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Internet Engineering Task Force (IETF)                          M. Shore
Request for Comments: 7279                          No Mountain Software
BCP: 189                                                    C. Pignataro
Category: Best Current Practice                      Cisco Systems, Inc.
ISSN: 2070-1721                                                 May 2014

         An Acceptable Use Policy for New ICMP Types and Codes


   In this document we provide a basic description of ICMP's role in the
   IP stack and some guidelines for future use.

   This document is motivated by concerns about lack of clarity
   concerning when to add new Internet Control Message Protocol (ICMP)
   types and/or codes.  These concerns have highlighted a need to
   describe policies for when adding new features to ICMP is desirable
   and when it is not.

Status of This Memo

   This memo documents an Internet Best Current Practice.

   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
   BCPs 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

Copyright Notice

   Copyright (c) 2014 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.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Acceptable Use Policy . . . . . . . . . . . . . . . . . . . .   2
     2.1.  Classification of Existing Message Types  . . . . . . . .   3
       2.1.1.  ICMP Use as a Routing Protocol  . . . . . . . . . . .   6
       2.1.2.  A Few Notes on RPL  . . . . . . . . . . . . . . . . .   6
     2.2.  Applications Using ICMP . . . . . . . . . . . . . . . . .   7
     2.3.  Extending ICMP  . . . . . . . . . . . . . . . . . . . . .   7
     2.4.  ICMPv4 vs. ICMPv6 . . . . . . . . . . . . . . . . . . . .   7
   3.  ICMP's Role in the Internet . . . . . . . . . . . . . . . . .   7
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   5.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     6.1.  Normative references  . . . . . . . . . . . . . . . . . .   8
     6.2.  Informative references  . . . . . . . . . . . . . . . . .   9

1.  Introduction

   There has been some recent concern expressed about a lack of clarity
   around when new message types and codes should be added to ICMP
   (including ICMPv4 [RFC0792] and ICMPv6 [RFC4443]).  We lay out a
   policy regarding when (and when not) to move functionality into ICMP.

   This document is the result of discussions among ICMP experts within
   the Operations and Management (OPS) area's IP Diagnostics Technical
   Interest Group [DIAGNOSTICS] and concerns expressed by the OPS area

   Note that this document does not supercede the "IANA Allocation
   Guidelines For Values In the Internet Protocol and Related Headers"
   [RFC2780], which specifies best practices and processes for the
   allocation of values in the IANA registries but does not describe the
   policies to be applied in the standards process.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

2.  Acceptable Use Policy

   In this document, we describe an acceptable use policy for new ICMP
   message types and codes, and provide some background about the

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   In summary, any future message types added to ICMP should be limited
   to two broad categories:

   1.  to inform a datagram's originator that a forwarding plane anomaly
       has been encountered downstream.  The datagram originator must be
       able to determine whether or not the datagram was discarded by
       examining the ICMP message.

   2.  to discover and convey dynamic information about a node (other
       than information usually carried in routing protocols), to
       discover and convey network-specific parameters, and to discover
       on-link routers and hosts.

   Normally, ICMP SHOULD NOT be used to implement a general-purpose
   routing or network management protocol.  However, ICMP does have a
   role to play in conveying dynamic information about a network, which
   would belong in category 2 above.

2.1.  Classification of Existing Message Types

   This section provides a rough breakdown of existing message types
   according to the taxonomy described in Section 2 at the time of

   IPv4 forwarding plane anomaly reporting:

      3:   Destination Unreachable

      4:   Source Quench (Deprecated)

      6:   Alternate Host Address (Deprecated)

      11:  Time Exceeded

      12:  Parameter Problem

      31:  Datagram Conversion Error (Deprecated)

   IPv4 router or host discovery:

      0:   Echo Reply

      5:   Redirect

      8:   Echo

      9:   Router Advertisement

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      10:  Router Solicitation

      13:  Timestamp

      14:  Timestamp Reply

      15:  Information Request (Deprecated)

      16:  Information Reply (Deprecated)

      17:  Address Mask Request (Deprecated)

      18:  Address Mask Reply (Deprecated)

      30:  Traceroute (Deprecated)

      32:  Mobile Host Redirect (Deprecated)

      33:  IPv6 Where-Are-You (Deprecated)

      34:  IPv6 I-Am-Here (Deprecated)

      35:  Mobile Registration Request (Deprecated)

      36:  Mobile Registration Reply (Deprecated)

