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Internet Engineering Task Force (IETF) F. Gont Request for Comments: 6633 UTN-FRH / SI6 Networks Updates: 792, 1122, 1812 May 2012 Category: Standards Track ISSN: 2070-1721

             Deprecation of ICMP Source Quench Messages

Abstract

 This document formally deprecates the use of ICMP Source Quench
 messages by transport protocols, formally updating RFC 792, RFC 1122,
 and RFC 1812.

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 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/rfc6633.

Copyright Notice

 Copyright (c) 2012 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.  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.

Gont Standards Track [Page 1] RFC 6633 Deprecation of ICMP Source Quench May 2012

Table of Contents

 1. Introduction ....................................................2
 2. ICMP Source Quench Messages .....................................3
 3. Updating RFC 1122 ...............................................3
 4. Updating RFC 1812 ...............................................4
 5. Clarification for UDP, SCTP, and DCCP ...........................4
 6. General Advice to Transport Protocols ...........................4
 7. Recommendation Regarding RFC 1016 ...............................5
 8. Security Considerations .........................................5
 9. IANA Considerations .............................................5
 10. Acknowledgements ...............................................5
 11. References .....................................................6
    11.1. Normative References ......................................6
    11.2. Informative References ....................................7
 Appendix A.  Survey of Support of ICMP Source Quench in Some
              Popular TCP/IP Implementations ........................8

1. Introduction

 The ICMP specification [RFC0792] defined the ICMP Source Quench
 message (type 4, code 0), which was meant as a mechanism for
 congestion control.  ICMP Source Quench has been known to be an
 ineffective (and unfair) antidote for congestion, and generation of
 ICMP Source Quench messages by routers has been formally deprecated
 by [RFC1812] since 1995.  However, reaction to ICMP Source Quench
 messages in transport protocols has never been formally deprecated.

 This document formally deprecates reaction to ICMP Source Quench
 messages by transport protocols such as TCP [RFC0793], formally
 updating [RFC0792], [RFC1122], and [RFC1812].  Additionally, it
 provides a recommendation against the implementation of [RFC1016].
 The rationale for these specification updates is as follows:

 o  Processing of ICMP Source Quench messages by routers has been
    deprecated for nearly 17 years [RFC1812].

 o  Virtually all popular host implementations have removed support
    for ICMP Source Quench messages since (at least) 2005 [RFC5927].

 o  Widespread deployment of ICMP filtering makes it impossible to
    rely on ICMP Source Quench messages for congestion control.

 o  The IETF has moved away from ICMP Source Quench messages for
    congestion control (e.g., note the development of Explicit
    Congestion Notification (ECN) [RFC3168] and the fact that ICMPv6
    [RFC4443] does not even specify a Source Quench message).

Gont Standards Track [Page 2] RFC 6633 Deprecation of ICMP Source Quench May 2012

       ICMP Source Quench messages are not normally seen in the
       deployed Internet and were considered rare at least as far back
       as 1994 [Floyd1994].

 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 [RFC2119].

2. ICMP Source Quench Messages

 The ICMP specification [RFC0792] defined the ICMP Source Quench
 message (type 4, code 0), which was meant to provide a mechanism for
 congestion control.  The Host Requirements RFC [RFC1122] stated in
 Section 4.2.3.9 that hosts MUST react to ICMP Source Quench messages
 by slowing transmission on the connection, and further added that the
 RECOMMENDED procedure was to put the corresponding connection in the
 slow-start phase of TCP's congestion control algorithm [RFC5681].

 [RFC1812] noted that research suggested that ICMP Source Quench was
 an ineffective (and unfair) antidote for congestion, and formally
 deprecated the generation of ICMP Source Quench messages by routers,
 stating that routers SHOULD NOT send ICMP Source Quench messages in
 response to congestion.

 [RFC5927] discussed the use of ICMP Source Quench messages for
 performing "blind throughput-reduction" attacks, and noted that most
 TCP implementations silently ignore ICMP Source Quench messages.

 We note that TCP implements its own congestion control mechanisms
 [RFC5681] [RFC3168], which do not depend on ICMP Source Quench
 messages.

    It is interesting to note that ICMPv6 [RFC4443] does not specify a
    Source Quench message.

3. Updating RFC 1122

 This document hereby updates Section 3.2.2.3 of [RFC1122] as follows:

    A host MUST NOT send ICMP Source Quench messages.

    If a Source Quench message is received, the IP layer MAY silently
    discard it.

