draft-ietf-tcpm-experimental-options-02.txt   draft-ietf-tcpm-experimental-options-03.txt 
TCPM Working Group J. Touch TCPM Working Group J. Touch
Internet Draft USC/ISI Internet Draft USC/ISI
Intended status: Proposed Standard October 5, 2012 Intended status: Proposed Standard November 28, 2012
Expires: April 2013 Expires: May 2013
Shared Use of Experimental TCP Options Shared Use of Experimental TCP Options
draft-ietf-tcpm-experimental-options-02.txt draft-ietf-tcpm-experimental-options-03.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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Abstract Abstract
This document describes how TCP option codepoints can support This document describes how the experimental TCP option codepoints
concurrent experiments using a magic number field. This mechanism can support concurrent use through the use of a magic number. This
avoids the need for a coordinated registry, and is backward- mechanism avoids the need for a coordinated registry and is
compatible with currently known uses. It is recommended for all new backward-compatible with currently known uses. It is recommended for
experimental RFCs that require TCP option codepoints. all new TCP options that use these 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..............................4
3. TCP Experimental Option Structure..............................4 3. TCP Experimental Option Structure..............................4
3.1. Reducing the Impact of False Positives....................6 3.1. Selecting a Magic Number..................................5
3.2. Migration to Assigned Options.............................6 3.2. Impact on TCP Option Processing...........................5
4. Security Considerations........................................7 4. Reducing the Impact of False Positives.........................6
5. IANA Considerations............................................7 5. Migration to Assigned Options..................................7
6. References.....................................................7 6. Security Considerations........................................7
6.1. Normative References......................................7 7. IANA Considerations............................................7
6.2. Informative References....................................7 8. References.....................................................8
7. Acknowledgments................................................8 8.1. Normative References......................................8
8.2. Informative References....................................8
9. Acknowledgments................................................9
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 30 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 values are intended for testing purposes or anytime
implementations need to assume they can be used for other purposes, an assigned codepoint is either not warranted or available, e.g.,
but this is often not the case. based on the maturity status of the defined capability (i.e.,
Experimental or Informational, rather than Standards Track).
There is no mechanism to support shared use of the experimental The term "experimental TCP options" refers here to options that use
option codepoints. Experimental options 253 and 254 are deployed in the experimental TCP option codepoints [RFC4727]. Such experiments
operational code to support an early version of TCP authentication. can be described in any type of RFC - Experimental, Informational,
Option 253 is also documented for the experimental TCP Cookie etc., and are intended to be used both in controlled environments
Transaction option [RFC6013]. This shared use results in collisions and in are allowed in public deployments (when not enabled as
in which a single codepoint can appear multiple times in a single default) [RFC3962]. Nothing prohibits deploying multiple experiments
TCP segment and each use is ambiguous. in the same environment - controlled or public. Further, some
protocols are specified in Experimental or Informational RFCs, which
either include parameters or design choices not yet understood or
which might not be widely deployed [RFC2026]. TCP options in such
RFCs are typically not eligible for assigned TCP option codepoints
[RFC2780], and so there is a need to share use of the experimental
option codepoints.
Other codepoints have been used without assignment, notably 31-32 There is currently no mechanism to support shared use of the
(TCP cookie transactions, as originally distributed and in its API experimental TCP option codepoints. Experimental options 253 and 254
doc) and 76-78 (tcpcrypt) [Bi11][Si11]. Commercial products are already deployed in operational code to support an early version
reportedly also use unassigned options 33, 69-70, and 76-78 as well. of TCP authentication. Option 253 is also documented for the
Even though these uses are unauthorized, they can impact legitimate experimental TCP Cookie Transaction option [RFC6013]. This shared
assignees. use results in collisions in which a single codepoint can appear
multiple times in a single TCP segment and for which each use is
ambiguous.
There are a variety of proposed approaches to address this issue. Other codepoints have been used without assignment (known as
The first is to relax the requirements for assignment of TCP "squatting"), notably 31-32 (TCP cookie transactions, as originally
options, allowing them to be assigned more readily for protocols distributed and in its API doc) and 76-78 (tcpcrypt) [Bi11][Si11].
Commercial products reportedly also use unassigned options 33, 69-
70, and 76-78 as well. Even though these uses are unauthorized, they
currently impact legitimate assignees.
