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Network Working Group                                            W. Eddy
Internet-Draft                                               MTI Systems
Updates: 4727 (if approved)                              August 16, 2011
Intended status: Standards Track
Expires: February 17, 2012

                Additional TCP Experimental-Use Options


   There have been multiple issues with the allocation of TCP option
   kind numbers recently.  Two of these issues, which this document
   attempts to address, are that there were only a small number of
   options reserved by RFC 4727 for experiment and test use in the RFC
   3692 style to begin with, and both of these have been used in
   shipping products.  This impacts the ability of other research and
   experimental efforts to develop and test running code since
   registration of other option numbers requires either IESG Approval or
   Standards Action.  This document proposes designation of additional
   experimental options in the IANA registry for TCP Option Kind
   Numbers, intended to resolve the possible barriers to using the
   existing RFC 3962 experimental-use options.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.  This document may not be modified,
   and derivative works of it may not be created, except to format it
   for publication as an RFC and to translate it into languages other
   than English.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on February 17, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the

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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Additional Experimental-Use Options . . . . . . . . . . . . . . 4
   3.  Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     6.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     6.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 6

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1.  Introduction

   TCP options are a fundamental mechanism for extending and enhancing
   TCP's functionality.  In the past, the addition of TCP options (e.g.
   Window Scale, Timestamp [RFC1323], and Selective Acknowledgements
   [RFC2018]) has supported the protocol's evolution and helped its
   applicability to expand as the Internet and types of links available

   However, there has been significant confusion with regards to how TCP
   option kind numbers are managed.  This is, frankly, dangerous to the
   Internet, if it persists.  There is a limited pool of options and due
   to misunderstandings the usable portion of this pool has shrunk to an
   unknown extent.

   Registration of TCP option kind numbers is a function of the IANA
   [RFC2780].  Values are assigned following either (1) IESG Approval,
   or (2) Standards Action process, which are defined in [RFC2434].
   Some vendors have not followed these procedures and simply shipped
   products using option kind numbers chosen themselves.  This poisons
   the pool of options available, as it potentially causes conflicts if
   IANA later registers those same kind numbers for a use that followed
   the proper registration process.  This has been recognized as a
   mistake, and vendors have expressed a desire to avoid it in the
   future and are working towards possible transition of such products
   to registered options numbers.

   Two TCP option numbers have been designated for experimental use
   [RFC4727], which are not intended to be used in general deployments
   or enabled by default in products or other general releases unless
   explicitly enabled by an end-user [RFC3692].

   Unfortunately, at least one vendor intending to avoid shipping its
   products using unregistered option numbers, actually shipped products
   using the experimental-use numbers.  These numbers are being used by
   some deployed middleboxes and the impacts to other people trying to
   use the same kind numbers for other purposes is not broadly
   understood, especially since the presence of such middleboxes on a
   path may be unknown a priori.

   A recent TCP research effort testing running code over the Internet
   that would have been a perfect candidate for using the experimental-
   use numbers shied away from this due to the deployed middlebox issue
   and chose to improperly use yet more unregistered TCP option kind

   Another recent issue is that with multiple ongoing efforts to extend
   TCP, there may be implementations that integrate a number of

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   extensions requiring experimental-use options.  Two kind numbers may
   not be sufficient for such cases, and adding sub-kind identifiers
   within the option payload may be complex or even impossible.

   This document attempts to mitigate the situation and remove excuses
   for such instances in the future by requesting IANA to register a
   greater number of TCP experimental-use options that would also follow
   the RFC 3692 spirit for their intended use.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119.  [RFC2119]

2.  Additional Experimental-Use Options

   This document proposes to create an additional sixteen experimental-
   use TCP option kinds in the spirit of RFC 3692.  As this may seem
   like a large number compared to the current two that RFC 4727
   requested, some rationale is provided in the next section.