 Section 4.2.3.9 of [RFC1122] is updated as follows:

    TCP MUST silently discard any received ICMP Source Quench
    messages.

Gont Standards Track [Page 3] RFC 6633 Deprecation of ICMP Source Quench May 2012

 The consensus of the TSV WG was that there are no valid reasons for a
 host to generate or react to an ICMP Source Quench message in the
 current Internet.  The recommendation that a sender "MUST NOT" send
 an ICMP Source Quench message is because there is no known valid
 reason for a host to generate this message.  The only known impact of
 a sender ignoring this requirement is that it may necessarily consume
 network and endpoint resources.  Discarding ICMP Source Quench
 messages at the Internet layer (rather than at the transport layer)
 is a performance optimization that is permitted by this update.

4. Updating RFC 1812

 This document hereby updates Section 4.3.3.3 of [RFC1812] as follows:

    A router MUST ignore any ICMP Source Quench messages it receives.

 The consensus of the TSV WG was that there are no valid reasons for a
 router to react to ICMP Source Quench messages in the current
 Internet.

5. Clarification for UDP, SCTP, and DCCP

 UDP [RFC0768] did not explicitly specify support for ICMP Source
 Quench messages.  Hereby, we clarify that UDP endpoints MUST silently
 discard received ICMP Source Quench messages.

 It is understood that SCTP [RFC4960] and DCCP [RFC4340] did not
 specify support for processing received ICMP Source Quench messages.
 Hereby, we clarify that DCCP and SCTP endpoints MUST silently discard
 received ICMP Source Quench messages.

6. General Advice to Transport Protocols

 If a Source Quench message is received by any other transport-
 protocol instance, it MUST be silently ignored.

 The TSV WG is not aware of any mechanism that requires processing of
 these messages and therefore expects other transports to follow the
 recommendations in Section 3.  Note that since generation of ICMP
 Source Quench messages has been deprecated for many years, and since
 this document additionally deprecates reaction to ICMP Source Quench
 messages by IETF-specified transports, future applications cannot
 expect to receive these messages.

Gont Standards Track [Page 4] RFC 6633 Deprecation of ICMP Source Quench May 2012

7. Recommendation Regarding RFC 1016

 [RFC1016] describes an experimental approach to the handling of ICMP
 Source Quench messages in hosts that was considered in 1987.  Even
 though RFC 1016 has never been on the IETF Standards Track, for
 clarity and avoidance of doubt we note that the approach described in
 [RFC1016] MUST NOT be implemented.

8. Security Considerations

 ICMP Source Quench messages could be leveraged for performing blind
 throughput-reduction attacks against TCP and similar protocols.  This
 attack vector, along with possible countermeasures, has been
 discussed in great detail in [RFC5927] and [CPNI-TCP].  Silently
 ignoring ICMP Source Quench messages, as specified in this document,
 eliminates the aforementioned attack vector.

 For current TCP implementations, receipt of an ICMP Source Quench
 message should not result in security issues because, as noted in
 [RFC5927] and [CPNI-TCP], virtually all current versions of popular
 TCP implementations already silently ignore ICMP Source Quench
 messages.  This is also the case for SCTP and DCCP implementations.

 Hosts, security gateways, and firewalls MUST silently discard
 received ICMP Source Quench packets and SHOULD log such drops as a
 security fault with at least minimal details (IP Source Address, IP
 Destination Address, ICMP message type, and date/time the packet was
 seen).

    We note that security devices such as the Snort Network Intrusion
    Detection System (NIDS) have logged ICMP Source Quench messages as
    such for more than ten years [Anderson2002].

9. IANA Considerations

 IANA has marked ICMP type 4 (Source Quench) as "Deprecated" in the
 ICMP Parameters registry [ICMPPARREG] with a reference to this
 document.

10. Acknowledgements

 The author of this document would like to thank Ran Atkinson, who
 contributed text that was incorporated into this document and also
 provided valuable feedback on earlier versions of this document.

 The author of this document would like to thank (in alphabetical
 order) Fred Baker, David Black, Scott Bradner, James Carlson, Antonio
 De Simone, Wesley Eddy, Gorry Fairhurst, Alfred Hoenes, Mahesh

Gont Standards Track [Page 5] RFC 6633 Deprecation of ICMP Source Quench May 2012

 Jethanandani, Kathleen Moriarty, Carlos Pignataro, James Polk,
 Anantha Ramaiah, Randall Stewart, Dan Wing, and Andrew Yourtchenko,
 for providing valuable feedback on earlier versions of this document.
 This document has also benefited from discussions within the TCPM
 Working Group while working on [RFC5927].

