RFCs. It provides a brief summary of
the RFC documents that define TCP. This should provide guidance to
implementers on the relevance and significance of the standards track
extensions, informational notes, and best current practices that
relate to TCP.
This roadmap includes a brief description of the contents of each
TCP-related RFC. In some cases, we simply supply the abstract or a
key summary sentence from the text as a terse description. In
addition, a letter code after each RFC number indicates its category
in the RFC series:
S - Standards Track (Proposed Standard, Draft Standard, or
Standard)
E - Experimental
B - Best Current Practice
I - Informational
Note that the category of an RFC does not necessarily reflect its
current relevance. For instance, RFC 2581 is nearly universally
deployed although it is only a Proposed Standard. Similarly, some
Informational RFCs contain significant technical proposals for
changing TCP.
This roadmap is divided into four main sections. Section 2 lists the
RFCs that describe absolutely required TCP behaviors for proper
functioning and interoperability. Further RFCs that describe
strongly encouraged, but not essential, behaviors are listed in
Section 3. Experimental extensions which are not yet standard
practices, but potentially could be in the future, are described in
Section 4.
The reader probably notices that these three sections are broadly
equivalent to MUST/SHOULD/MAY specifications, and while the authors
support this intuition, this document is merely descriptive; it does
not represent a binding standards track position. An individual
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implementor still needs to examine the standards documents themselves
to evaluate specific requirement levels.
A small number of older experimental extensions which have not caught
on are noted in Section 5. Many other supporting documents that are
relevant to the development, implementation, and deployment of TCP
are described in Section 6. Within each section, RFCs are listed in
chronological order.
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2. Basic Functionality
A small number of documents compose the core specification of TCP.
These define the required basic functionalities of TCP's header
parsing, state machine, congestion control, and retransmission
timeout computation. These base specifications must be correctly
followed for interoperability.
RFC 793 S: "Transmission Control Protocol", STD 7 (September 1981)
This is the fundamental TCP specification document [RFC0793].
Written by Jon Postel as part of the Internet protocol suite's
core, it describes the TCP packet format, the TCP state machine
and event processing, and TCP's semantics for data transmission,
reliability, flow control, multiplexing, and acknowledgement.
Section 3.6 of RFC 793, describing TCP's handling of the IP
precedence and security compartment, is mostly irrelevant today.
RFC 2873 changed the IP precedence handling, and the security
compartment portion of the API is no longer implemented or used.
In addition, RFC 793 did not describe any congestion control
mechanism. Otherwise, however, the majority of this document
still acurately describes modern TCPs. RFC 793 is the last of a
series of developmental TCP specifications, starting from IENs and
continuing in the RFC series.
RFC 1122 S: "Requirements for Internet Hosts - Communication Layers"
(October 1989)
This document [RFC1122] updates and clarifies RFC 793, fixing some
specification bugs and oversights. It also explains some features
such as keep-alives and Karn's and Jacobson's RTO estimation
algorithms [Karn][VJ88]. ICMP interactions are mentioned and some
tips are given for efficient implementation. RFC 1122 is an
Applicability Statement, listing the various features that MUST,
SHOULD, MAY, SHOULD NOT, and MUST NOT be present in
standards-conforming TCP implementations.
RFC 2147 S: "TCP and UDP over IPv6 Jumbograms" (May 1997)
IPv6's support for longer datagrams than were allowed in IPv4,
necessitated some changes to the way that TCP's MSS and Urgent
fields (both 16 bits) are treated.
RFC 2460 S: "Internet Protocol, Version 6 (IPv6) Specification
(December 1998)
This document [RFC2460] makes a slight update to the way the
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pseudo-header for checksum computation is derived, defining the
process for IPv6 in addition to the previous practice for IPv4.
RFC 2581 S: "TCP Congestion Control" (April 1999)
Although RFC 793 did not contain any congestion control
mechanisms, today congestion control is a required component of
TCP implementations. This document [RFC2581] defines the current
versions of Van Jacobson's congestion avoidance and control
mechanisms for TCP, based on his 1988 SIGCOMM paper [VJ88]. RFC
2001 was a conceptual precursor that was obsoleted by RFC 2581.
A number of behaviors that together comprise what the community
refers to as "Reno TCP", are described in RFC 2581. The name
"Reno" comes from the Net/2 release of the 4.3 BSD operating
system. This is generally regarded as the least common
denominator among TCP flavors currently found running on Internet
hosts. Reno TCP includes the congestion control features of slow
start, congestion avoidance, fast retransmit, and fast recovery.
RFC 2873 S: "TCP Processing of the IPv4 Precendence Field" (June
2000)
This document [RFC2873] removes from the TCP specification all
processing of the precedence bits of the TOS byte of the IP
header. This resolves a conflict over the use of these bits
between RFC 793 and Differentiated Services.
RFC 2988 S: "Computing TCP's Retransmission Timer" (November 2000)
Abstract: "This document defines the standard algorithm that
Transmission Control Protocol (TCP) senders are required to use to
compute and manage their retransmission timer. It expands on the
discussion in section 4.2.3.1 of RFC 1122 and upgrades the
requirement of supporting the algorithm from a SHOULD to a MUST."
