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TCP Maintenance and Minor Extensions (tcpm)                A. Zimmermann
Internet-Draft                                          R. Scheffenegger
Intended status: Standards Track                            NetApp, Inc.
Expires: January 1, 2016                                      B. Briscoe

                                                           June 30, 2015


                The TCP Echo and TCP Echo Reply Options
                  draft-zimmermann-tcpm-echo-option-00

Abstract

   This document specifies the TCP Echo and TCP Echo Reply options.  It
   provides a single field a TCP sender can use to store any type of
   data that a TCP receiver simply echo unmodified back.  In contrast to
   the original TCP Echo and TCP Echo Reply options defined in RFC 1072
   the options specified in this document have slightly different
   semantics and support a variable option length.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   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 January 1, 2016.

Copyright Notice

   Copyright (c) 2015 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   to this document.  Code Components extracted from this document must



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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.

1.  Introduction

   This document specifies the TCP Echo and TCP Echo Reply options.  It
   provides a single field a TCP sender can use to store any type of
   data that a TCP receiver simply echo unmodified back.  In contrast to
   the original TCP Echo and TCP Echo Reply options defined in RFC 1072
   [RFC1072] the options specified in this document have a slightly
   different semantics and support a variable option length.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].  These
   words only have such normative significance when in ALL CAPS, not
   when in lower case.

3.  The TCP Echo and TCP Echo Reply options

   The general structure of TCP options is defined in [RFC0793].  The
   TCP Echo option is organized as indicated in Figure 1.

           0                   1                   2
           0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 ...
           +---------------+---------------+-------- ... ------+
           |    Kind A     |    Length     |    Data           |
           +---------------+---------------+-------- ... ------+

                       Figure 1: The TCP Echo option

   The codepoint value of the TCP Echo 'Kind A' is {ToDo: Value TBA}.
   The value of the 'Length' field in octets can be any value greater
   than 1 as long as the TCP Echo option completely fits into TCP option
   space, which may be extended (see [RFC0793], [I-D.ietf-tcpm-tcp-edo],
   [I-D.briscoe-tcpm-inner-space]).  The optional 'Data' field is
   available for the TCP sender to fill with any amount of any type of
   data it wishes to be send back by the TCP receiver in a subsequent
   TCP Echo Reply option (see Figure 2).  It is only be constrained in
   size to an integer number of octets.

   The TCP Echo facility is determined in both directions using a single
   exchange during the 3-way handshake [RFC0793].  A TCP seeking to use
   TCP Echo facility includes the TCP Echo option in the initial SYN or
   SYN/ACK.  If the TCP receiver of that SYN or SYN/ACK agrees to



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   support TCP Echo facility, it MUST respond with TCP Echo Reply option
   (see Figure 2) in its corresponding segment.

   Both TCP endpoints MAY use the TCP Echo facility in any segment, but
   only if the TCP Echo option was received in a segment with the SYN
   bit set (i.e., SYN and SYN/ACK) or the TCP Echo Reply option was
   received in response to a sent TCP Echo option.  In all cases an
   endpoint MUST NOT include more than one TCP Echo option per segment.

   A TCP sender MAY send an empty TCP Echo option with Length=2 on the
   SYN, to only indicate that it supports the TCP Echo facility.  In
   that case, the TCP receiver of that SYN MUST response with and empty
   TCP Echo Reply option with Length=2 accordingly.

   The TCP Echo Reply option is organized as indicated in Figure 2.

           0                   1                   2
           0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 ...
           +---------------+---------------+-------- ... ------+
           |    Kind B     |    Length     |    Data           |
           +---------------+---------------+-------- ... ------+

                    Figure 2: The TCP Echo Reply Option

   A TCP receiver that does not implement the TCP Echo facility or
   decides to not use the TCP Echo facility for this particular
   connection MUST silently ignore any TCP Echo options it receives for
   this connection.  If the TCP receiver has reflected the TCP Echo
   option in its SYN/ACK during the 3-way handshake, it MUST reply to
   any TCP Echo option received during this connection.

   Once enabled on a connection, a TCP receiver that receives a TCP Echo
   option MUST return the same bytes of the Data field in a TCP Echo
   Reply option.  This TCP Echo Reply option MUST returned in the next
   segment (e.g., an ACK segment) that is sent.  If due to the delayed
   ACK algorithm [RFC1122] more than one TCP Echo option is received
   before a reply segment is sent, the TCP receiver MUST choose only one
   of the options to echo, ignoring the others; specifically, it MUST
   choose the most recently received TCP Echo option to echo back (i.e.
   Last In, First Out - LIFO).

