6633
PROPOSED STANDARD
Deprecation of ICMP Source Quench Messages
Authors: F. Gont
Date: May 2012
Area: wit
Working Group: tsvwg
Stream: IETF
Updates:
RFC 792
Abstract
This document formally deprecates the use of ICMP Source Quench messages by transport protocols, formally updating RFC 792, RFC 1122, and RFC 1812. [STANDARDS-TRACK]
RFC 6633
PROPOSED STANDARD
Internet Engineering Task Force (IETF) F. Gont
Request for Comments: 6633 UTN-FRH / SI6 Networks
Updates: <a href="./rfc792">792</a>, <a href="./rfc1122">1122</a>, <a href="./rfc1812">1812</a> May 2012
Category: Standards Track
ISSN: 2070-1721
<span class="h1">Deprecation of ICMP Source Quench Messages</span>
Abstract
This document formally deprecates the use of ICMP Source Quench
messages by transport protocols, formally updating <a href="./rfc792">RFC 792</a>, <a href="./rfc1122">RFC 1122</a>,
and <a href="./rfc1812">RFC 1812</a>.
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 <a href="./rfc5741#section-2">Section 2 of RFC 5741</a>.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
<a href="https://www.rfc-editor.org/info/rfc6633">http://www.rfc-editor.org/info/rfc6633</a>.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a> and the IETF Trust's Legal
Provisions Relating to IETF Documents
(<a href="http://trustee.ietf.org/license-info">http://trustee.ietf.org/license-info</a>) in effect on the date of
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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.
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Table of Contents
<a href="#section-1">1</a>. Introduction ....................................................<a href="#page-2">2</a>
<a href="#section-2">2</a>. ICMP Source Quench Messages .....................................<a href="#page-3">3</a>
<a href="#section-3">3</a>. Updating <a href="./rfc1122">RFC 1122</a> ...............................................<a href="#page-3">3</a>
<a href="#section-4">4</a>. Updating <a href="./rfc1812">RFC 1812</a> ...............................................<a href="#page-4">4</a>
<a href="#section-5">5</a>. Clarification for UDP, SCTP, and DCCP ...........................<a href="#page-4">4</a>
<a href="#section-6">6</a>. General Advice to Transport Protocols ...........................<a href="#page-4">4</a>
<a href="#section-7">7</a>. Recommendation Regarding <a href="./rfc1016">RFC 1016</a> ...............................<a href="#page-5">5</a>
<a href="#section-8">8</a>. Security Considerations .........................................<a href="#page-5">5</a>
<a href="#section-9">9</a>. IANA Considerations .............................................<a href="#page-5">5</a>
<a href="#section-10">10</a>. Acknowledgements ...............................................<a href="#page-5">5</a>
<a href="#section-11">11</a>. References .....................................................<a href="#page-6">6</a>
<a href="#section-11.1">11.1</a>. Normative References ......................................<a href="#page-6">6</a>
<a href="#section-11.2">11.2</a>. Informative References ....................................<a href="#page-7">7</a>
<a href="#appendix-A">Appendix A</a>. Survey of Support of ICMP Source Quench in Some
Popular TCP/IP Implementations ........................<a href="#page-8">8</a>
<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>. Introduction</span>
The ICMP specification [<a href="./rfc0792" title=""Internet Control Message Protocol"">RFC0792</a>] 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 [<a href="./rfc1812" title=""Requirements for IP Version 4 Routers"">RFC1812</a>] 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 [<a href="./rfc0793" title=""Transmission Control Protocol"">RFC0793</a>], formally
updating [<a href="./rfc0792" title=""Internet Control Message Protocol"">RFC0792</a>], [<a href="./rfc1122" title=""Requirements for Internet Hosts - Communication Layers"">RFC1122</a>], and [<a href="./rfc1812" title=""Requirements for IP Version 4 Routers"">RFC1812</a>]. Additionally, it
provides a recommendation against the implementation of [<a href="./rfc1016" title=""Something a host could do with source quench: The Source Quench Introduced Delay (SQuID)"">RFC1016</a>].
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 [<a href="./rfc1812" title=""Requirements for IP Version 4 Routers"">RFC1812</a>].
o Virtually all popular host implementations have removed support
for ICMP Source Quench messages since (at least) 2005 [<a href="./rfc5927" title=""ICMP Attacks against TCP"">RFC5927</a>].
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) [<a href="./rfc3168" title=""The Addition of Explicit Congestion Notification (ECN) to IP"">RFC3168</a>] and the fact that ICMPv6
[<a href="./rfc4443" title=""Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification"">RFC4443</a>] does not even specify a Source Quench message).
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ICMP Source Quench messages are not normally seen in the
deployed Internet and were considered rare at least as far back
as 1994 [<a href="#ref-Floyd1994" title=""TCP and Explicit Congestion Notification"">Floyd1994</a>].