[RFC2988]
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3. Standard Enhancements
This section describes recommended TCP modifications that improve
performance and security. RFCs 1323 and 3168 represent fundamental
changes to the protocol. RFC 1323, based on RFCs 1072 and 1185,
allows better utilization of high bandwidth-delay product paths by
providing some needed mechanisms for high-rate transfers. RFC 3168
describes a change to the Internet's architecture, where routers
signal end-hosts of growing congestion levels, and can do so before
packet losses are forced. Section 3.1 lists improvements in the
congestion control and loss recovery mechanisms specified in RFC
2581. Section 3.2 describes further refinements that make use of
selective acknowledgements. Section 3.3 deals with the problem of
preventing forged segments.
RFC 1323 S: "TCP Extensions for High Performance" (May 1992)
This document [RFC1323] defines TCP extensions for window scaling,
timestamps, and protection against wrapped sequence numbers, for
efficient and safe operation over paths with large bandwidth-delay
products. These extensions are commonly found in currently-used
systems; however, they may require manual tuning and
configuration. Some "corner cases" in this specification are
still under discussion.
RFC 3168 S: "The Addition of Explicit Congestion Notification (ECN)
to IP" (September 2001)
This document [RFC3168] defines a means of detecting congestion
without resorting to packet loss. Although congestion
notification takes place at the IP level, ECN 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 define two
previously-unused flag bits in the TCP header for ECN support.
RFC 3540 provides a supplementary (experimental) means for making
ECN use more secure, and RFC 2884 provides some sample results
from using ECN.
3.1 Congestion Control and Loss Recovery Extensions
Two of the most important aspects of TCP are its congestion control
and loss recovery features. Since TCP traditionally (in the absence
of ECN) uses losses to infer congestion, there is a rather intimate
coupling between congestion control and loss recovery mechanisms.
There are several extensions to both features, and more often than
not, a particular extension applies to both. In this sub-section, we
group enhancements to either congestion control, loss recovery, or
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both, which can be performed unilaterally - without negotiating
support between endpoints. In the next sub-section, we group the
extensions which specify or rely on the SACK option, whose use must
be negotiated bilaterally. TCP implementations should include the
enhancements from both sub-sections so that they can perform well
without regard to the feature sets of other hosts they connect to.
For example, if SACK use is not successfully negotiated, a TCP should
use the NewReno behavior as a fall-back.
RFC 3042 S: "Enhancing TCP's Loss Recovery Using Limited Transmit"
(January 2001)
Abstract: "This document proposes [Limited Transmit,] a new
Transmission Control Protocol (TCP) mechanism that can be used to
more effectively recover lost segments when a connection's
congestion window is small, or when a large number of segments are
lost in a single transmission window." [RFC3042]
RFC 3390 S: "Increasing TCP'S Initial Window" (October 2002)
This document [RFC3390] updates RFC 2581 to permit an initial TCP
window larger that one packet during in the slow-start phase.
RFC 3782 S: "The NewReno Modification to TCP's Fast Recovery
Algorithm" (April 2004)
This document [RFC3782] specifies a slight modification to the
standard Reno fast recovery algorithm, whereby a TCP sender can
use partial acknowledgements to make inferences determining the
next segment to send in situations where SACK would be helpful,
but isn't available.
Work in progress: The Eifel Response Algorithm for TCP (Internet
Draft name: draft-ietf-tsvwg-tcp-eifel-response)
At the time of this writing, work on this document (from authors
Reiner Ludwig and Andrei Gurtov) had stabilized within the
Transport Area Working Group, and the document was planned to
become a Proposed Standard, pending IESG review, but was not yet a
part of the RFC series. This document describes the response
portion of the Eifel algorithm, which can be used in conjunction
with one of several methods of detecting when loss recovery has
been spuriously entered, such as the Eifel detection algorithm in
RFC 3522, the algorithm in RFC 3708, or F-RTO.
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Abstract: "Based on an appropriate detection algorithm, the Eifel
response algorithm provides a way for a TCP sender to respond to a
detected spurious timeout. It adapts the retransmission timer to
avoid further spurious timeouts, and can avoid - depending on the
detection algorithm - the often unnecessary go-back-N retransmits
that would otherwise be sent. In addition, the Eifel response
algorithm restores the congestion control state in such a way that
packet bursts are avoided."
3.2 SACK-based Loss Recovery and Congestion Control
The base TCP specification in RFC 793 provided only a simple
cumulative acknowledgment mechanism. However, a selective
acknowledgment (SACK) mechanism provides significant performance
improvement in the presence of packet losses, more than outweighing
the modest increase in complexity. A TCP should be expected to
implement SACK, however SACK is a negotiated option and is only used
if support is advertised by both sides of a connection.
RFC 2018 S: "TCP Selective Acknowledgement Options" (October 1996)
This document [RFC2018] defines the basic selective
acknowledgement (SACK) mechanism for TCP.
RFC 2883 S: "An Extension to the Selective Acknowledgement (SACK)
Option for TCP" (July 2000)
This document [RFC2883] extends RFC 2018 to cover the case of
acknowledging duplicate packets.
RFC 3517 S: "A Conservative Selective Acknowledgement (SACK)-based
Loss Recovery Algorithm for TCP" (April 2003)
This document [RFC3517] describes a relatively sophisticated
algorithm that a TCP sender can use for loss recovery when SACK
reports more than one segment lost from a single flight of data.
While support for the exchange of SACK information is widely
implemented, not all implementations use an algorithm as
sophisticated as that described in RFC 3517.
