draft-ietf-tcpm-experimental-options-01.txt   draft-ietf-tcpm-experimental-options-02.txt 
TCPM Working Group J. Touch TCPM Working Group J. Touch
Internet Draft USC/ISI Internet Draft USC/ISI
Intended status: Proposed Standard May 30, 2012 Intended status: Proposed Standard October 5, 2012
Expires: November 2012 Expires: April 2013
Shared Use of Experimental TCP Options Shared Use of Experimental TCP Options
draft-ietf-tcpm-experimental-options-01.txt draft-ietf-tcpm-experimental-options-02.txt
Status of this Memo Status of this Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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Drafts. Drafts.
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This Internet-Draft will expire on November 30, 2012. This Internet-Draft will expire on April 5, 2013.
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.
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
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publication of this document. Please review these documents publication of this document. Please review these documents
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respect to this document. Code Components extracted from this respect to this document. Code Components extracted from this
document must include Simplified BSD License text as described in document must include Simplified BSD License text as described in
Section 4.e of the Trust Legal Provisions and are provided without Section 4.e of the Trust Legal Provisions and are provided without
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 using a magic number field. This mechanism concurrent experiments using a magic number field. This mechanism
avoids the need for a coordinated registry, and is backward- avoids the need for a coordinated registry, and is backward-
compatible with currently known uses. compatible with currently known uses. It is recommended for all new
experimental RFCs that require TCP option codepoints.
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..............................4
3.1. Reducing the Impact of False Positives....................5 3.1. Reducing the Impact of False Positives....................6
3.2. Migration to Assigned Options.............................6 3.2. Migration to Assigned Options.............................6
4. Security Considerations........................................6 4. Security Considerations........................................7
5. IANA Considerations............................................6 5. IANA Considerations............................................7
6. References.....................................................6 6. References.....................................................7
6.1. Normative References......................................6 6.1. Normative References......................................7
6.2. Informative References....................................7 6.2. Informative References....................................7
7. Acknowledgments................................................7 7. Acknowledgments................................................8
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 30 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 253 and 254 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 codepoints have been used without assignment, notably 31-32 Other codepoints have been used without assignment, notably 31-32
(TCP cookie transactions, as originally distributed and in its API (TCP cookie transactions, as originally distributed and in its API
doc) and 76-78 (tcpcrypt) [Bi11][Si11]. Commercial products doc) and 76-78 (tcpcrypt) [Bi11][Si11]. Commercial products
reportedly also use unassigned options 33 and 76-78 as well. Even reportedly also use unassigned options 33, 69-70, and 76-78 as well.
though these uses are inappropriate, they can impact legitimate Even though these uses are unauthorized, they can impact legitimate
assignees. 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 involvement. The solution involves codepoints and also avoids IANA involvement. The solution involves
adding a field to the structure of the experimental TCP option. This adding a field to the structure of the experimental TCP option. This
field is typically populated with a fixed "magic number" defined as field is typically populated with a fixed "magic number" defined as
part of a specific option experiment. The magic number helps reduce part of a specific option experiment. The magic number helps reduce
the probability of a collision of independent experimental uses of the probability of a collision of independent experimental uses of
the same option codepoint. This feature increases the number of the same option codepoint. This feature increases the number of
bytes used by experimental options, but the size can be reduced when bytes used by experimental options, but the size can be reduced when
the experiment is converted to a standard protocol with a the experiment is converted to a standard protocol with a
conventional codepoint assignment. conventional codepoint assignment.
The solution proposed in this document is recommended for all new
experimental protocols that require TCP option codpoints. This
document also contains suggestions for the transition from this
proposed mechanism to conventionally assigned codepoints, e.g., upon
transition of an experimental protocol to more standards-track use.
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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the Kind and Length, as follows: the Kind and Length, as follows:
+--------+--------+--------+--------+ +--------+--------+--------+--------+
| Kind | Length | Magic Number | | Kind | Length | Magic Number |
+--------+--------+--------+--------+ +--------+--------+--------+--------+
| Magic Number | ... | Magic Number | ...
