Really Explicit Congestion Notification (RECN)
RFC 7514

Document Type RFC - Experimental (April 2015; No errata)
Last updated 2015-04-01
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Independent Submission                                         M. Luckie
Request for Comments: 7514                                         CAIDA
Category: Experimental                                      1 April 2015
ISSN: 2070-1721

             Really Explicit Congestion Notification (RECN)

Abstract

   This document proposes a new ICMP message that a router or host may
   use to advise a host to reduce the rate at which it sends, in cases
   where the host ignores other signals provided by packet loss and
   Explicit Congestion Notification (ECN).

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for examination, experimental implementation, and
   evaluation.

   This document defines an Experimental Protocol for the Internet
   community.  This is a contribution to the RFC Series, independently
   of any other RFC stream.  The RFC Editor has chosen to publish this
   document at its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not 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
   http://www.rfc-editor.org/info/rfc7514.

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
   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
   to this document.

Luckie                        Experimental                      [Page 1]
RFC 7514                          RECN                      1 April 2015

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   2
   2.  RECN Message Format . . . . . . . . . . . . . . . . . . . . .   2
     2.1.  Advice to Implementers  . . . . . . . . . . . . . . . . .   3
     2.2.  Relationship to ICMP Source Quench  . . . . . . . . . . .   4
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   4
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  Normative References  . . . . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   5

1.  Introduction

   The deployment of Explicit Congestion Notification (ECN) [RFC3168]
   remains stalled.  While most operating systems support ECN, it is
   currently disabled by default because of fears that enabling ECN will
   break transport protocols.  This document proposes a new ICMP message
   that a router or host may use to advise a host to reduce the rate at
   which it sends, in cases where the host ignores other signals such as
   packet loss and ECN.  We call this message the "Really Explicit
   Congestion Notification" (RECN) message because it delivers a less
   subtle indication of congestion than packet loss and ECN.

1.1.  Requirements Language

   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 RFC 2119 [RFC2119].

2.  RECN Message Format

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Type      |     Code      |          Checksum             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Explicit Notification                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           As much of the invoking packet as possible          |
   +           without the ICMP packet exceeding 576 bytes         |
   |               in IPv4 or the minimum MTU in IPv6              |

   Type

      IPv4: 4

      IPv6: 201

Luckie                        Experimental                      [Page 2]
RFC 7514                          RECN                      1 April 2015

   Code

      0

   Checksum

      The checksum is the 16-bit ones's complement of the one's
      complement sum of the ICMP message starting with the ICMP type
      field.  When an RECN message is encapsulated in an IPv6 packet,
      the computation includes a "pseudo-header" of IPv6 header fields
      as specified in Section 8.1 of [RFC2460].  For computing the
      checksum, the checksum field is first set to zero.

   Explicit Notification

      A 4-byte value that conveys an explicit notification in the ASCII
      format defined in [RFC20].  This field MUST NOT be set to zero.
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