3.3 Dealing with Forged Segments
By default, TCP lacks any cryptographic structures to differentiate
legitimate segments and those spoofed from malicious hosts. Spoofing
valid segments requires correctly guessing a number of fields. The
documents in this sub-section describe ways to make that guessing
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harder, or prevent it from being able to negatively impact a
connection.
RFC 1948 I: "Defending Against Sequence Number Attacks" (May 1996)
This document [RFC1948] describes the TCP vulnerability based upon
guessing sequence numbers and as well as defenses against this
exploit. Some variation is implemented in most currently-used
operating systems.
RFC 2385 S: "Protection of BGP Sessions via the TCP MD5 Signature
Option" (August 1998)
From document: "This document describes currrent existing practice
for securing BGP against certain simple attacks. It is understood
to have security weaknesses against concerted attacks.
This memo describes a TCP extension to enhance security for BGP.
It defines a new TCP option for carrying an MD5 [RFC1321] digest
in a TCP segment. This digest acts like a signature for that
segment, incorporating information known only to the connection
end points. Since BGP uses TCP as its transport, using this
option in the way described in this paper significantly reduces
the danger from certain security attacks on BGP." [RFC2385]
TCP MD5 options are currently only used in very limited contexts,
primarily for defending BGP exchanges between routers. Some
deployment notes for those using TCP MD5 are found in the later
RFC 3562, "Key Management Considerations for the TCP MD5 Signature
Option" [RFC3562].
Work in progress: Transmission Control Protocol Security
Considerations (Internet Draft name: draft-ietf-tcpm-tcpsecure)
At the time of this writing, the TCP Maintenance and Minor
Extensions Working Group is producing a document (edited by Mitesh
Dalal) which describes a challenge-response mechanism for securing
TCP against spoofed control segments. This document is expected
to become an RFC in the near future.
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4. Experimental Extensions
The RFCs in this section are still experimental, but may become
proposed standards in the future. At least part of the reason that
they are still experimental is to gain more wide-scale experience
with them before making a standards track decision.
RFC 2140 I: "TCP Control Block Interdependence" (April 1997)
This document [RFC2140] suggests how TCP connections between the
same endpoints might share information, such as their congestion
control state. To some degree, this is done in practice by a few
operating systems; for example, Linux has a destination cache.
A related proposal, the Congestion Manager, is specified in RFC
3124 [RFC3124]. The idea behind the Congestion Manager, moving
congestion control outside of individual TCP connections,
represents a modification to the core of TCP. Although a Proposed
Standard, some pieces of the Congestion Manager support
architecture have not been specified yet, and it has not achieved
use or implementation beyond experimental stacks.
RFC 2861 E: "TCP Congestion Window Validation" (June 2000)
This document [RFC2861] suggests reducing the congestion window
over time when no packets are flowing.
RFC 3465 E: "TCP Congestion Control with Appropriate Byte Counting
(ABC)" (February 2003)
This document [RFC3465] suggests that congestion control use the
number of bytes acknowledged rather than the number of
acknowledgements received. This has been implemented in Linux.
The ABC mechanism behaves differently than the standard means when
there is not a one-to-one relationship between data segments and
acknowledgements. ABC still operates within the accepted
guidelines, but is more robust to delayed ACKs and ACK-division
[Savage].
RFC 3522 E: "The Eifel Detection Algorithm for TCP" (April 2003)
This document [RFC3522] suggests using timestamps to detect
spurious timeouts.
RFC 3540 E: "Robust Explicit Congestion Notification (ECN) signaling
with Nonces" (June 2003)
This document [RFC3540] suggests a modified ECN to address
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security concerns, and updates RFC 3168.
RFC 3649 E: "HighSpeed TCP for Large Congestion Windows" (December
2003)
This document [RFC3649] suggests a modification to TCP's
steady-state behavior to efficiently use very large windows.
RFC 3708 E: "Using TCP Duplicate Selective Acknowledgement (DSACKs)
and Stream Control Transmission Protocol (SCTP) Duplicate
Transmission Sequence Numbers (TSNs) to Detect Spurious
Retransmissions" (February 2004)
Abstract: "TCP and Stream Control Transmission Protocol (SCTP)
provide notification of duplicate segment receipt through
Duplicate Selective Acknowledgement (DSACKs) and Duplicate
Transmission Sequence Number (TSN) notification, respectively.
This document presents conservative methods of using this
information to identify unnecessary retransmissions for various
applications." [RFC3708]
RFC 3742 E: "Limited Slow-Start for TCP with Large Congestion
Windows" (March 2004)
This document [RFC3742] describes a more conservative slow-start
behavior to prevent massive packet losses when a connection uses a
very large window.
Work in progress: Forward RTO-Recovery (F-RTO): An Algorithm for
Detecting Spurious Retransmission Timeouts with TCP and SCTP
(Internet Draft name: draft-ietf-tcpm-frto)
The F-RTO detection algorithm provides another option for
inferring spurious retransmission timeouts. At the time of this
writing, the TCP Maintenance and Minor Extensions Working Group
had completed a document describing F-RTO (by Pasi Sarolahti and
Markku Kojo), and planned to make this an Experimental part of the
RFC series, pending IESG review.
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5. Historic Extensions
The RFCs listed here define extensions that have thus far failed to
arouse substantial interest, or were found to be defective.
