draft-ietf-tcpm-experimental-options-00.txt   draft-ietf-tcpm-experimental-options-01.txt 
TCPM Working Group J. Touch TCPM Working Group J. Touch
Internet Draft USC/ISI Internet Draft USC/ISI
Intended status: Proposed Standard January 17, 2012 Intended status: Proposed Standard May 30, 2012
Expires: July 2012 Expires: November 2012
Shared Use of Experimental TCP Options Shared Use of Experimental TCP Options
draft-ietf-tcpm-experimental-options-00.txt draft-ietf-tcpm-experimental-options-01.txt
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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warranty as described in the Simplified BSD License. warranty as described in the Simplified BSD License.
Abstract Abstract
This document describes how TCP option codepoints can support This document describes how TCP option codepoints can support
concurrent experiments. The suggested mechanism avoids the need for concurrent experiments using a magic number field. This mechanism
a coordinated registry, and is backward-compatible with currently avoids the need for a coordinated registry, and is backward-
known uses. compatible with currently known uses.
Table of Contents Table of Contents
1. Introduction...................................................2 1. Introduction...................................................2
2. Conventions used in this document..............................3 2. Conventions used in this document..............................3
3. TCP Experimental Option Structure..............................3 3. TCP Experimental Option Structure..............................3
4. Security Considerations........................................5 3.1. Reducing the Impact of False Positives....................5
5. IANA Considerations............................................5 3.2. Migration to Assigned Options.............................6
6. References.....................................................5 4. Security Considerations........................................6
6.1. Normative References......................................5 5. IANA Considerations............................................6
6.2. Informative References....................................6 6. References.....................................................6
7. Acknowledgments................................................6 6.1. Normative References......................................6
6.2. Informative References....................................7
7. Acknowledgments................................................7
1. Introduction 1. Introduction
TCP includes options to enable new protocol capabilities that can be TCP includes options to enable new protocol capabilities that can be
activated only where needed and supported [RFC793]. The space for activated only where needed and supported [RFC793]. The space for
identifying such options is small - 256 values, of which 31 are identifying such options is small - 256 values, of which 31 are
assigned at the time this document was published [IANA]. Two of assigned at the time this document was published [IANA]. Two of
these codepoints are allocated to support experiments (253, 254) these codepoints are allocated to support experiments (253, 254)
[RFC4727]. These numbers are intended for testing purposes, and [RFC4727]. These numbers are intended for testing purposes, and
implementations need to assume they can be used for other purposes, implementations need to assume they can be used for other purposes,
but this is often not the case. but this is often not the case.
There is no mechanism to support shared use of the experimental There is no mechanism to support shared use of the experimental
option codepoints. Experimental options 245 and 255 are deployed in option codepoints. Experimental options 253 and 254 are deployed in
operational code to support an early version of TCP authentication. operational code to support an early version of TCP authentication.
Option 253 is also documented for the experimental TCP Cookie Option 253 is also documented for the experimental TCP Cookie
Transaction option [RFC6013]. This shared use results in collisions Transaction option [RFC6013]. This shared use results in collisions
in which a single codepoint can appear multiple times in a single in which a single codepoint can appear multiple times in a single
TCP segment and each use is ambiguous. TCP segment and each use is ambiguous.
Other options have been used without assignment, notably 31-32 (TCP Other codepoints have been used without assignment, notably 31-32
cookie transactions, as originally distributed and in its API doc) (TCP cookie transactions, as originally distributed and in its API
and 76-78 (tcpcrypt) [Bi11][Si11]. Commercial products reportedly doc) and 76-78 (tcpcrypt) [Bi11][Si11]. Commercial products
also use unassigned options 33 and 76-78 as well. reportedly also use unassigned options 33 and 76-78 as well. Even
though these uses are inappropriate, they can impact legitimate
assignees.
There are a variety of proposed approaches to address this issue. There are a variety of proposed approaches to address this issue.
The first is to relax the requirements for assignment of TCP The first is to relax the requirements for assignment of TCP
options, allowing them to be assigned more readily for protocols options, allowing them to be assigned more readily for protocols
that have not been standardized through the IETF process [RFC5226]. that have not been standardized through the IETF process [RFC5226].
A second would be to assign a larger pool to options, and to manage A second would be to assign a larger pool to options, and to manage
their sharing through IANA coordination [Ed11]. their sharing through IANA coordination [Ed11].