 Fernando Gont wishes to thank Jorge Oscar Gont, Nelida Garcia, and
 Guillermo Gont for their love and support.

 Fernando Gont's attendance to IETF meetings was supported by ISOC's
 "Fellowship to the IETF" program.

11. References

11.1. Normative References

 [RFC0768]       Postel, J., "User Datagram Protocol", STD 6, RFC 768,
                 August 1980.

 [RFC0792]       Postel, J., "Internet Control Message Protocol",
                 STD 5, RFC 792, September 1981.

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

 [RFC1122]       Braden, R., "Requirements for Internet Hosts -
                 Communication Layers", STD 3, RFC 1122, October 1989.

 [RFC1812]       Baker, F., "Requirements for IP Version 4 Routers",
                 RFC 1812, June 1995.

 [RFC2119]       Bradner, S., "Key words for use in RFCs to Indicate
                 Requirement Levels", BCP 14, RFC 2119, March 1997.

 [RFC4340]       Kohler, E., Handley, M., and S. Floyd, "Datagram
                 Congestion Control Protocol (DCCP)", RFC 4340,
                 March 2006.

 [RFC4960]       Stewart, R., "Stream Control Transmission Protocol",
                 RFC 4960, September 2007.

 [RFC5681]       Allman, M., Paxson, V., and E. Blanton, "TCP
                 Congestion Control", RFC 5681, September 2009.

Gont Standards Track [Page 6] RFC 6633 Deprecation of ICMP Source Quench May 2012

11.2. Informative References

 [Anderson2002]  Anderson, D., Fong, M., and A. Valdes, "Heterogeneous
                 Sensor Correlation: A Case Study of Live Traffic
                 Analysis", Proceedings of the 3rd Annual IEEE
                 Information Assurance Workshop New York, NY, USA,
                 2002.

 [CPNI-TCP]      CPNI, "Security Assessment of the Transmission
                 Control Protocol (TCP)", 2009,
                 <http://www.gont.com.ar/papers/
                 tn-03-09-security-assessment-TCP.pdf>.

 [Floyd1994]     Floyd, S., "TCP and Explicit Congestion
                 Notification", ACM CCR New York, NY, Volume 24,
                 Issue 5, October 1994.

 [FreeBSD]       The FreeBSD Project, <http://www.freebsd.org>.

 [ICMPPARREG]    IANA, "Internet Control Message Protocol (ICMP)
                 Parameters",
                 <http://www.iana.org/assignments/icmp-parameters>.

 [Linux]         The Linux Project, <http://www.kernel.org>.

 [NetBSD]        The NetBSD Project, <http://www.netbsd.org>.

 [OpenBSD]       The OpenBSD Project, <http://www.openbsd.org>.

 [OpenSolaris]   OpenSolaris, <http://www.opensolaris.org>.

 [RFC1016]       Prue, W. and J. Postel, "Something a host could do
                 with source quench: The Source Quench Introduced
                 Delay (SQuID)", RFC 1016, July 1987.

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

 [RFC4443]       Conta, A., Deering, S., and M. Gupta, "Internet
                 Control Message Protocol (ICMPv6) for the Internet
                 Protocol Version 6 (IPv6) Specification", RFC 4443,
                 March 2006.

 [RFC5927]       Gont, F., "ICMP Attacks against TCP", RFC 5927,
                 July 2010.

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Appendix A. Survey of Support of ICMP Source Quench in Some Popular

           TCP/IP Implementations

 A large number of implementations completely ignore ICMP Source
 Quench messages meant for TCP connections.  This behavior has been
 implemented in, at least, Linux [Linux] since 2004, and in FreeBSD
 [FreeBSD], NetBSD [NetBSD], OpenBSD [OpenBSD], and Solaris 10 since
 2005.  Additionally, OpenSolaris [OpenSolaris] has always shipped
 with support for ICMP Source Quench messages disabled.

Author's Address

 Fernando Gont
 UTN-FRH / SI6 Networks
 Evaristo Carriego 2644
 Haedo, Provincia de Buenos Aires  1706
 Argentina

 Phone: +54 11 4650 8472
 EMail: fgont@si6networks.com
 URI:   http://www.si6networks.com

Gont Standards Track [Page 8]