RFC 1106 "TCP Big Window and NAK Options" (June 1989)
This RFC [RFC1106] defined an alternative to the Window Scale
option for using large windows, and described the "negative
acknowledgement" or NAK option. There is a comparison of NAK and
SACK methods, and early discussion of TCP over satellite issues.
The options described in this document have not been adopted by
the larger community, although NAKs are used in the SCPS-TP
adaptation of TCP, developed by the Consultive Committee for Space
Data Systems (CCSDS).
RFC 1110 "A Problem with the TCP Big Window Option" (August 1989)
Abstract: "The TCP Big Window option discussed in RFC 1106 will
not work properly in an Internet environment which has both a high
bandwidth * delay product and the possibility of disordering and
duplicating packets. In such networks, the window size must not
be increased without a similar increase in the sequence number
space. Therefore, a different approach to big windows should be
taken in the Internet." [RFC1110]
RFC 1146 E "TCP Alternate Checksum Options" (March 1990)
This document [RFC1146] defined more robust TCP checksums than the
16-bit ones-complement in use today. A typographical error in RFC
1145 is fixed in RFC 1146, otherwise the documents are the same.
RFC 1263 "TCP Extensions Considered Harmful" (October 1991)
This interesting document [RFC1263] argues against "backwards
compatible" TCP extensions. Specifically mentioned are several
TCP enhancements that have been successful, including timestamps,
window scaling, PAWS, and SACK. RFC 1263 presents an alternative
approach called "protocol evolution", whereby several evolutionary
versions of TCP would exist on hosts. These distinct TCP versions
would represent upgrades to each other and could be
header-incompatible. Interoperability would be provided by having
a virtualization layer select the right TCP version for a
particular connection. This idea did not catch on with the
community, while the type of extensions RFC 1263 specifically
targeted as harmful did become popular.
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RFC 1379 I "Extending TCP for Transactions -- Concepts" (November
1992)
See RFC 1644.
RFC 1644 E "T/TCP -- TCP Extensions for Transactions Functional
Specification" (July 1994)
The inventors of TCP believed that cached connection state could
have been used to eliminate TCP's 3-way handshake, to support
two-packet request/response exchanges. RFCs 1379 [RFC1379] and
1644 [RFC1644] show that this is far from simple. Furthermore,
T/TCP floundered on the ease of denial-of-service attacks that can
result.
RFC 1693 E "An Extension to TCP: Partial Order Service" (November
1994)
This document [RFC1693] defines a TCP extension for applications
that do not care about the order in which application-layer
objects are received. Examples are multimedia and database
applications. In practice, these applications either accept the
possible performance loss because of TCP's strict ordering, or
they use more specialized transport protocols.
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6. Support Documents
This section contains several classes of documents that do not
necessarily define current protocol behaviors, but are nevertheless
of interest to TCP implementors. Section 6.1 describes several
foundational RFCs that give modern readers a better understanding of
the principles underlying TCP's behaviors and development over the
years. The documents listed in Section 6.2 provide advice on using
TCP in various types of network situations that pose challenges above
those of typical wired links. Some implementation notes can be found
in Section 6.3. The TCP Management Information Bases are described
in Section 6.4. RFCs that describe tools for testing and debugging
TCP implementations or contain high-level tutorials on the protocol
are listed Section 6.5, while Section 6.6 lists a number of case
studies that have explored TCP performance.
6.1 Foundational Works
The documents listed in this section contain information that is
largely duplicated by the standards documents previously discussed.
However, some of them contain a greater depth of problem statement
explanation or other context. Particularly, RFCs 813-817 (known as
the "Dave Clark Five"), describe some early problems and solutions
(RFC 815 only describes the reassembly of IP fragments, and is not
included here).
RFC 813: "Window and Acknowledgement Strategy in TCP" (July 1982)
This document [RFC0813] contains an early discussion of Silly
Window Syndrome and its avoidance, and motivates and describes the
use of delayed acknowledgements.
RFC 814: "Name, Addresses, Ports, and Routes" (July 1982)
Suggestions and guidance for the design of tables and algorithms
to keep track of various identifiers within a TCP/IP
implementation are provided by this document [RFC0814].
RFC 816: "Fault Isolation and Recovery" (July 1982)
In this document [RFC0816], TCP's response to indications of
network error conditions such as timeouts or received ICMP
messages.
RFC 817: "Modularity and Efficiency in Protocol Implementation" (July
1982)
This document [RFC0817] contains implementation suggestions that
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are general and not TCP-specific. However they have been used to
develop TCP implementations and describe some performance
implications of the interactions between various layers in the
Internet stack.
RFC 872: "TCP-ON-A-LAN" (September 1982)
Conclusion: "The sometimes-expressed fear that using TCP on a
local net is a bad idea is unfounded." [RFC0872]
RFC 896: "Congestion Control in IP/TCP Internetworks" (January 1984)
This document [RFC0896] contains some early experiences with
congestion collapse and some initial thoughts on how to avoid it
using congestion control in TCP.
RFC 964: "Some Problems with the Specification of the Military
Standard Transmission Control Protocol" (November 1985)
This document [RFC0964] was prepared by the US Military to define
TCP in greater detail than RFC 793. A few serious specification
bugs are detailed in RFC 964, reminding us of the difficulty in
specification writing (even when working from existing
documents!).
