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

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 leadership.

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", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 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 policy.

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.
  1. 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 publication.

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
      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 [RFC6918].

IPv6 forwarding plane anomaly reporting:

      1:   Destination Unreachable
      2:   Packet Too Big
      3:   Time Exceeded
      4:   Parameter Problem


ICMP messages utilized by experimental mobility protocols such as Seamoby

IPv6 router or host discovery:


           Echo Request


           Echo Reply


           Multicast Listener Query


           Multicast Listener Report


           Multicast Listener Done


           Router Solicitation


           Router Advertisement


           Neighbor Solicitation


           Neighbor Advertisement


           Redirect Message


           Router Renumbering


ICMP Node Information Query


ICMP Node Information Response


Inverse Neighbor Discovery Solicitation Message


Inverse Neighbor Discovery Advertisement Message


Version 2 Multicast Listener Report


Home Agent Address Discovery Request Message


Home Agent Address Discovery Reply Message


           Mobile Prefix Solicitation


           Mobile Prefix Advertisement


Certification Path Solicitation Message


Certification Path Advertisement Message


ICMP messages utilized by experimental mobility protocols such as Seamoby


           Multicast Router Advertisement


           Multicast Router Solicitation


           Multicast Router Termination


           FMIPv6 Messages


           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.

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 [RFC4884].

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 messages.

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 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.
   [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.

Authors' Addresses

   Melinda Shore
   No Mountain Software
   PO Box 16271
   Two Rivers, AK  99716
   Phone: +1 907 322 9522
   Carlos Pignataro
   Cisco Systems, Inc.
   7200-12 Kit Creek Road
   Research Triangle Park, NC  27709