ICMP Use Policy: An Acceptable Use Policy for New ICMP Types and Codes
Guidelines on when it is, and is not, a good idea to add new message types and codes to ICMP.
Shore, M. and C. Pignataro, "An Acceptable Use Policy for New ICMP Types and Codes", BCP 189, RFC 7279, DOI 10.17487/RFC7279, May 2014, <https://www.rfc-editor.org/info/rfc7279>.
@misc{rfc7279,
series = {Request for Comments},
number = 7279,
howpublished = {RFC 7279},
publisher = {RFC Editor},
doi = {10.17487/RFC7279},
url = {https://www.rfc-editor.org/info/rfc7279},
author = {M. Shore and C. Pignataro},
title = {{An Acceptable Use Policy for New ICMP Types and Codes}},
pagetotal = 10,
year = 2014,
month = may,
} RFC text
Contents
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
Abstract
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
http://www.rfc-editor.org/info/rfc7279.
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.
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.
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
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
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
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.
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
[CA-1998-01]
CERT, "Smurf IP Denial-of-Service Attacks", CERT Advisory
CA-1998-01, January 1998,
<http://www.cert.org/advisories/CA-1998-01.html>.
[DIAGNOSTICS]
"IP Diagnostics Technical Interest Group", ,
<https://svn.tools.ietf.org/area/ops/trac/wiki/
TIG_DIAGNOSTICS>.
[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
US
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
US
EMail: cpignata@cisco.com
AI ELI5
On this page
§1Why a Policy Was Needed
There was concern about a lack of clarity around when new message types and codes should be added to ICMP, including ICMPv4 (RFC 792) and ICMPv6 (RFC 4443). This document lays out a policy on when, and when not, to move functionality into ICMP.
It came out of discussions among ICMP experts in the IP Diagnostics Technical Interest Group of the Operations and Management (OPS) area, and from concerns expressed by the OPS area leadership.
It does not replace RFC 2780, which covers the process for allocating values in the IANA registries. This RFC is about the policy applied in the standards process, not the allocation process.
People were not sure when it was okay to add new kinds of messages to ICMP. So some experts wrote down the rules of the road.
§2The Acceptable Use Policy
Any future message types added to ICMP should be limited to two broad categories.
- Informing a datagram's originator that a forwarding plane anomaly was encountered downstream. The originator must be able to tell from the ICMP message whether or not the datagram was discarded.
- Discovering and conveying dynamic information about a node (other than information usually carried in routing protocols), discovering and conveying network-specific parameters, and discovering on-link routers and hosts.
Normally, ICMP SHOULD NOT be used to implement a general-purpose routing or network management protocol. It does have a role in conveying dynamic information about a network, which falls in the second category.
ICMP may be used for two jobs: telling a sender that its mail hit a problem on the way, and asking neighbors who is nearby and what they are like. It should not be used to run the whole post office.
- Forwarding plane anomaliesTell a datagram's originator that something went wrong downstream, and whether the datagram was discarded.
- Dynamic information and discoveryConvey node or network parameters, and discover on-link routers and hosts.
- Not allowedA general-purpose routing or network management protocol (SHOULD NOT).
§3Existing Message Types and Applications
The RFC sorts existing message types into four groups: IPv4 forwarding plane anomaly reporting, IPv4 router or host discovery, IPv6 forwarding plane anomaly reporting and IPv6 router or host discovery. For example, IPv4 types 3 (Destination Unreachable), 11 (Time Exceeded) and 12 (Parameter Problem) are anomaly reports, while types 8 (Echo) and 9 (Router Advertisement) are discovery. In IPv6, types 1 to 4 are anomaly reports (including 2, Packet Too Big), and types such as 128 (Echo Request), 133 to 136 (router and neighbor messages) and 155 (RPL Control Message) are in the discovery group. Several IPv4 types are marked Deprecated, and RFC 6918 formally deprecated some of them.
Some applications use ICMP error notifications, or deliberately create anomalous conditions to elicit ICMP messages, and turn them into feedback for the higher layer. PING, TRACEROUTE and Path MTU Discovery (PMTUD) are the examples given. These uses are acceptable because they use existing ICMP message types and do not change ICMP functionality.
The RFC makes two piles of existing messages: problem reports and who-is-there questions. Tools like ping and traceroute are fine because they use the existing notes in a new way and do not change what the notes mean.
§4Routing, RPL and Extending ICMP
ICMP is an integral part of the IP layer. It is not a routing protocol or a transport for routing information. The RFC lists characteristics that make it a poor choice for one: it is frequently filtered, it is not authenticated, and it is easily spoofed. Specialist hardware processing of ICMP would also disrupt the deployment of an ICMP-based routing or management protocol.
RPL, the IPv6 routing protocol for low-power and lossy networks (RFC 6550), uses ICMP as a transport. The RFC treats this as an exception that is anomalous and not a model for future types. RPL is not deployed on the general Internet and is limited to specific, contained networks. Using ICMP as a discovery protocol is adequate, but it does not extend to full routing capabilities.
For extending ICMP, multi-part messages are specified in RFC 4884, and extensions to ICMP SHOULD follow its requirements. Existing extensions include those for MPLS (RFC 4950) and for interface and next-hop identification (RFC 5837).
ICMP notes can be lost, forged and are often blocked, so they are a bad way to run a delivery route map. One special network type does it anyway, but that is an odd case that others should not copy.
§5ICMPv4 versus ICMPv6 and ICMP's Role
Because ICMPv6 is used for IPv6 Neighbor Discovery, deployed IPv6 routers, security gateways and firewalls normally let administrators configure how specific ICMPv6 message types are handled. Deployed IPv4 equipment is less likely to allow this. So, at the time of writing, ICMPv6 messages usually have a higher probability of travelling end-to-end than ICMPv4 messages.
ICMP was originally meant as a way for gateways or destination hosts to report error conditions to source hosts, and ICMPv6 is modeled after ICMPv4. It is also used for IP-layer functions such as diagnostics. ICMP is defined as an integral part of IP and must be implemented by every IP module. The word "control" in the name describes communication about the Internet's control functions, not control of the Internet. Even though ICMP has a redirect message that affects routing behavior on a LAN segment, it was not and is not used as a generic routing protocol.
The newer version of ICMP gets through firewalls more often than the old one. Despite its name, ICMP does not steer the Internet. It only passes notes about how things are going.
§6Security Considerations
The RFC is a high-level policy and presents no new security considerations. Any particular new ICMP type or code still needs special attention to its security implications.
ICMP is not a secure protocol and has no features to discover network security parameters or to report network security anomalies in the forwarding plane. It plays a part in the Photuris protocol (RFC 2521). New ICMP functionality also needs to consider how ICMP can be abused, with the Smurf IP DoS attack given as an example.
ICMP has no lock on it, so anyone who adds a new kind of note has to think about how bad people might misuse it.