RFC 1072: "TCP Extensions for Long-Delay Paths" (October 1988)
This document [RFC1072] contains early explanations of the
mechanisms that were later described by RFCs 1323 and 2018, which
obsolete it.
RFC 1185: "TCP Extension for High-Speed Paths" (October 1990)
This document [RFC1185] builds on RFC 1072 to describe more
advanced strategies for dealing with sequence number wrapping and
detecting duplicates from earlier connections. This document was
obsoleted by RFC 1323.
RFC 2914 B: "Congestion Control Principles" (September 2000)
This document [RFC2914] motivates the use of end-to-end congestion
control for preventing congestion collapse and providing fairness
to TCP.
6.2 Difficult Network Environments
As the internetworking field has explored wireless, satellite,
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cellular telephone, and other kinds of link-layer technologies, a
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
challenging network environments and how TCP interacts with them.
RFC 2488 B: "Enhancing TCP Over Satellite Channels using Standard
Mechanisms" (January 1999)
From abstract: "While TCP works over satellite channels there are
several IETF standardized mechanisms that enable TCP to more
effectively utilize the available capacity of the network path.
This document outlines some of these TCP mitigations. At this
time, all mitigations discussed in this document are IETF
standards track mechanisms (or are compliant with IETF
standards)." [RFC2488]
RFC 2757 I: "Long Thin Networks" (January 2000)
Several methods of improving TCP performance over long thin
networks, such as geosynchronous satellite links, are discussed in
this document [RFC2757]. A particular set of TCP options is
developed that should work well in such environments, and be safe
to use in the global Internet.
RFC 2760 I: "Ongoing TCP Research Related to Satellites" (February
2000)
This document [RFC2760] discusses the advantages and disadvantages
of several different experimental means of improving TCP
performance over long-delay or error-prone paths. These include:
T/TCP, larger initial windows, byte counting, delayed
acknowledgements, slow start thresholds, NewReno and SACK-based
loss recovery, FACK [FACK], ECN, various corruption-detection
mechanisms, congestion avoidance changes for fairness, use of
multiple parallel flows, pacing, header compression, state
sharing, and ACK congestion control, filtering, and
reconstruction. While RFC 2488 looks at standard extensions, this
document focuses on more experimental means of performance
enhancement.
RFC 3135 I: "Performance Enhancing Proxies Intended to Mitigate
Link-Related Degradations" (June 2001)
From abstract: "This document is a survey of Performance Enhancing
Proxies (PEPs) often employed to improve degraded TCP performance
caused by characteristics of specific link environments, for
example, in satellite, wireless WAN, and wireless LAN
environments. Different types of Performance Enhancing Proxies
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are described as well as the mechanisms used to improve
performance." [RFC3135]
RFC 3449 B: "TCP Performance Implications of Network Path Asymmetry"
(December 2002)
From abstract: "This document describes TCP performance problems
that arise because of asymmetric effects. These problems arise in
several access networks, including bandwidth-asymmetric networks
and packet radio subnetworks, for different underlying reasons.
However, the end result on TCP performance is the same in both
cases: performance often degrades significantly because of
imperfection and variability in the ACK feedback from the receiver
to the sender.
The document details several mitigations to these effects, which
have either been proposed or evaluated in the literature, or are
currently deployed in networks." [RFC3449]
RFC 3481 B: "TCP over Second (2.5G) and Third (3G) Generation
Wireless Networks" (February 2003)
From abstract: "This document describes a profile for optimizing
TCP to adapt so that it handles paths including second (2.5G) and
third (3G) generation wireless networks." [RFC3481]
RFC 3819 B: "Advice for Internet Subnetwork Designers" (July 2004)
This document [RFC3819] describes how TCP performance can be
negatively impacted by some particular lower-layer behaviors, and
provides guidance in designing lower-layer networks and protocols
to be amicable to TCP.
6.3 Implementation Advice
RFC 879: "The TCP Maximum Segment Size and Related Topics" (November
1983)
Abstract: 'This memo discusses the TCP Maximum Segment Size Option
and related topics. The purposes is to clarify some aspects of
TCP and its interaction with IP. This memo is a clarification to
the TCP specification, and contains information that may be
considered as "advice to implementers".' [RFC0879]
RFC 2525 I: "Known TCP Implementation Problems" (March 1999)
From abstract: "This memo catalogs a number of known TCP
implementation problems. The goal in doing so is to improve
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conditions in the existing Internet by enhancing the quality of
current TCP/IP implementations." [RFC2525]
RFC 2923 I: "TCP Problems with Path MTU Discovery" (September 2000)
From abstract: "This memo catalogs several known Transmission
Control Protocol (TCP) implementation problems dealing with Path
Maximum Transmission Unit Discovery (PMTUD), including the
long-standing black hole problem, stretch acknowlegements (ACKs)
due to confusion between Maximum Segment Size (MSS) and segment
size, and MSS advertisement based on PMTU." [RFC2923]
RFC 3360 B: "Inappropriate TCP Resets Considered Harmful" (August
2002)
This document [RFC3360] is a plea that firewall vendors not send
gratuitous TCP RST (Reset) packets when unassigned TCP header bits
are used. This practice prevents desirable extension and
evolution of the protocol and hence is inimical to the future of
the Internet.
RFC 3493 I: "Basic Socket Interface Extensions for IPv6" (February
2003)
This document [RFC3493] describes the de facto standard sockets
API for programming with TCP. This API is implemented nearly
ubiquitously in modern operating systems and programming
languages.