      37:  Domain Name Request (Deprecated)

      38:  Domain Name Reply (Deprecated)

      39:  SKIP (Deprecated)

      40:  Photuris

      41:  ICMP messages utilized by experimental mobility protocols
           such as Seamoby

   Please note that some ICMP message types were formally deprecated by

   IPv6 forwarding plane anomaly reporting:

      1:   Destination Unreachable

      2:   Packet Too Big

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      3:   Time Exceeded

      4:   Parameter Problem

      150: ICMP messages utilized by experimental mobility protocols
           such as Seamoby

   IPv6 router or host discovery:

      128: Echo Request

      129: Echo Reply

      130: Multicast Listener Query

      131: Multicast Listener Report

      132: Multicast Listener Done

      133: Router Solicitation

      134: Router Advertisement

      135: Neighbor Solicitation

      136: Neighbor Advertisement

      137: Redirect Message

      138: Router Renumbering

      139: ICMP Node Information Query

      140: ICMP Node Information Response

      141: Inverse Neighbor Discovery Solicitation Message

      142: Inverse Neighbor Discovery Advertisement Message

      143: Version 2 Multicast Listener Report

      144: Home Agent Address Discovery Request Message

      145: Home Agent Address Discovery Reply Message

      146: Mobile Prefix Solicitation

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      147: Mobile Prefix Advertisement

      148: Certification Path Solicitation Message

      149: Certification Path Advertisement Message

      150: ICMP messages utilized by experimental mobility protocols
           such as Seamoby

      151: Multicast Router Advertisement

      152: Multicast Router Solicitation

      153: Multicast Router Termination

      154: FMIPv6 Messages

      155: RPL Control Message

2.1.1.  ICMP Use as a Routing Protocol

   As mentioned in Section 2, using ICMP as a general-purpose routing or
   network management protocol is not advisable and SHOULD NOT be used
   that way.

   ICMP has a role in the Internet as an integral part of the IP layer;
   it is not as a routing protocol or as a transport protocol for other
   layers including routing information.  From a more pragmatic
   perspective, some of the key characteristics of ICMP make it a less-
   than-ideal choice for a routing protocol.  These key characteristics
   include that ICMP is frequently filtered, is not authenticated, and
   is easily spoofed.  In addition, specialist hardware processing of
   ICMP would disrupt the deployment of an ICMP-based routing or
   management protocol.

2.1.2.  A Few Notes on RPL

   RPL, the IPv6 routing protocol for low-power and lossy networks (see
   [RFC6550]) uses ICMP as a transport.  In this regard, it is an
   exception among the ICMP message types.  Note that, although RPL is
   an IP routing protocol, it is not deployed on the general Internet;
   it is limited to specific, contained networks.

   This should be considered anomalous and is not a model for future
   ICMP message types.  That is, ICMP is not intended as a transport for
   other protocols and SHOULD NOT be used in that way in future
   specifications.  In particular, while it is adequate to use ICMP as a
   discovery protocol, it does not extend to full routing capabilities.

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2.2.  Applications Using ICMP

   Some applications make use of ICMP error notifications, or even
   deliberately create anomalous conditions in order to elicit ICMP
   messages.  These ICMP messages are then used to generate feedback to
   the higher layer.  Some of these applications include some of the
   most widespread examples, such as PING, TRACEROUTE, and Path MTU
   Discovery (PMTUD).  These uses are considered acceptable because they
   use existing ICMP message types and do not change ICMP functionality.

2.3.  Extending ICMP

   ICMP multi-part messages are specified in [RFC4884] by defining an
   extension mechanism for selected ICMP messages.  This mechanism
   addresses a fundamental problem in ICMP extensibility.  An ICMP
   multi-part message carries all of the information that ICMP messages
   carried previously, as well as additional information that
   applications may require.

   Some currently defined ICMP extensions include ICMP extensions for
   Multiprotocol Label Switching [RFC4950] and ICMP extensions for
   interface and next-hop identification [RFC5837].

