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Versions: 00 01 02 03 04 05 rfc7125                                     
IPFIX Working Group                                          B. Trammell
Internet-Draft                                                ETH Zurich
Intended status: Informational                                 P. Aitken
Expires: March 10, 2014                               Cisco Systems, Inc
                                                      September 06, 2013

        Revision of the tcpControlBits IPFIX Information Element


   This document revises the tcpControlBits IPFIX Information Element
   defined in [RFC5102] to reflect changes to the TCP Flags header field
   since [RFC0793].

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
   Task Force (IETF).  Note that other groups may also distribute
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   Internet-Drafts are draft documents valid for a maximum of six months
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 10, 2014.

Copyright Notice

   Copyright (c) 2013 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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   described in the Simplified BSD License.

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1.  Introduction

   The first 16 bits of the TCP header contain four bits of encoded
   header length as well as 12 bits of flags.  The least significant 6
   bits of these were defined in [RFC0793] as URG, ACK, PSH, RST, SYN,
   and FIN for TCP control.  Subsequently, [RFC3168] defined the CWR and
   ECE flags for Explicit Congestion Notification (ECN) negotiation and
   signaling; [RFC3540] additionally defined the NS flag for the ECN
   Nonce Sum.

   As defined in the IANA IPFIX Information Element Registry
   [IANA-IPFIX], taken from [RFC5102], the tcpControlBits Information
   Element for IPFIX [I-D.ietf-ipfix-protocol-rfc5101bis] only covers
   the original six bits from [RFC0793].  To allow IPFIX to be used to
   measure the use of ECN, and to bring the IPFIX Information Element
   definition in line with the current definition of the TCP Flags
   header field, it is necessary to revise this definition.

   The revised definition of the Information Element in Section 2 was
   developed and approved through the IE-DOCTORS process
   [I-D.ietf-ipfix-ie-doctors] in August 2013.  Section 5.1 of
   [I-D.ietf-ipfix-ie-doctors] states "This process should not in any
   way be construed as allowing the IE-DOCTORS to overrule IETF
   consensus.  Specifically, Information Elements in the IANA IE
   registry which were added with IETF consensus require IETF consensus
   for revision or deprecation".  Since the tcpControlBits Information
   Element was defined in [RFC5102], an IETF Proposed Standard, any
   revision of this Information Element definition requires IETF
   Consensus.  The publication of this document fulfills that

   The following section defines the revised tcpControlBits Information
   Element as in Section 9.1 of [I-D.ietf-ipfix-ie-doctors].

2.  The tcpControlBits Information Element

   ElementId:   6
   Data Type:   unsigned16
   Data Type Semantics:   flags
   Description:   TCP control bits observed for the packets of this
      Flow.  This information is encoded as a bit field; for each TCP
      control bit, there is a bit in this set.  The bit is set to 1 if
      any observed packet of this Flow has the corresponding TCP control
      bit set to 1.  The bit is cleared to 0 otherwise.

      The values of each bit are as follows, following the definition of
      the bits in the TCP header below:

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Internet-Draft            IPFIX tcpControlBits            September 2013

     0   1   2   3   4   5   6   7   8   9  10  11  12  13  14  15
   |               |           | N | C | E | U | A | P | R | S | F |
   | Header Length | Reserved  | S | W | C | R | C | S | S | Y | I |
   |               |           |   | R | E | G | K | H | T | N | N |

   bit    flag
   value  name  description
   0x8000       Zero (see tcpHeaderLength)
   0x4000       Zero (see tcpHeaderLength)
   0x2000       Zero (see tcpHeaderLength)
   0x1000       Zero (see tcpHeaderLength)
   0x0800       Future Use
   0x0400       Future Use
   0x0200       Future Use
   0x0100   NS  ECN Nonce Sum
   0x0080  CWR  Congestion Window Reduced
   0x0040  ECE  ECN Echo
   0x0020  URG  Urgent Pointer field significant
   0x0010  ACK  Acknowledgment field significant
   0x0008  PSH  Push Function
   0x0004  RST  Reset the connection
   0x0002  SYN  Synchronize sequence numbers
   0x0001  FIN  No more data from sender

      As the most significant four bits of this header field are used to
      encode the TCP header length, they must be exported as zero and
      must be ignored by the collector.

      Each of the three future use bits (0x800, 0x400, and 0x200) should
      be exported as one if the coresponding bit is observed in the TCP
      headers of the packets of this Flow, as they may be subsequent to
      a future update of [RFC0793].

      If exported as a single octet with reduced length encoding, this
      Information Element covers the low-order octet of this field (i.e,
      bits 0x80 to 0x01), omitting the ECN Nonce Sum and the three
      Future Use bits.  A collector receiving this Information Element
      with reduced length encoding must not assume anything about the
      content of these four bits.

      Note that previous revisions of this Information Element's
      definition specified that the CWR and ECE bits must be exported as
      zero, even if observed.  Collectors should therefore not assume
      that a value of zero for these bits in this Information Element

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Internet-Draft            IPFIX tcpControlBits            September 2013

      indicates the bits were never set in the observed traffic,
      especially if these bits are zero in every Flow Record sent by a
      given exporter.
   References:   [RFC0793][RFC3168][RFC3540]
   Revision:  1

3.  IANA Considerations

   IANA will update the definition of the tcpControlBits Information
   Element in the the IANA IPFIX Information Element Registry
   [IANA-IPFIX] to reflect the changes in Section 2 above.

4.  Security and Privacy Considerations

   This document has no security or privacy considerations; the security
   considerations for IPFIX [I-D.ietf-ipfix-protocol-rfc5101bis] apply.

5.  Acknowledgments

   Thanks to Andrew Feren for comments on the revised definition.  This
   work is partially supported by the European Commission under grant
   agreement FP7-ICT-318627 mPlane; this does not imply endorsement by
   the Commission.

6.  References

6.1.  Normative References

              Claise, B. and B. Trammell, "Specification of the IP Flow
              Information eXport (IPFIX) Protocol for the Exchange of
              Flow Information", draft-ietf-ipfix-protocol-rfc5101bis-10
              (work in progress), July 2013.

              Trammell, B. and B. Claise, "Guidelines for Authors and
              Reviewers of IPFIX Information Elements", draft-ietf-
              ipfix-ie-doctors-07 (work in progress), October 2012.

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7, RFC
              793, September 1981.

   [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
              of Explicit Congestion Notification (ECN) to IP", RFC
              3168, September 2001.

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   [RFC3540]  Spring, N., Wetherall, D., and D. Ely, "Robust Explicit
              Congestion Notification (ECN) Signaling with Nonces", RFC
              3540, June 2003.

6.2.  Informative References

   [RFC5102]  Quittek, J., Bryant, S., Claise, B., Aitken, P., and J.
              Meyer, "Information Model for IP Flow Information Export",
              RFC 5102, January 2008.

              Internet Assigned Numbers Authority, ., "IP Flow
              Information Export Information Elements
              (http://www.iana.org/assignments/ipfix)", .

Authors' Addresses

   Brian Trammell
   Swiss Federal Institute of Technology Zurich
   Gloriastrasse 35
   8092 Zurich

   Phone: +41 44 632 70 13
   Email: trammell@tik.ee.ethz.ch

   Paul Aitken
   Cisco Systems, Inc.
   96 Commercial Quay
   Commercial Street, Edinburgh EH6 6LX
   United Kingdom

   Phone: +44 131 561 3616
   Email: paitken@cisco.com

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