Both such misuses (squatting on both experimental and assigned
codepoints) are expected to continue, but there are several
approaches which can alleviate the impact on cooperating protocol
designers. One proposal relaxes the requirements for assignment of
TCP 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 Another proposal assigns a larger pool to options and manages their
their sharing through IANA coordination [Ed11]. sharing through IANA coordination [Ed11].
This document proposes a solution that does not require additional The approach proposed in this document does not require additional
codepoints and also avoids IANA involvement. The solution involves codepoints and also avoids IANA involvement. The solution adds a
adding a field to the structure of the experimental TCP option. This field to the structure of the experimental TCP option. This field is
field is typically populated with a fixed "magic number" defined as populated with a fixed "magic number" defined as part of a specific
part of a specific option experiment. The magic number helps reduce option experiment. The magic number helps reduce the probability of
the probability of a collision of independent experimental uses of a collision of independent experimental uses of the same option
the same option codepoint. This feature increases the number of codepoint, both for those who follow this document (using other
bytes used by experimental options, but the size can be reduced when magic numbers) and those who do not (squatters).
the experiment is converted to a standard protocol with a
conventional codepoint assignment.
The solution proposed in this document is recommended for all new The solution proposed in this document is recommended for all new
experimental protocols that require TCP option codpoints. This protocols that use experimental TCP option codepoints. The
document also contains suggestions for the transition from this techniques used here may also help share other experimental
proposed mechanism to conventionally assigned codepoints, e.g., upon codepoints, but that issue is out of scope for this document.
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.
In this document, the characters ">>" preceding an indented line(s) In this document, the characters ">>" preceding an indented line(s)
indicates a compliance requirement statement using the key words indicates a compliance requirement statement using the key words
listed above. This convention aids reviewers in quickly identifying listed above. This convention aids reviewers in quickly identifying
or finding the explicit compliance requirements of this RFC. or finding the explicit compliance requirements of this RFC.
3. TCP Experimental Option Structure 3. TCP Experimental Option Structure
TCP options have the current common structure, where the first byte TCP options have the current common structure [RFC793], in which the
is the codepoint (Kind) and the second is the length of the option first byte is the codepoint (Kind) and the second byte is the length
in bytes (Length): of the option in bytes (Length):
0 1 2 3
01234567 89012345 67890123 45678901
+--------+--------+--------+--------+ +--------+--------+--------+--------+
| Kind | Length | ... | | Kind | Length | ... |
+--------+--------+--------+--------+ +--------+--------+--------+--------+
| ... | ...
+-------- +--------
Figure 1 TCP Option Structure [RFC793] Figure 1 TCP Option Structure [RFC793]
This document extends the option structure for experimental This document extends the option structure for experimental
codepoints (253, 254) with a magic number. The magic number is used codepoints (253, 254) with a magic number, which is typically 4
to differentiate different experiments, and is the first field after bytes in length. The magic number is used to differentiate different
the Kind and Length, as follows: experiments, and is the first field after the Kind and Length, as
follows:
0 1 2 3
01234567 89012345 67890123 45678901
+--------+--------+--------+--------+ +--------+--------+--------+--------+
| 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 defined in experimental RFCs or their precursor >> Protocols requiring new TCP option codepoints that are not
Internet Drafts (expecting experimental RFC publication) requiring eligible for assigned values SHOULD use the existing TCP
new TCP option codepoints SHOULD use the existing TCP experimental experimental option codepoints (253, 254) with magic numbers as
option codepoints (253, 254) with magic numbers as described in this described in this document.
document.
>> All protocols using the TCP experimental option codepoints (253, >> All protocols using the TCP experimental option codepoints (253,
254) SHOULD use magic numbers as described in this document. 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]. In the use proposed in this document they help
that share the same TCP option codepoint do not interfere. ensure that concurrent experiments that share the same TCP option
codepoint do not interfere.
3.1. Selecting a Magic Number
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, i.e., when the specification for
a variety of ways, e.g., using the Unix time() command or bits that option is authored. The magic number is selected any of a
selected by an arbitrary function (such as a hash). variety of ways, e.g., using the Unix time() command or bits
selected by an arbitrary function (such as a hash) of an arbitrary
string (e.g., the document title). This operation occurs only when
the option is specified, and is not implemented as part of the
design of an option.
This document does not proscribe a minimum magic number size. Larger
magic numbers reduce the probability of a collision with other
options sharing the Kind codepoint, but also increase the option
size. A suggested size is 32 bits, in network standard byte order:
>> The magic number size and 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.