   Extensions to ICMP SHOULD follow the requirements provided in

2.4.  ICMPv4 vs. ICMPv6

   Because ICMPv6 is used for IPv6 Neighbor Discovery, deployed IPv6
   routers, IPv6-capable security gateways, and IPv6-capable firewalls
   normally support administrator configuration of how specific ICMPv6
   message types are handled.  By contrast, deployed IPv4 routers,
   IPv4-capable security gateways, and IPv4-capable firewalls are less
   likely to allow an administrator to configure how specific ICMPv4
   message types are handled.  So, at present, ICMPv6 messages usually
   have a higher probability of travelling end-to-end than ICMPv4

3.  ICMP's Role in the Internet

   ICMP was originally intended to be a mechanism for gateways or
   destination hosts to report error conditions back to source hosts in
   ICMPv4 [RFC0792]; ICMPv6 [RFC4443] is modeled after it.  ICMP is also
   used to perform IP-layer functions, such as diagnostics (e.g., PING).

   ICMP is defined to be an integral part of IP and must be implemented
   by every IP module.  This is true for ICMPv4 as an integral part of
   IPv4 (see the Introduction of [RFC0792]), and for ICMPv6 as an

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   integral part of IPv6 (see Section 2 of [RFC4443]).  When first
   defined, ICMP messages were thought of as IP messages that didn't
   carry any higher-layer data.  It could be conjectured that the term
   "control" was used because ICMP messages were not "data" messages.

   The word "control" in the protocol name did not describe ICMP's
   function (i.e., it did not "control" the Internet); rather, it was
   used to communicate about the control functions in the Internet.  For
   example, even though ICMP included a redirect message type that
   affects routing behavior in the context of a LAN segment, it was not
   and is not used as a generic routing protocol.

4.  Security Considerations

   This document describes a high-level policy for adding ICMP types and
   codes.  While special attention must be paid to the security
   implications of any particular new ICMP type or code, this
   recommendation presents no new security considerations.

   From a security perspective, ICMP plays a part in the Photuris
   protocol [RFC2521].  But more generally, ICMP is not a secure
   protocol and does not include features to be used to discover network
   security parameters or to report on network security anomalies in the
   forwarding plane.

   Additionally, new ICMP functionality (e.g., ICMP extensions, or new
   ICMP types or codes) needs to consider potential ways that ICMP can
   be abused (e.g., Smurf IP DoS [CA-1998-01]).

5.  Acknowledgments

   This document was originally proposed by, and received substantial
   review and suggestions from, Ron Bonica.  Discussions with Pascal
   Thubert helped clarify the history of RPL's use of ICMP.  We are very
   grateful for the review, feedback, and comments from Ran Atkinson,
   Tim Chown, Joe Clarke, Adrian Farrel, Ray Hunter, Hilarie Orman, Eric
   Rosen, JINMEI Tatuya, and Wen Zhang, which resulted in a much
   improved document.

6.  References

6.1.  Normative references

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

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

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   [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.

   [RFC4884]  Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
              "Extended ICMP to Support Multi-Part Messages", RFC 4884,
              April 2007.

6.2.  Informative references

              CERT, "Smurf IP Denial-of-Service Attacks", CERT Advisory
              CA-1998-01, January 1998,

              "IP Diagnostics Technical Interest Group", ,

   [RFC2521]  Karn, P. and W. Simpson, "ICMP Security Failures
              Messages", RFC 2521, March 1999.

   [RFC2780]  Bradner, S. and V. Paxson, "IANA Allocation Guidelines For
              Values In the Internet Protocol and Related Headers", BCP
              37, RFC 2780, March 2000.

   [RFC4950]  Bonica, R., Gan, D., Tappan, D., and C. Pignataro, "ICMP
              Extensions for Multiprotocol Label Switching", RFC 4950,
              August 2007.

   [RFC5837]  Atlas, A., Bonica, R., Pignataro, C., Shen, N., and JR.
              Rivers, "Extending ICMP for Interface and Next-Hop
              Identification", RFC 5837, April 2010.

   [RFC6550]  Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R.,
              Levis, P., Pister, K., Struik, R., Vasseur, JP., and R.
              Alexander, "RPL: IPv6 Routing Protocol for Low-Power and
              Lossy Networks", RFC 6550, March 2012.

   [RFC6918]  Gont, F. and C. Pignataro, "Formally Deprecating Some
              ICMPv4 Message Types", RFC 6918, April 2013.

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Authors' Addresses

   Melinda Shore
   No Mountain Software
   PO Box 16271
   Two Rivers, AK  99716

   Phone: +1 907 322 9522
   EMail: melinda.shore@nomountain.net

   Carlos Pignataro
   Cisco Systems, Inc.
   7200-12 Kit Creek Road
   Research Triangle Park, NC  27709

   EMail: cpignata@cisco.com

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