4.  IANA Considerations

   This specification requires IANA to allocate a value from the TCP
   option kind name-space against the name

      'Kind A'
      'Kind B'



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   Early implementation before the IANA allocation MUST follow [RFC6994]
   and use experimental option 254 and respective Experiment ID:

      0xEC01 (16 bits) for the TCP Echo option;
      0xEC02 (16 bits) for the TCP Echo Reply option;

   The Echo option defined in RFC1072 [RFC1072] specifies different
   semantics, which do not lend themselves for reuse.  Specifically,
   RFC1072 [RFC1072] specifies to select the TCP Echo option data from
   the newest segment with the oldest sequence number, while herein we
   specify to return the TCP Echo option of the most recently received
   segment, regardless of sequence numbers.

   {ToDo: Values TBA and register them with IANA} then migrate to the
   assigned option after allocation.}

5.  Security Considerations

   An implementation should not rely on this facility for critical TCP
   mechanisms, before ensuring that the TCP Echo option data field is
   reflected back properly and unmodified.  If the TCP Echo option is
   considered critical, a TCP mechanism should have means to verify the
   integrity of the data contained in the TCP Echo Reply option.
   Additionally, a malicious receiver or network device may infer the
   utility of the data in a TCP Echo option, and interpret it for its
   purposes.  A designer using the TCP Echo facility needs to consider
   this, and take appropriate measures to prevent misuse of the data
   sent.

   Since TCP options are not delivered reliably, a TCP Echo or TCP Echo
   Reply option may be lost or reordered at any time, a TCP mechanisms
   MUST to deal appropriately with this occurrences.

   If multiple TCP mechanisms want to make use of the TCP Echo facility,
   the implementer should accommodate for that, for example by encoding
   the multiple inputs accordingly into the data field of the TCP Echo
   option.

   Some middleboxes have been known to remove TCP options unknown to
   them like those described in this document (see [Honda11]).  As the
   TCP Echo and TCP Echo Reply option use two different option numbers,
   it is conceivable that only one or the other may get stripped from a
   segment, in one direction, resulting in an unidirectional usability
   of the TCP Echo facility.







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6.  Privacy Considerations

   This document describes a new mechanism to tag individual TCP
   segments.  However, the TCP options described do not expose
   individual user's data.  In order to better maintain the
   confidentiality of data exchanged on the wire, and to address some
   aspects of security, it is NOT RECOMMENDED to send easily
   decipherable data in the clear as data in the TCP Echo option.

7.  Acknowledgements

   Alexander Zimmermann have received funding from the European Union's
   Horizon 2020 research and innovation program 2014-2018 under grant
   agreement No. 644866 (SSICLOPS).  This document reflects only the
   authors' views and the European Commission is not responsible for any
   use that may be made of the information it contains.

8.  References

8.1.  Normative References

   [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.

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

   [RFC6994]  Touch, J., "Shared Use of Experimental TCP Options", RFC
              6994, August 2013.

8.2.  Informative References

   [Honda11]  Honda, M., Nishida, Y., Raiciu, C., Greenhalgh, A.,
              Handley, M., and H. Tokuda, "Is it still possible to
              extend TCP?", Proc. of ACM Internet Measurement Conference
              (IMC) '11, November 2011.

   [I-D.briscoe-tcpm-inner-space]
              Briscoe, B., "Inner Space for TCP Options", draft-briscoe-
              tcpm-inner-space-01 (work in progress), October 2014.

   [I-D.ietf-tcpm-tcp-edo]
              Touch, J. and W. Eddy, "TCP Extended Data Offset Option",
              draft-ietf-tcpm-tcp-edo-01 (work in progress), October
              2014.



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   [RFC1072]  Jacobson, V. and R. Braden, "TCP extensions for long-delay
              paths", RFC 1072, October 1988.

Authors' Addresses

   Alexander Zimmermann
   NetApp, Inc.
   Sonnenallee 1
   Kirchheim  85551
   Germany

   Phone: +49 89 900594712
   Email: alexander.zimmermann@netapp.com


   Richard Scheffenegger
   NetApp, Inc.
   Am Euro Platz 2
   Vienna  1120
   Austria

   Email: rs@netapp.com


   Bob Briscoe

   Email: ietf@bobbriscoe.net
   URI:   http://bobbriscoe.net/























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