6.4 Management Information Bases
The first MIB module defined for use with SNMP (in RFC 1066 and its
update, RFC 1156) was a single monolithic MIB module, called MIB-I.
This evolved over time to be MIB-II (RFC 1213). It then became
apparent that having a single monolithic MIB module was not scalable,
given the number and breadth of MIB data definitions that needed to
be included. Thus, additional MIB modules were defined, and those
parts of MIB-II which needed to evolve were split off. Eventually,
the remaining parts of MIB-II were also split off, with the
TCP-specific part being documented in RFC 2012.
RFC 2012 is the primary document for MIB-II. MIB-I, defined in RFC
1156, has been obsoleted by the MIB-II specification in RFC 1213
(updated by 2012). Work is in progress, at the time of this writing,
on a document that incorporates IPv6 and updates and obsoletes RFC
2012 (currently in the form of draft-ietf-ipv6-rfc2012-update, edited
by Rajiv Raghunarayan, under submission to the IESG as a Proposed
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Standard).
RFC 1066: "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
TCP/IP-based Internets" (May 1990)
This document [RFC1156] describes the required MIB fields for TCP
implementations, with minor corrections and no technical changes
from RFC 1066, which it obsoletes. This is the standards track
document for MIB-I.
RFC 1213 S: "Management Information Base for Network Management of
TCP/IP-based Internets: MIB-II" (March 1991)
This document [RFC1213] describes the second version of the MIB in
a monolithic form. RFC 2012 updates this document by splitting
out the TCP-specific portions.
RFC 2012 S: "SNMPv2 Management Information Base for the Transmission
Control Protocol using SMIv2" (November 1996)
This document [RFC2012] defines the TCP MIB, updating RFC 1213.
RFC 2452 S: "IP Version 6 Management Information Base for the
Transmission Control Protocol" (December 1998)
This document [RFC2452] augments RFC 2012 by adding an
IPv6-specific connection table. The rest of 2012 holds for any IP
version.
Although it is a standards track document, RFC 2452 is considered
a historic mistake by the MIB community, as it is based on the
idea of parallel IPv4 and IPv6 structures. Although IPv6 requires
new structures, the community has decided to define a single
generic structure for both IPv4 and IPv6. This will aid in
definition, implementation, and transition between IPv4 and IPv6.
6.5 Tools and Tutorials
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RFC 1180 I: "TCP/IP Tutorial" (January 1991)
This document [RFC1180] is an extremely brief overview of the
TCP/IP protocol suite as a whole. It gives some explanation as to
how and where TCP fits in.
RFC 1470 I: "FYI on a Network Management Tool Catalog: Tools for
Monitoring and Debugging TCP/IP Internets and Interconnected Devices"
(June 1993)
A few of the tools that this document [RFC1470] describes are
still maintained and in use today, for example ttcp and tcpdump.
However, many of the tools described do not relate specifically to
TCP and are no longer used or easily available.
RFC 2398 I: "Some Testing Tools for TCP Implementors" (August 1998)
This document [RFC2398] describes a number of TCP packet
generation and analysis tools. While some of these tools are no
longer readily available or widely used, for the most part they
are still relevant and useable.
6.6 Case Studies
RFC 1337 I: "TIME-WAIT Assassination Hazards in TCP" (May 1992)
This document [RFC1337] points out a problem with acting on
received reset segments while in the TIME-WAIT state. The main
recemmendation is that hosts in TIME-WAIT ignore resets.
RFC 2415 I: "Simulation Studies of Increased Initial TCP Window Size"
(September 1998)
This document [RFC2415] presents results of some simulations using
TCP initial windows greater than 1 segment. The analysis
indicates that user-perceived performance can be improved by
increasing the initial window to 3 segments.
RFC 2416 I: "When TCP Starts Up With Four Packets Into Only Three
Buffers" (September 1998)
This document [RFC2416] uses simulation results to clear up some
concerns about using an initial window of 4 segments when the
network path has less provisioning.
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RFC 2884 I: "Performance Evaluation of Explicit Congestion
Notification (ECN) in IP Networks" (July 2000)
This document [RFC2884] describes experimental results that show
some improvements to the performance of both short and long-lived
connections due to ECN.
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7. Security Considerations
This document introduces no new security considerations. Each RFC
listed in this document attempts to address the security
considerations of the specification it contains.
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8. Acknowledgments
This document grew out of a discussion on the end2end-interest
mailing list, the public list of the End-to-End Research Group of the
IRTF. We thank Joe Touch, Reiner Ludwig, and Pekka Savola for their
contributions, in particular. The chairs of the TCPM working group,
Mark Allman and Ted Faber, have been instrumental in the development
of this document. Keith McCloghrie provided some useful notes and
clarification on the various MIB-related RFCs.
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9. References
9.1 Basic Functionality
[RFC0793] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, September 1981.
[RFC1122] Braden, R., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, October 1989.
[RFC2147] Borman, D., "TCP and UDP over IPv6 Jumbograms", RFC 2147,
May 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2581] Allman, M., Paxson, V. and W. Stevens, "TCP Congestion
Control", RFC 2581, April 1999.
[RFC2873] Xiao, X., Hannan, A., Paxson, V. and E. Crabbe, "TCP
Processing of the IPv4 Precedence Field", RFC 2873, June
2000.