+--------+--------+--------+--- +--------+--------+--------+---
Figure 2 TCP Experimental Option with a Magic Number Figure 2 TCP Experimental Option with a Magic Number
>> Protocols using the TCP experimental option codepoints (253, 254) >> Protocols defined in experimental RFCs or their precursor
SHOULD use magic numbers as described in this document. Internet Drafts (expecting experimental RFC publication) requiring
new TCP option codepoints SHOULD use the existing TCP experimental
option codepoints (253, 254) with magic numbers as described in this
document.
>> All protocols using the TCP experimental option codepoints (253,
254) SHOULD use magic numbers as described in this document.
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).
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>> 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. This includes the possibility that the magic experimental protocol. This includes the possibility that the magic
number could appear in only a subset of instances of the option. number could appear in only a subset of instances of the option.
Because TCP option capabilities are negotiated during connection Because TCP option capabilities are negotiated during connection
establishment, the magic number might be omitted afterwards (e.g., establishment, the magic number might be omitted afterwards (e.g.,
in non-SYN segments). in non-SYN segments).
>> Experimental option magic numbers, if used, MUST be present in >> TCP experimental option magic numbers, if used in any TCP segment
TCP SYN segments. of a connection, MUST be present in TCP SYN segments of that
connection.
The specification of an experimental option needs to describe The specification of an experimental option needs to describe
whether the magic number appears in non-SYN segments. If the magic whether the magic number appears in non-SYN segments. If the magic
number does not appear in all segments, the experimental option may number does not appear in all segments, the experimental option may
need to be rejected during connection negotiation because options need to be rejected during connection negotiation because options
for different experiments in non-SYN segments may not be for different experiments in non-SYN segments may not be
distinguishable. As a result, this document recommends that: distinguishable. As a result, this document recommends that:
>> Experimental option magic numbers, if used, SHOULD be used in all >> TCP experimental option magic numbers, if used in any TCP segment
TCP segments where the option is present. of a connection, SHOULD be used in all TCP segments of that
connection in which any experimental 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 3.1. Reducing the Impact of False Positives
False positives are always possible, where a magic number matches False positives are always possible, where a magic number matches
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Use of checksums or signatures may help an experiment use a shorter Use of checksums or signatures may help an experiment use a shorter
magic number while reducing the corresponding increased potential magic number while reducing the corresponding increased potential
for false positives. However this document recommends magic numbers for false positives. However this document recommends magic numbers
are used together with such checksums/signatures, not as a are used together with such checksums/signatures, not as a
substitute thereof. Magic numbers are static and thus more easily substitute thereof. Magic numbers are static and thus more easily
identify the experiment using the experimental option; they can also identify the experiment using the experimental option; they can also
be more efficiently interpreted at the TCP receiver. be more efficiently interpreted at the TCP receiver.
3.2. Migration to Assigned Options 3.2. Migration to Assigned Options
This document does not address a specific migration plan to avoid This document does not require a specific migration plan to avoid
the use of magic numbers once an experimental TCP option is the use of magic numbers once a protocol using a experimental TCP
considered for operational deployment, e.g., if it transitions to option codepoint is considered for operational deployment, e.g., if
proposed standard. The expectation is that such options would be it transitions to proposed standard.
assigned their own TCP codepoints and their specifications updated
to avoid the need to support the experimental codepoint. The expectation is that such options would be assigned their own TCP
codepoints and their specifications updated to avoid the need to
support the experimental codepoint. Use of a magic number represents
unnecessary overhead in an assigned TCP codepoint. As a result:
>> Once a specific TCP option codepoint is assigned to a protocol,
that protocol SHOULD NOT continue to use a magic number as part of
that assigned codepoint.
>> The updated protocol specification SHOULD recommend that
implementations intended to be backward-compatible with experimental
deployments MUST support both the experimental codepoint/magic
number and assigned codepoint variants of the option.
Discontinuing support for the experimental codepoint/magic number
variant saves only a small amount of code.
>> Support for the experimental codepoint/magic number variant
SHOULD be discontinued for implementations where the protocol has
been revised in a non-backward-compatible way.
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. security for TCP option processing.
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.
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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-02, (tcpcrypt)", work in progress, draft-bittau-tcp-crypt-03,
Feb. 20, 2012. Sep. 3, 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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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]. Yoshifumi Nishida, Pasi list and by Wes Eddy's proposal [Ed11]. Yoshifumi Nishida, Pasi
Sarolathi, and Michael Sharf provided detailed feedback. Sarolathi, and Michael Scharf 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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