Revision of the tcpControlBits IP Flow Information Export (IPFIX) Information Element
RFC 7125

Document Type RFC - Informational (February 2014; No errata)
Authors Brian Trammell  , Paul Aitken
Last updated 2015-10-14
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Internet Engineering Task Force (IETF)                       B. Trammell
Request for Comments: 7125                                    ETH Zurich
Category: Informational                                        P. Aitken
ISSN: 2070-1721                                       Cisco Systems, Inc
                                                           February 2014

                     Revision of the tcpControlBits
         IP Flow Information Export (IPFIX) Information Element


   This document revises the tcpControlBits IP Flow Information Export
   (IPFIX) Information Element as originally defined in RFC 5102 to
   reflect changes to the TCP Flags header field since RFC 793.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

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Trammell & Aitken             Informational                     [Page 1]
RFC 7125                  IPFIX tcpControlBits             February 2014

1.  Introduction

   Octets 12 and 13 (counting from zero) of the TCP header encode the
   data offset (header length) in 4 bits, 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 [RFC7011] only covers the original 6 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 3 was
   developed and approved through the IE-DOCTORS process [RFC7013] in
   August 2013.  Section 5.1 of [RFC7013] 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
   Information Element registry that were added with IETF consensus
   require IETF consensus for revision or deprecation".  Since the
   tcpControlBits Information Element was originally defined in
   [RFC5102], an IETF Proposed Standard, any revision of this
   Information Element definition requires IETF Consensus.  The
   publication of this document fulfills that requirement.

   Section 3 defines the revised tcpControlBits Information Element as
   in Section 9.1 of [RFC7013].

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this document are to be interpreted as described in

3.  The tcpControlBits Information Element

   ElementId:  6

   Data Type:  unsigned16

   Data Type Semantics:  flags

Trammell & Aitken             Informational                     [Page 2]
RFC 7125                  IPFIX tcpControlBits             February 2014

   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 shown below, per the definition of the
      bits in the TCP header [RFC0793] [RFC3168] [RFC3540]:

       MSb                                                         LSb
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