[RFC2988] Paxson, V. and M. Allman, "Computing TCP's Retransmission
Timer", RFC 2988, November 2000.
9.2 Standard Enhancements
[RFC1323] Jacobson, V., Braden, B. and D. Borman, "TCP Extensions
for High Performance", RFC 1323, May 1992.
[RFC1948] Bellovin, S., "Defending Against Sequence Number Attacks",
RFC 1948, May 1996.
[RFC2018] Mathis, M., Mahdavi, J., Floyd, S. and A. Romanow, "TCP
Selective Acknowledgment Options", RFC 2018, October 1996.
[RFC2385] Heffernan, A., "Protection of BGP Sessions via the TCP MD5
Signature Option", RFC 2385, August 1998.
[RFC2883] Floyd, S., Mahdavi, J., Mathis, M. and M. Podolsky, "An
Extension to the Selective Acknowledgement (SACK) Option
for TCP", RFC 2883, July 2000.
[RFC3042] Allman, M., Balakrishnan, H. and S. Floyd, "Enhancing
TCP's Loss Recovery Using Limited Transmit", RFC 3042,
January 2001.
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[RFC3168] Ramakrishnan, K., Floyd, S. and D. Black, "The Addition of
Explicit Congestion Notification (ECN) to IP", RFC 3168,
September 2001.
[RFC3390] Allman, M., Floyd, S. and C. Partridge, "Increasing TCP's
Initial Window", RFC 3390, October 2002.
[RFC3517] Blanton, E., Allman, M., Fall, K. and L. Wang, "A
Conservative Selective Acknowledgment (SACK)-based Loss
Recovery Algorithm for TCP", RFC 3517, April 2003.
[RFC3562] Leech, M., "Key Management Considerations for the TCP MD5
Signature Option", RFC 3562, July 2003.
[RFC3782] Floyd, S., Henderson, T. and A. Gurtov, "The NewReno
Modification to TCP's Fast Recovery Algorithm", RFC 3782,
April 2004.
9.3 Experimental Extensions
[RFC2140] Touch, J., "TCP Control Block Interdependence", RFC 2140,
April 1997.
[RFC2861] Handley, M., Padhye, J. and S. Floyd, "TCP Congestion
Window Validation", RFC 2861, June 2000.
[RFC3124] Balakrishnan, H. and S. Seshan, "The Congestion Manager",
RFC 3124, June 2001.
[RFC3465] Allman, M., "TCP Congestion Control with Appropriate Byte
Counting (ABC)", RFC 3465, February 2003.
[RFC3522] Ludwig, R. and M. Meyer, "The Eifel Detection Algorithm
for TCP", RFC 3522, April 2003.
[RFC3540] Spring, N., Wetherall, D. and D. Ely, "Robust Explicit
Congestion Notification (ECN) Signaling with Nonces", RFC
3540, June 2003.
[RFC3649] Floyd, S., "HighSpeed TCP for Large Congestion Windows",
RFC 3649, December 2003.
[RFC3708] Blanton, E. and M. Allman, "Using TCP Duplicate Selective
Acknowledgement (DSACKs) and Stream Control Transmission
Protocol (SCTP) Duplicate Transmission Sequence Numbers
(TSNs) to Detect Spurious Retransmissions", RFC 3708,
February 2004.
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[RFC3742] Floyd, S., "Limited Slow-Start for TCP with Large
Congestion Windows", RFC 3742, March 2004.
9.4 Historic Extensions
[RFC1106] Fox, R., "TCP big window and NAK options", RFC 1106, June
1989.
[RFC1110] McKenzie, A., "Problem with the TCP big window option",
RFC 1110, August 1989.
[RFC1146] Zweig, J. and C. Partridge, "TCP alternate checksum
options", RFC 1146, March 1990.
[RFC1263] O'Malley, S. and L. Peterson, "TCP Extensions Considered
Harmful", RFC 1263, October 1991.
[RFC1379] Braden, B., "Extending TCP for Transactions -- Concepts",
RFC 1379, November 1992.
[RFC1644] Braden, B., "T/TCP -- TCP Extensions for Transactions
Functional Specification", RFC 1644, July 1994.
[RFC1693] Connolly, T., Amer, P. and P. Conrad, "An Extension to TCP
: Partial Order Service", RFC 1693, November 1994.
9.5 Support Documents
[RFC0813] Clark, D., "Window and Acknowledgement Strategy in TCP",
RFC 813, July 1982.
[RFC0814] Clark, D., "Name, addresses, ports, and routes", RFC 814,
July 1982.
[RFC0816] Clark, D., "Fault isolation and recovery", RFC 816, July
1982.
[RFC0817] Clark, D., "Modularity and efficiency in protocol
implementation", RFC 817, July 1982.
[RFC0872] Padlipsky, M., "TCP-on-a-LAN", RFC 872, September 1982.
[RFC0879] Postel, J., "TCP maximum segment size and related topics",
RFC 879, November 1983.
[RFC0896] Nagle, J., "Congestion control in IP/TCP internetworks",
RFC 896, January 1984.
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[RFC0964] Sidhu, D. and T. Blumer, "Some problems with the
specification of the Military Standard Transmission
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.
[RFC1072] Jacobson, V. and R. Braden, "TCP extensions for long-delay
paths", RFC 1072, October 1988.