This document proposes a solution that does not require additional This document proposes a solution that does not require additional
codepoints and also avoids IANA participation. A short magic number codepoints and also avoids IANA involvement. The solution involves
is added to the structure of the experimental TCP option structure. adding a field to the structure of the experimental TCP option. This
The magic number helps reduce the probability of collision of field is typically populated with a fixed "magic number" defined as
independent experimental uses of the same option codepoint. This part of a specific option experiment. The magic number helps reduce
feature increases the size of experimental options, but the size can the probability of a collision of independent experimental uses of
be reduced when the experiment is converted to a standard protocol the same option codepoint. This feature increases the number of
with a conventional codepoint assignment. bytes used by experimental options, but the size can be reduced when
the experiment is converted to a standard protocol with a
conventional codepoint assignment.
2. Conventions used in this document 2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [RFC2119]. document are to be interpreted as described in RFC-2119 [RFC2119].
In this document, these words will appear with that interpretation In this document, these words will appear with that interpretation
only when in ALL CAPS. Lower case uses of these words are not to be only when in ALL CAPS. Lower case uses of these words are not to be
interpreted as carrying RFC-2119 significance. interpreted as carrying RFC-2119 significance.
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Magic numbers are used in other protocols, e.g., BOOTP [RFC951] and Magic numbers are used in other protocols, e.g., BOOTP [RFC951] and
DHCP [RFC2131]. Here they help ensure that concurrent experiments DHCP [RFC2131]. Here they help ensure that concurrent experiments
that share the same TCP option codepoint do not interfere. that share the same TCP option codepoint do not interfere.
The magic number is selected by the protocol designer when an The magic number is selected by the protocol designer when an
experimental option is defined. The magic number is selected any of experimental option is defined. The magic number is selected any of
a variety of ways, e.g., using the Unix time() command or bits a variety of ways, e.g., using the Unix time() command or bits
selected by an arbitrary function (such as a hash). selected by an arbitrary function (such as a hash).
>> The magic number value SHOULD be selected to reduce the >> The magic number size and value SHOULD be selected to reduce the
probability of collision. probability of collision.
The length of the magic number is a 32 bit value in network standard This document does not proscribe a minimum magic number size.
byte order. It can be shorter if desired (e.g., 16 bits), with a However, a reasonable suggested size is 32 bits, in network standard
corresponding increased probability of collision and thus false byte order:
positives.
>> The magic number SHOULD be 32 bits long; it MAY be as few as 16 >> The magic number SHOULD be 32 bits, but MAY be either longer or
bits if desired. shorter.
The magic number is considered part of the TCP option, not the TCP The magic number is considered part of the TCP option, not the TCP
option header. The presence of the magic number increases the option header. The presence of the magic number increases the
effective option Length field by the size of the magic number. The effective option Length field by the size of the magic number. The
presence of this magic number is thus transparent to implementations presence of this magic number is thus transparent to implementations
that do not support TCP options where it is used. that do not support TCP options where it is used.
During TCP processing, experimental options are matched against both During TCP processing, experimental options are matched against both
the experimental codepoints and the magic number value for each the experimental codepoints and the magic number value for each
implemented protocol. implemented protocol.
>> Experimental options that have magic numbers that do not match >> Experimental options that have magic numbers that do not match
implemented protocols MUST be ignored. implemented protocols MUST be ignored.
The remainder of the option is specified by the particular The remainder of the option is specified by the particular
experimental protocol. experimental protocol. This includes the possibility that the magic
number could appear in only a subset of instances of the option.
Because TCP option capabilities are negotiated during connection
establishment, the magic number might be omitted afterwards (e.g.,
in non-SYN segments).
>> Experimental option magic numbers, if used, MUST be present in
TCP SYN segments.
The specification of an experimental option needs to describe
whether the magic number appears in non-SYN segments. If the magic
number does not appear in all segments, the experimental option may
need to be rejected during connection negotiation because options
for different experiments in non-SYN segments may not be
distinguishable. As a result, this document recommends that:
>> Experimental option magic numbers, if used, SHOULD be used in all
TCP segments where the option is present.
Use of a magic number uses additional space in the TCP header and Use of a magic number uses additional space in the TCP header and
requires additional protocol processing by experimental protocols. requires additional protocol processing by experimental protocols.
Because these are experiments, neither consideration is a Because these are experiments, neither consideration is a
substantial impediment; a finalized protocol can avoid both issues substantial impediment; a finalized protocol can avoid both issues
with the assignment of a dedicated option codepoint later. with the assignment of a dedicated option codepoint later.
3.1. Reducing the Impact of False Positives
False positives are always possible, where a magic number matches
the value of a field in the legacy use of these options or a
protocol that does not implement the mechanism described in this
document.
>> Protocols that are not robust to magic number false positives
SHOULD implement other measures to ensure they process options for
their protocol only, such as checksums or digital signatures among
cooperating parties of their protocol. Such measures SHOULD
supplement, rather than substitute for, the use of magic numbers.
