Recommendation to Use the Ethernet Control Word
RFC 8469

Document Type RFC - Proposed Standard (November 2018; No errata)
Updates RFC 4448
Last updated 2018-11-14
Replaces draft-bryant-pals-ethernet-cw
Stream IETF
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Document shepherd Matthew Bocci
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IESG IESG state RFC 8469 (Proposed Standard)
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Send notices to Matthew Bocci <matthew.bocci@nokia.com>
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Internet Engineering Task Force (IETF)                         S. Bryant
Request for Comments: 8469                                      A. Malis
Updates: 4448                                                     Huawei
Category: Standards Track                                    I. Bagdonas
ISSN: 2070-1721                                                  Equinix
                                                           November 2018

            Recommendation to Use the Ethernet Control Word

Abstract

   The pseudowire (PW) encapsulation of Ethernet, as defined in
   RFC 4448, specifies that the use of the control word (CW) is
   optional.  In the absence of the CW, an Ethernet PW packet can be
   misidentified as an IP packet by a label switching router (LSR).
   This may lead to the selection of the wrong equal-cost multipath
   (ECMP) path for the packet, leading in turn to the misordering of
   packets.  This problem has become more serious due to the deployment
   of equipment with Ethernet Media Access Control (MAC) addresses that
   start with 0x4 or 0x6.  The use of the Ethernet PW CW addresses this
   problem.  This document RECOMMENDS the use of the Ethernet PW CW in
   all but exceptional circumstances.

   This document updates RFC 4448.

Status of This Memo

   This is an Internet Standards Track document.

   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).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8469.

Bryant, et al.               Standards Track                    [Page 1]
RFC 8469               Ethernet CW Recommendation          November 2018

Copyright Notice

   Copyright (c) 2018 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
   Provisions Relating to IETF Documents
   (https://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
   to this document.  Code Components extracted from this document must
   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. Specification of Requirements ...................................3
   3. Background ......................................................4
   4. Recommendation ..................................................5
   5. Equal-Cost Multipath (ECMP) .....................................5
   6. Mitigations .....................................................6
   7. Operational Considerations ......................................6
   8. Security Considerations .........................................7
   9. IANA Considerations .............................................7
   10. References .....................................................7
      10.1. Normative References ......................................7
      10.2. Informative References ....................................8
   Acknowledgments ....................................................9
   Authors' Addresses .................................................9

Bryant, et al.               Standards Track                    [Page 2]
RFC 8469               Ethernet CW Recommendation          November 2018

1.  Introduction

   The pseudowire (PW) encapsulation of Ethernet, as defined in
   [RFC4448], specifies that the use of the control word (CW) is
   optional.  It is common for label switching routers (LSRs) to search
   past the end of the label stack to determine whether the payload is
   an IP packet and then, if it is, select the next hop based on the
   so-called "five-tuple" (IP source address, IP destination address,
   protocol/next-header, transport-layer source port, and transport-
   layer destination port).  In the absence of a PW CW, an Ethernet PW
   packet can be misidentified as an IP packet by a label switching
   router (LSR) selecting the ECMP path based on the five-tuple.  This
   may lead to the selection of the wrong ECMP path for the packet,
   leading in turn to the misordering of packets.  Further discussion of
   this topic is published in [RFC4928].

   Flow misordering can also happen in a single-path scenario when
   traffic classification and differential forwarding treatment
   mechanisms are in use.  These errors occur when a forwarder
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