Network Working Group M. Shore
Internet-Draft No Mountain Software
Intended status: BCP C. Pignataro
Expires: June 8, 2014 Cisco Systems, Inc.
December 5, 2013
An Acceptable Use Policy for New ICMP Types and Codes
draft-shore-icmp-aup-07
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 Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on June 8, 2014.
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Acceptable use policy . . . . . . . . . . . . . . . . . . . . . 3
2.1. Classification of existing message types . . . . . . . . . 3
2.1.1. A few notes on RPL . . . . . . . . . . . . . . . . . . 5
2.2. Extending ICMP . . . . . . . . . . . . . . . . . . . . . . 6
2.3. ICMPv4 vs. ICMPv6 . . . . . . . . . . . . . . . . . . . . . 6
3. ICMP's role in the internet . . . . . . . . . . . . . . . . . . 6
4. Management vs. control . . . . . . . . . . . . . . . . . . . . 7
5. Security considerations . . . . . . . . . . . . . . . . . . . . 8
6. IANA considerations . . . . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8
8. Informative references . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
There has been some recent concern expressed about a lack of clarity
around when to add new message types and codes to ICMP (including
ICMPv4 [RFC0792] and ICMPv6 [RFC4443]). We attempt to lay out a
description of when (and when not) to move functionality into ICMP.
This document is the result of discussions among ICMP experts within
the OPS area's IP Diagnostics Technical Interest Group [1] 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,
RFC 2780 [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.
2. Acceptable use policy
In this document we describe a proposed acceptable use policy for new
ICMP message types and codes, and provide some background behind the
proposed policy.
In summary, we propose that 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, other uses are not advisable. While ICMP's role is not to
be a general-purpose network management protocol, it does have a role
to play in conveying dynamic information about a network.
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:
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3: Destination unreachable
4: Source quench (deprecated)
5: Redirect
6: Alternate host address (deprecated)
11: Time exceeded
12: Parameter problem
31: Datagram conversion error (deprecated)
32: Mobile host redirect (deprecated)
41: ICMP messages utilized by experimental mobility protocols,
such as Seamoby
IPv4 router or host discovery:
0: Echo reply
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)
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
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4: Parameter problem
137: Redirect message
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
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. A few notes on RPL
RPL, the IPv6 Routing protocol for low-power and lossy networks (see
[RFC6550]) appears to be something of an outlier among the existing
ICMP message types, as the expansion of its acronym appears to be an
actual routing protocol using ICMP for transport.
This should be considered anomalous and is not a model for future
ICMP message types. Our understanding is that the working group
initially defined a discovery protocol extending existing ICMPv6
Neighbor Discovery messages before moving to its own native ICMP
type.
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It is typically the case that routing protocols have transport
requirements that are not met by ICMP. For example, there will be
reliability guarantees and security guarantees that are not provided
by ICMP, forcing protocol developers to design their own mechanisms.
Given the availability of other IETF standard transports for routing,
this reinvention should be avoided.
2.2. 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 [RFC4884].
2.3. 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 routers to report
error conditions back to hosts in ICMPv4 [RFC0792], and ICMPv6
[RFC4443] is modeled after it. The word "control" in the protocol
name did not describe ICMP's function (i.e. it did not "control" the
internet), but rather that 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 and is not used as a generic routing
protocol.
Most likely because of the presence of the word "control" in the
protocol name, ICMP is often understood to be a control protocol,
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borrowing some terminology from circuit networks and the PSTN. That
is probably not correct - it might be more correct to describe it as
being closer to a management plane protocol, given the data plane/
control plane/ management plane taxonomy often used in describing
telephony protocols. However, layering in IP networks is not very
clean and there's often some intermingling of function that can tend
to lead to confusion about where to place new functions.
In following sections we provide some background on the differences
between control and management traffic.
4. Management vs. control
In this section we attempt to draw a distinction between management
and control planes, acknowledging in advance that this may serve to
muddle the differences even further. Ultimately the difference may
not matter that much for the purpose of creating a policy for adding
new types to ICMP, but because the terminology of "management and
control planes" has become ubiquitous, even in IETF discussions, and
because it has come up in prior discussions of ICMP policies, it
seems worthwhile to take a few paragraph to describe what management
and control plane are and what they are not.
The terms "management plane" and "control plane" came into use to
describe one aspect of layering in telecommunications networks.
"Management plane" is described in [I-D.ietf-opsawg-oam-overview],
and "control plane" is defined in [RFC6192].
It is particularly important, in the context of this discussion, to
understand that "control plane" in telecommunications networks almost
always refers to 'signaling,' or call control and network control
information. This includes "call" establishment and teardown, route
establishment and teardown, requesting QoS or other parameters, and
other similar artifacts.
"Management," on the other hand, involves an exchange between a
management application and managed entities such as network nodes,
and includes "inline management" and "management" per se. Typical
"inline management" functions include fault management and
performance monitoring (Service Level Agreement (SLA) compliance),
discovery, and typical "management" include protocols such as SNMP
and NETCONF.
The correct answer to the question of where ICMP fits into the
management/control/data taxonomy is that it doesn't, at least not
neatly. While some of the message types are unambiguously management
messages, at least within the narrow confines of a management/control
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dichotomy (ICMP type 3, or "unreachable" messages), others are less
clearly identifiable. For example, the "redirect" (ICMP type 5)
message can be construed to contain control (in this case, routing)
information, even though it is in some very real sense an error
message.
At this time,
o there are plethora of other protocols that can be (and are) used
for control traffic, whether they're routing protocols, telephony
signaling protocols, QoS protocols, middlebox protocols, AAA
protocols, etc.
o the transport characteristics needed by control traffic can be
incompatible with the ICMP protocol standard -- for example, they
may require reliable delivery, very large payloads, or have
security requirements that cannot be met.
and because of this we propose that any future message types added to
ICMP should conform to the policy proposed in Section 2. ICMP should
not be used as a routing or network management protocol.
5. Security considerations
This document attempts to describe 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. 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.
6. IANA considerations
There are no actions required by IANA.
7. 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
grateful for feedback from Joe Clarke and Wen Zhang.
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8. Informative references
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, September 1981.
[RFC2780] Bradner, S. and V. Paxson, "IANA Allocation Guidelines For
Values In the Internet Protocol and Related Headers",
BCP 37, RFC 2780, March 2000.
[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.
[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.
[RFC4884] Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
"Extended ICMP to Support Multi-Part Messages", RFC 4884,
April 2007.
[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.
[RFC6192] Dugal, D., Pignataro, C., and R. Dunn, "Protecting the
Router Control Plane", RFC 6192, March 2011.
[I-D.ietf-opsawg-oam-overview]
Mizrahi, T., Sprecher, N., Bellagamba, E., and Y.
Weingarten, "An Overview of Operations, Administration,
and Maintenance (OAM) Data Plane Tools",
draft-ietf-opsawg-oam-overview-10 (work in progress),
October 2013.
[1] <https://svn.tools.ietf.org/area/ops/trac/wiki/TIG_DIAGNOSTICS>
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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
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