Use of checksums or signatures may help an experiment use a shorter
magic number while reducing the corresponding increased potential
for false positives. However this document recommends magic numbers
are used together with such checksums/signatures, not as a
substitute thereof. Magic numbers are static and thus more easily
identify the experiment using the experimental option; they can also
be more efficiently interpreted at the TCP receiver.
3.2. Migration to Assigned Options
This document does not address a specific migration plan to avoid This document does not address a specific migration plan to avoid
the use of magic numbers once an experimental TCP option is the use of magic numbers once an experimental TCP option is
considered for operational deployment, e.g., if it transitions to considered for operational deployment, e.g., if it transitions to
proposed standard. The expectation is that such options would be proposed standard. The expectation is that such options would be
assigned their own TCP codepoints and their specifications updated assigned their own TCP codepoints and their specifications updated
to avoid the need to support the experimental codepoint to avoid the need to support the experimental codepoint.
4. Security Considerations 4. Security Considerations
The mechanism described in this document is not intended to provide The mechanism described in this document is not intended to provide
security for TCP option processing. False positives are always security for TCP option processing.
possible, where a magic number matches the value of a field in the
legacy use of these options or a protocol that does not implement
the mechanism described in this document.
>> Protocols that are not robust to such false positives SHOULD
implement other measures to ensure they process options for their
protocol only, such as checksums or digital signatures among
cooperating parties of their protocol.
5. IANA Considerations 5. IANA Considerations
This document has no IANA considerations. This section should be This document has no IANA considerations. This section should be
removed prior to publication. removed prior to publication.
6. References 6. References
6.1. Normative References 6.1. Normative References
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4727] Fenner, B., "Experimental Values in IPv4, IPv6, ICMPv4, [RFC4727] Fenner, B., "Experimental Values in IPv4, IPv6, ICMPv4,
ICMPv6, UDP, and TCP Headers", RFC 4727, Nov. 2006. ICMPv6, UDP, and TCP Headers", RFC 4727, Nov. 2006.
6.2. Informative References 6.2. Informative References
[Bi11] Bittau, A., D. Boneh, M. Hamburg, M. Handley, D. Mazieres, [Bi11] Bittau, A., D. Boneh, M. Hamburg, M. Handley, D. Mazieres,
Q. Slack, "Cryptographic protection of TCP Streams Q. Slack, "Cryptographic protection of TCP Streams
(tcpcrypt)", work in progress, draft-bittau-tcp-crypt-01, (tcpcrypt)", work in progress, draft-bittau-tcp-crypt-02,
Aug. 29, 2011. Feb. 20, 2012.
[Ed11] Eddy, W., "Additional TCP Experimental-Use Options", work [Ed11] Eddy, W., "Additional TCP Experimental-Use Options", work
in progress, draft-eddy-tcpm-addl-exp-options-00, Aug. 16, in progress, draft-eddy-tcpm-addl-exp-options-00, Aug. 16,
2011. 2011.
[IANA] IANA web pages, http://www.iana.org/ [IANA] IANA web pages, http://www.iana.org/
[RFC951] Croft, B., J. Gilmore, "BOOTSTRAP PROTOCOL (BOOTP)", RFC [RFC951] Croft, B., J. Gilmore, "BOOTSTRAP PROTOCOL (BOOTP)", RFC
951, Sept. 1985. 951, Sept. 1985.
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[RFC6013] Simpson, W., "TCP Cookie Transactions (TCPCT)", RFC 6013, [RFC6013] Simpson, W., "TCP Cookie Transactions (TCPCT)", RFC 6013,
Jan. 2011. Jan. 2011.
[Si11] Simpson, W., "TCP Cookie Transactions (TCPCT) Sockets [Si11] Simpson, W., "TCP Cookie Transactions (TCPCT) Sockets
Application Program Interface (API)", work in progress, Application Program Interface (API)", work in progress,
draft-simpson-tcpct-api-04, Apr. 7, 2011. draft-simpson-tcpct-api-04, Apr. 7, 2011.
7. Acknowledgments 7. Acknowledgments
This document was motivated by discussions on the IETF TCPM mailing This document was motivated by discussions on the IETF TCPM mailing
list and by Wes Eddy's proposal [Ed11]. list and by Wes Eddy's proposal [Ed11]. Yoshifumi Nishida, Pasi
Sarolathi, and Michael Sharf provided detailed feedback.
This document was prepared using 2-Word-v2.0.template.dot. This document was prepared using 2-Word-v2.0.template.dot.
Authors' Addresses Authors' Addresses
Joe Touch Joe Touch
USC/ISI USC/ISI
4676 Admiralty Way 4676 Admiralty Way
Marina del Rey, CA 90292-6695 U.S.A. Marina del Rey, CA 90292-6695 U.S.A.
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