This document does not proscribe a minimum magic number size.
However, a reasonable suggested size is 32 bits, in network standard
byte order:
>> The magic number SHOULD be 32 bits, but MAY be either longer or >> The magic number SHOULD be 32 bits, but MAY be either longer or
shorter. shorter.
3.2. Impact on TCP Option Processing
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.
skipping to change at page 6, line 5 skipping to change at page 6, line 36
>> TCP experimental option magic numbers, if used in any TCP segment >> TCP experimental option magic numbers, if used in any TCP segment
of a connection, SHOULD be used in all TCP segments of that of a connection, SHOULD be used in all TCP segments of that
connection in which any experimental option is present. 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 4. Reducing the Impact of False Positives
False positives are always possible, where a magic number matches False positives occur where the magic number of one experiment
the value of a field in the legacy use of these options or a matches the value of an option that does not use magic numbers or if
protocol that does not implement the mechanism described in this two experiments select the same magic number. Such collisions can
document. cause an option to be interpreted by the incorrect processing
routine.
>> Protocols that are not robust to magic number false positives >> Experiments that are not robust to magic number false positives
SHOULD implement other measures to ensure they process options for SHOULD implement other detection measures, such as checksums or
their protocol only, such as checksums or digital signatures among digital signatures.
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 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 5. Migration to Assigned Options
This document does not require a specific migration plan to avoid Some experiments may transition from experiment, and become eligible
the use of magic numbers once a protocol using a experimental TCP for an assigned TCP option codepoint. This document does not
option codepoint is considered for operational deployment, e.g., if recommend a specific migration plan to transition from use of the
it transitions to proposed standard. experimental TCP options/magic numbers to use of an assigned
codepoint.
The expectation is that such options would be assigned their own TCP However, once an assigned codepoint is allocated, use of a magic
codepoints and their specifications updated to avoid the need to number represents unnecessary overhead. As a result:
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, >> Once a TCP option codepoint is assigned to a protocol, that
that protocol SHOULD NOT continue to use a magic number as part of protocol SHOULD NOT continue to use a magic number as part of that
that assigned codepoint. assigned codepoint.
>> The updated protocol specification SHOULD recommend that This document does not recommend whether or how an implementation of
implementations intended to be backward-compatible with experimental an assigned codepoint should be backward-compatible with use of the
deployments MUST support both the experimental codepoint/magic experimental codepoint/magic number.
number and assigned codepoint variants of the option.
Discontinuing support for the experimental codepoint/magic number However, some implementers may be tempted to include both the
variant saves only a small amount of code. experimental and assigned codepoint in the same segment, e.g., in a
SYN to support backward-compatibility during connection
establishment. This is a poor use limited resources and so to ensure
conservation of the TCP option space:
>> Support for the experimental codepoint/magic number variant >> A TCP segment MUST NOT contain both an assigned TCP option
SHOULD be discontinued for implementations where the protocol has codepoint and an experimental TCP option codepoint/magic number for
been revised in a non-backward-compatible way. the same protocol.
4. Security Considerations Instead, a TCP that intends backward compatibility might send
multiple SYNs with alternates of the same option and discard all but
the most desired successful connection.
6. 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. (nor does it weaken existing) security for TCP option processing.
5. IANA Considerations 7. 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 8. References
6.1. Normative References 8.1. Normative References
[RFC793] Postel, J., "Transmission Control Protocol", STD 7, RFC [RFC793] Postel, J., "Transmission Control Protocol", STD 7, RFC
793, Sep. 1981. 793, Sep. 1981.
[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 8.2. 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-03, (tcpcrypt)", work in progress, draft-bittau-tcp-crypt-03,
Sep. 3, 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.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, Oct. 1996.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, Mar. 1997. 2131, Mar. 1997.
[RFC2780] Bradner, S., V. Paxson, "IANA Allocation Guidelines For
Values In the Internet Protocol and Related Headers", BCP
37, RFC 2780, Mar. 2000.
[RFC3962] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3962, Jan. 2004.
[RFC5226] Narten, T., H. Alvestrand, "Guidelines for Writing an IANA [RFC5226] Narten, T., H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 5226, May Considerations Section in RFCs", BCP 26, RFC 5226, May
2008. 2008.
[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 9. 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 Scharf 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
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