   Of these sixteen option kinds, the option-length field for all of
   them will be defined as variable, but in all cases will hold a value
   of at least 2 in order to account for the kind and length fields.

   The option kind numbers allocated should be contiguous in order to
   support potential ease of updating filter rules and other databases
   used in firewalls and other middleboxes, as well as various other
   software tools for packet analysis and other uses.

3.  Rationale

   There are only 8 bits that comprise a TCP Option Kind field, lending
   256 possible unique codepoints.  Of these, there are the 2 identified
   in RFC 4727 for experimental-use and 19 with registrations that are
   currently not identified as obsolete (historic and currently unused)
   or unassigned due to release of prior registrations.  Of these,
   several are not known to be in general use and could likely be reaped
   if needed.  Additionally, 11 kind numbers have been identified as
   obsolete or unassigned due to registration being released, and 6 more
   are known to be deployed without proper IANA assignment.  One further
   protocol under development in the IETF (Multipath TCP) requires an
   IANA option kind assignment yet-to-be-made.

   This leaves 217 option kind values that both have never been
   registered and are not known to have been under deployment without
   registration.  Even though this document proposes to claim 16 of

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   these values for experimental-use, there will still be 201 option
   kind values seemingly fully available, which represents over 78% of
   the option kind numbers.  Based on TCP's existence for several
   decades without even using a quarter of the available options space,
   the remaining pool of kind numbers should be sufficient for many more
   decades to come.

   Further, 16 option numbers for experimental use should be more than
   sufficient by a factor of 2 to 4 in order to permit implementing and
   testing combinations of experimental TCP extensions that do not yet
   have their own registered option kind numbers.  This is especially
   true as recently Multipath TCP design has set an example for using a
   sub-kind / subtype field in order to avoid requiring multiple kind
   numbers from the TCP registry.  This practice could be reused by
   future similar extensions making extensive use of TCP options.

4.  Security Considerations

   This document creates no additional security considerations for TCP

   Firewalls and other network devices that aggressively filter
   unrecognized TCP options may cause difficulties in using the new
   experimental-use kind numbers defined by this document.  Managers and
   vendors of such firewalls should reconsider whether such filtering is
   necessary or useful as this practice represents a major impediment to
   innovation in TCP.

5.  IANA Considerations

   This document requests that IANA allocate sixteen contiguous TCP
   option values for experimental-use in the spirit of RFC 3692, which
   will be described in the registry as:

   o  Length: N

   o  Meaning: RFC3692-style Experiment - MUST NOT be used by default in
      shipping products, or other uncontrolled wide-scale deployments
      outside of an experimental context

   o  Reference: (this document's RFC number, to be filled in)

   Allocation from the rear of the available reserved space adjacent
   below the two existing experimental-use options (253 and 254) is

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6.  References

6.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4727]  Fenner, B., "Experimental Values In IPv4, IPv6, ICMPv4,
              ICMPv6, UDP, and TCP Headers", RFC 4727, November 2006.

6.2.  Informative References

   [RFC1323]  Jacobson, V., Braden, B., and D. Borman, "TCP Extensions
              for High Performance", RFC 1323, May 1992.

   [RFC2018]  Mathis, M., Mahdavi, J., Floyd, S., and A. Romanow, "TCP
              Selective Acknowledgment Options", RFC 2018, October 1996.

   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 2434,
              October 1998.

   [RFC2780]  Bradner, S. and V. Paxson, "IANA Allocation Guidelines For
              Values In the Internet Protocol and Related Headers",
              BCP 37, RFC 2780, March 2000.

   [RFC3692]  Narten, T., "Assigning Experimental and Testing Numbers
              Considered Useful", BCP 82, RFC 3692, January 2004.

Author's Address

   Wesley M. Eddy
   MTI Systems
   MS 500-ASRC
   NASA Glenn Research Center
   21000 Brookpark Road
   Cleveland, OH  44135

   Phone: +1-216-433-6682
   Email: wes@mti-systems.com

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