[RFC1156] McCloghrie, K. and M. Rose, "Management Information Base
for network management of TCP/IP-based internets", RFC
1156, May 1990.
[RFC1180] Socolofsky, T. and C. Kale, "TCP/IP tutorial", RFC 1180,
January 1991.
[RFC1185] Jacobson, V., Braden, B. and L. Zhang, "TCP Extension for
High-Speed Paths", RFC 1185, October 1990.
[RFC1213] McCloghrie, K. and M. Rose, "Management Information Base
for Network Management of TCP/IP-based internets:MIB-II",
STD 17, RFC 1213, March 1991.
[RFC1337] Braden, B., "TIME-WAIT Assassination Hazards in TCP", RFC
1337, May 1992.
[RFC1470] Enger, R. and J. Reynolds, "FYI on a Network Management
Tool Catalog: Tools for Monitoring and Debugging TCP/IP
Internets and Interconnected Devices", RFC 1470, June
1993.
[RFC2012] McCloghrie, K., "SNMPv2 Management Information Base for
the Transmission Control Protocol using SMIv2", RFC 2012,
November 1996.
[RFC2398] Parker, S. and C. Schmechel, "Some Testing Tools for TCP
Implementors", RFC 2398, August 1998.
[RFC2415] Poduri, K., "Simulation Studies of Increased Initial TCP
Window Size", RFC 2415, September 1998.
[RFC2416] Shepard, T. and C. Partridge, "When TCP Starts Up With
Four Packets Into Only Three Buffers", RFC 2416, September
1998.
[RFC2452] Daniele, M., "IP Version 6 Management Information Base for
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the Transmission Control Protocol", RFC 2452, December
1998.
[RFC2488] Allman, M., Glover, D. and L. Sanchez, "Enhancing TCP Over
Satellite Channels using Standard Mechanisms", BCP 28, RFC
2488, January 1999.
[RFC2525] Paxson, V., Allman, M., Dawson, S., Fenner, W., Griner,
J., Heavens, I., Lahey, K., Semke, J. and B. Volz, "Known
TCP Implementation Problems", RFC 2525, March 1999.
[RFC2757] Montenegro, G., Dawkins, S., Kojo, M., Magret, V. and N.
Vaidya, "Long Thin Networks", RFC 2757, January 2000.
[RFC2760] Allman, M., Dawkins, S., Glover, D., Griner, J., Tran, D.,
Henderson, T., Heidemann, J., Touch, J., Kruse, H.,
Ostermann, S., Scott, K. and J. Semke, "Ongoing TCP
Research Related to Satellites", RFC 2760, February 2000.
[RFC2884] Hadi Salim, J. and U. Ahmed, "Performance Evaluation of
Explicit Congestion Notification (ECN) in IP Networks",
RFC 2884, July 2000.
[RFC2914] Floyd, S., "Congestion Control Principles", BCP 41, RFC
2914, September 2000.
[RFC2923] Lahey, K., "TCP Problems with Path MTU Discovery", RFC
2923, September 2000.
[RFC3135] Border, J., Kojo, M., Griner, J., Montenegro, G. and Z.
Shelby, "Performance Enhancing Proxies Intended to
Mitigate Link-Related Degradations", RFC 3135, June 2001.
[RFC3360] Floyd, S., "Inappropriate TCP Resets Considered Harmful",
BCP 60, RFC 3360, August 2002.
[RFC3449] Balakrishnan, H., Padmanabhan, V., Fairhurst, G. and M.
Sooriyabandara, "TCP Performance Implications of Network
Path Asymmetry", BCP 69, RFC 3449, December 2002.
[RFC3481] Inamura, H., Montenegro, G., Ludwig, R., Gurtov, A. and F.
Khafizov, "TCP over Second (2.5G) and Third (3G)
Generation Wireless Networks", BCP 71, RFC 3481, February
2003.
[RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J. and W.
Stevens, "Basic Socket Interface Extensions for IPv6", RFC
3493, February 2003.
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[RFC3819] Karn, P., Bormann, C., Fairhurst, G., Grossman, D.,
Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J. and L.
Wood, "Advice for Internet Subnetwork Designers", BCP 89,
RFC 3819, July 2004.
9.6 Informative References Outside the RFC Series
[FACK] Mathis, M. and J. Mahdavi, "Forward Acknowledgement:
Refining TCP Congestion Control", ACM SIGCOMM, August 1996.
[Karn] Karn, P. and C. Partridge, "Round Trip Time Estimation",
ACM SIGCOMM, August 1987.
[Savage] Savage, S., Cardwell, N., Wetherall, D. and T. Anderson,
"TCP Congestion Control with a Misbehaving Receiver", ACM
Computer Communication Review 29 (5), October 1999.
[VJ88] Jacobson, V., "Congestion Avoidance and Control", ACM
SIGCOMM, August 1988.
Authors' Addresses
Martin Duke
Boeing Phantom Works
PO Box 3707, MC 3W-51
Seattle, WA 98124-2207
Phone: 253-657-8203
EMail: mduke26@comcast.net
Robert Braden
USC Information Sciences Institute
Marina del Rey, CA 90292-6695
Phone: 310-448-9173
EMail: braden@isi.edu
Wesley M. Eddy
NASA GRC/Verizon FNS
EMail: weddy@grc.nasa.gov
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Ethan Blanton
Purdue University
EMail: eblanton@cs.purdue.edu
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