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 [<a href="./rfc2119" title=""Key words for use in RFCs to Indicate Requirement Levels"">RFC2119</a>].
<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>. ICMP Source Quench Messages</span>
The ICMP specification [<a href="./rfc0792" title=""Internet Control Message Protocol"">RFC0792</a>] defined the ICMP Source Quench
message (type 4, code 0), which was meant to provide a mechanism for
congestion control. The Host Requirements RFC [<a href="./rfc1122" title=""Requirements for Internet Hosts - Communication Layers"">RFC1122</a>] stated in
<a href="#section-4.2.3.9">Section 4.2.3.9</a> 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 [<a href="./rfc5681" title=""TCP Congestion Control"">RFC5681</a>].
[<a id="ref-RFC1812">RFC1812</a>] 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.
[<a id="ref-RFC5927">RFC5927</a>] 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
[<a href="./rfc5681" title=""TCP Congestion Control"">RFC5681</a>] [<a href="./rfc3168" title=""The Addition of Explicit Congestion Notification (ECN) to IP"">RFC3168</a>], which do not depend on ICMP Source Quench
messages.
It is interesting to note that ICMPv6 [<a href="./rfc4443" title=""Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification"">RFC4443</a>] does not specify a
Source Quench message.
<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>. Updating <a href="./rfc1122">RFC 1122</a></span>
This document hereby updates <a href="./rfc1122#section-3.2.2.3">Section 3.2.2.3 of [RFC1122]</a> 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.
<a href="./rfc1122#section-4.2.3.9">Section 4.2.3.9 of [RFC1122]</a> is updated as follows:
TCP MUST silently discard any received ICMP Source Quench
messages.
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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.
<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>. Updating <a href="./rfc1812">RFC 1812</a></span>
This document hereby updates <a href="./rfc1812#section-4.3.3.3">Section 4.3.3.3 of [RFC1812]</a> 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.
<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>. Clarification for UDP, SCTP, and DCCP</span>
UDP [<a href="./rfc0768" title=""User Datagram Protocol"">RFC0768</a>] 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 [<a href="./rfc4960" title=""Stream Control Transmission Protocol"">RFC4960</a>] and DCCP [<a href="./rfc4340" title=""Datagram Congestion Control Protocol (DCCP)"">RFC4340</a>] 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.
<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>. General Advice to Transport Protocols</span>
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 <a href="#section-3">Section 3</a>. 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.
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<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>. Recommendation Regarding <a href="./rfc1016">RFC 1016</a></span>
[<a id="ref-RFC1016">RFC1016</a>] describes an experimental approach to the handling of ICMP
Source Quench messages in hosts that was considered in 1987. Even
though <a href="./rfc1016">RFC 1016</a> has never been on the IETF Standards Track, for
clarity and avoidance of doubt we note that the approach described in
[<a href="./rfc1016" title=""Something a host could do with source quench: The Source Quench Introduced Delay (SQuID)"">RFC1016</a>] MUST NOT be implemented.
<span class="h2"><a class="selflink" id="section-8" href="#section-8">8</a>. Security Considerations</span>
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 [<a href="./rfc5927" title=""ICMP Attacks against TCP"">RFC5927</a>] and [<a href="#ref-CPNI-TCP" title=""Security Assessment of the Transmission Control Protocol (TCP)"">CPNI-TCP</a>]. 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
[<a href="./rfc5927" title=""ICMP Attacks against TCP"">RFC5927</a>] and [<a href="#ref-CPNI-TCP" title=""Security Assessment of the Transmission Control Protocol (TCP)"">CPNI-TCP</a>], 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 [<a href="#ref-Anderson2002" title=""Heterogeneous Sensor Correlation: A Case Study of Live Traffic Analysis"">Anderson2002</a>].
<span class="h2"><a class="selflink" id="section-9" href="#section-9">9</a>. IANA Considerations</span>
IANA has marked ICMP type 4 (Source Quench) as "Deprecated" in the
ICMP Parameters registry [<a href="#ref-ICMPPARREG" title=""Internet Control Message Protocol (ICMP) Parameters"">ICMPPARREG</a>] with a reference to this
document.
<span class="h2"><a class="selflink" id="section-10" href="#section-10">10</a>. Acknowledgements</span>
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
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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 [<a href="./rfc5927" title=""ICMP Attacks against TCP"">RFC5927</a>].
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.
<span class="h2"><a class="selflink" id="section-11" href="#section-11">11</a>. References</span>
<span class="h3"><a class="selflink" id="section-11.1" href="#section-11.1">11.1</a>. Normative References</span>
[<a id="ref-RFC0768">RFC0768</a>] Postel, J., "User Datagram Protocol", STD 6, <a href="./rfc768">RFC 768</a>,
August 1980.
[<a id="ref-RFC0792">RFC0792</a>] Postel, J., "Internet Control Message Protocol",
STD 5, <a href="./rfc792">RFC 792</a>, September 1981.
