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rfc:rfc7514

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
 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.
 Description
    An RECN message SHOULD be sent by a router in response to a host
    that is generating traffic at a rate persistently unfair to other
    competing flows and that has not reacted to previous packet losses
    or ECN marks.
    The contents of an RECN message MUST be conveyed to the user
    responsible for the traffic.  Precisely how this is accomplished
    will depend on the capabilities of the host.  If text-to-speech
    capabilities are available, the contents should be converted to
    sound form and audibly rendered.  If the system is currently
    muted, a pop-up message will suffice.

2.1. Advice to Implementers

 As the Explicit Notification field is only 4 bytes, it is not
 required that the word be null terminated.  A client implementation
 should be careful not to use more than those 4 bytes.  If a router
 chooses a word less than 4 bytes in size, it should null-terminate
 that word.
 A router should not necessarily send an RECN message every time it
 discards a packet due to congestion.  Rather, a router should send
 these messages whenever it discards a burst of packets from a single
 sender.  For every packet a router discards in a single burst, it
 should send an RECN message.  A router may form short sentences
 composed of different 4-byte words, and a host should play these
 sentences back to the user.  A router may escalate the content in the
 Explicit Notification field if it determines that a sender has not

Luckie Experimental [Page 3] RFC 7514 RECN 1 April 2015

 adjusted its transmission rate in response to previous RECN messages.
 There is no upper bound on the intensity of the escalation, either in
 content or sentence length.

2.2. Relationship to ICMP Source Quench

 The RECN message was inspired by the ICMP Source Quench message,
 which is now deprecated [RFC6633].  Because the RECN message uses a
 similar approach, an RECN message uses the same ICMP type when
 encapsulated in IPv4 as was used by the ICMP Source Quench message.

3. IANA Considerations

 This is an Experimental RFC; the experiment will conclude two years
 after the publication of this RFC.  During the experiment,
 implementers are free to use words of their own choosing (up to four
 letters) in RECN messages.  If RECN becomes a Standard of any kind, a
 list of allowed words will be maintained in an IANA registry.  There
 are no IANA actions required at this time.

4. Security Considerations

 ICMP messages may be used in various attacks [RFC5927].  An attacker
 may use the RECN message to cause a host to reduce their transmission
 rate for no reason.  To prevent such an attack, a host must ensure
 the quoted message corresponds to an active flow on the system, and
 an attacker MUST set the security flag defined in [RFC3514] to 1 when
 the RECN message is carried in an IPv4 packet.

5. Normative References

 [RFC20]    Cerf, V., "ASCII format for network interchange", STD 80,
            RFC 20, October 1969,
            <http://www.rfc-editor.org/info/rfc20>.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997,
            <http://www.rfc-editor.org/info/rfc2119>.
 [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
            (IPv6) Specification", RFC 2460, December 1998,
            <http://www.rfc-editor.org/info/rfc2460>.
 [RFC3168]  Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
            of Explicit Congestion Notification (ECN) to IP", RFC
            3168, September 2001,
            <http://www.rfc-editor.org/info/rfc3168>.

Luckie Experimental [Page 4] RFC 7514 RECN 1 April 2015

 [RFC3514]  Bellovin, S., "The Security Flag in the IPv4 Header", RFC
            3514, April 2003,
            <http://www.rfc-editor.org/info/rfc3514>.
 [RFC5927]  Gont, F., "ICMP Attacks against TCP", RFC 5927, July 2010,
            <http://www.rfc-editor.org/info/rfc5927>.
 [RFC6633]  Gont, F., "Deprecation of ICMP Source Quench Messages",
            RFC 6633, May 2012,
            <http://www.rfc-editor.org/info/rfc6633>.

Author's Address

 Matthew Luckie
 CAIDA
 University of California, San Diego
 9500 Gilman Drive
 La Jolla, CA  92093-0505
 United States
 EMail: mjl@caida.org

Luckie Experimental [Page 5]

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