[<a id="ref-RFC0793">RFC0793</a>] Postel, J., "Transmission Control Protocol", STD 7,
<a href="./rfc793">RFC 793</a>, September 1981.
[<a id="ref-RFC1122">RFC1122</a>] Braden, R., "Requirements for Internet Hosts -
Communication Layers", STD 3, <a href="./rfc1122">RFC 1122</a>, October 1989.
[<a id="ref-RFC1812">RFC1812</a>] Baker, F., "Requirements for IP Version 4 Routers",
<a href="./rfc1812">RFC 1812</a>, June 1995.
[<a id="ref-RFC2119">RFC2119</a>] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>, March 1997.
[<a id="ref-RFC4340">RFC4340</a>] Kohler, E., Handley, M., and S. Floyd, "Datagram
Congestion Control Protocol (DCCP)", <a href="./rfc4340">RFC 4340</a>,
March 2006.
[<a id="ref-RFC4960">RFC4960</a>] Stewart, R., "Stream Control Transmission Protocol",
<a href="./rfc4960">RFC 4960</a>, September 2007.
[<a id="ref-RFC5681">RFC5681</a>] Allman, M., Paxson, V., and E. Blanton, "TCP
Congestion Control", <a href="./rfc5681">RFC 5681</a>, September 2009.
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<span class="h3"><a class="selflink" id="section-11.2" href="#section-11.2">11.2</a>. Informative References</span>
[<a id="ref-Anderson2002">Anderson2002</a>] 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.
[<a id="ref-CPNI-TCP">CPNI-TCP</a>] CPNI, "Security Assessment of the Transmission
Control Protocol (TCP)", 2009,
<<a href="http://www.gont.com.ar/papers/tn-03-09-security-assessment-TCP.pdf">http://www.gont.com.ar/papers/</a>
<a href="http://www.gont.com.ar/papers/tn-03-09-security-assessment-TCP.pdf">tn-03-09-security-assessment-TCP.pdf</a>>.
[<a id="ref-Floyd1994">Floyd1994</a>] Floyd, S., "TCP and Explicit Congestion
Notification", ACM CCR New York, NY, Volume 24,
Issue 5, October 1994.
[<a id="ref-FreeBSD">FreeBSD</a>] The FreeBSD Project, <<a href="http://www.freebsd.org">http://www.freebsd.org</a>>.
[<a id="ref-ICMPPARREG">ICMPPARREG</a>] IANA, "Internet Control Message Protocol (ICMP)
Parameters",
<<a href="http://www.iana.org/assignments/icmp-parameters">http://www.iana.org/assignments/icmp-parameters</a>>.
[<a id="ref-Linux">Linux</a>] The Linux Project, <<a href="http://www.kernel.org">http://www.kernel.org</a>>.
[<a id="ref-NetBSD">NetBSD</a>] The NetBSD Project, <<a href="http://www.netbsd.org">http://www.netbsd.org</a>>.
[<a id="ref-OpenBSD">OpenBSD</a>] The OpenBSD Project, <<a href="http://www.openbsd.org">http://www.openbsd.org</a>>.
[<a id="ref-OpenSolaris">OpenSolaris</a>] OpenSolaris, <<a href="http://www.opensolaris.org">http://www.opensolaris.org</a>>.
[<a id="ref-RFC1016">RFC1016</a>] Prue, W. and J. Postel, "Something a host could do
with source quench: The Source Quench Introduced
Delay (SQuID)", <a href="./rfc1016">RFC 1016</a>, July 1987.
[<a id="ref-RFC3168">RFC3168</a>] Ramakrishnan, K., Floyd, S., and D. Black, "The
Addition of Explicit Congestion Notification (ECN) to
IP", <a href="./rfc3168">RFC 3168</a>, September 2001.
[<a id="ref-RFC4443">RFC4443</a>] Conta, A., Deering, S., and M. Gupta, "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", <a href="./rfc4443">RFC 4443</a>,
March 2006.
[<a id="ref-RFC5927">RFC5927</a>] Gont, F., "ICMP Attacks against TCP", <a href="./rfc5927">RFC 5927</a>,
July 2010.
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<span class="h2"><a class="selflink" id="appendix-A" href="#appendix-A">Appendix A</a>. Survey of Support of ICMP Source Quench in Some Popular</span>
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 [<a href="#ref-Linux">Linux</a>] since 2004, and in FreeBSD
[<a href="#ref-FreeBSD">FreeBSD</a>], NetBSD [<a href="#ref-NetBSD">NetBSD</a>], OpenBSD [<a href="#ref-OpenBSD">OpenBSD</a>], and Solaris 10 since
2005. Additionally, OpenSolaris [<a href="#ref-OpenSolaris">OpenSolaris</a>] 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: [email protected]
URI: <a href="http://www.si6networks.com">http://www.si6networks.com</a>
Gont Standards Track [Page 8]
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