Operational Security Capabilities F. Gont
for IP Network Infrastructure G. Gont
(opsec) UTN/FRH
Internet-Draft March 30, 2008
Intended status: Informational
Expires: October 1, 2008
Recommendations for filtering ICMP messages
draft-gont-opsec-icmp-filtering-00.txt
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on October 1, 2008.
Abstract
This document document provides advice on the filtering of ICMPv4 and
ICMPv6 messages. Additionaly, it discusses the operational and
interoperability implications of such filtering.
Gont & Gont Expires October 1, 2008 [Page 1]
Internet-Draft ICMP Filtering March 2008
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Internet Control Message Protocol version 4 (ICMP) . . . . . . 5
2.1. ICMPv4 error messages . . . . . . . . . . . . . . . . . . 5
2.1.1. Destination Unreachable (Type 3) . . . . . . . . . . . 6
2.1.1.1. Net Unreachable (code 0) . . . . . . . . . . . . . 6
2.1.1.2. Host Unreachable (code 1) . . . . . . . . . . . . 7
2.1.1.3. Protocol Unreachable (code 2) . . . . . . . . . . 7
2.1.1.4. Port Unreachable (code 3) . . . . . . . . . . . . 8
2.1.1.5. Fragmentation needed and DF set (code 4) . . . . . 8
2.1.1.6. Source Route Failed (code 5) . . . . . . . . . . . 9
2.1.1.7. Destination network unknown (code 6)
(Deprecated) . . . . . . . . . . . . . . . . . . . 9
2.1.1.8. Destination host unknown (code 7) . . . . . . . . 10
2.1.1.9. Source host isolated (code 8) (Deprecated) . . . . 11
2.1.1.10. Communication with destination network
administratively prohibited (code 9) -
Deprecated . . . . . . . . . . . . . . . . . . . . 11
2.1.1.11. Communication with destination host
administratively prohibited (code 10) -
Deprecated . . . . . . . . . . . . . . . . . . . . 12
2.1.1.12. Network unreachable for type of service (code
11) . . . . . . . . . . . . . . . . . . . . . . . 12
2.1.1.13. Host unreachable for type of service (code 12) . . 13
2.1.1.14. Communication Administratively Prohibited
(code 13) . . . . . . . . . . . . . . . . . . . . 13
2.1.1.15. Host Precedence Violation (code 14) . . . . . . . 14
2.1.1.16. Precedence cutoff in effect (code 15) . . . . . . 14
2.1.2. Source Quench (Type 4, Code 0) . . . . . . . . . . . . 15
2.1.2.1. Message specification . . . . . . . . . . . . . . 15
2.1.2.2. Uses . . . . . . . . . . . . . . . . . . . . . . . 15
2.1.2.3. Threats . . . . . . . . . . . . . . . . . . . . . 16
2.1.2.4. Operational/interoperability impact if blocked . . 16
2.1.3. Redirect (Type 5) . . . . . . . . . . . . . . . . . . 16
2.1.3.1. Redirect datagrams for the Network (code 0) . . . 16
2.1.3.2. Redirect datagrams for the Host (code 1) . . . . . 16
2.1.3.3. Redirect datagrams for the Type of Service and
Network (code 2) . . . . . . . . . . . . . . . . . 17
2.1.3.4. Redirect datagrams for the Type of Service and
Host (code 3) . . . . . . . . . . . . . . . . . . 17
2.1.4. Time exceeded (Type 11) . . . . . . . . . . . . . . . 17
2.1.4.1. Time to live exceeded in transit (code 0) . . . . 17
2.1.4.2. fragment reassembly time exceeded (code 1) . . . . 18
2.1.5. Parameter Problem (Type 12) . . . . . . . . . . . . . 18
2.1.5.1. Pointer indicates the error (code 0) . . . . . . . 19
2.1.5.2. Required option is missing (code 1) . . . . . . . 19
2.2. ICMPv4 Informational messages . . . . . . . . . . . . . . 19
Gont & Gont Expires October 1, 2008 [Page 2]
Internet-Draft ICMP Filtering March 2008
2.2.1. Echo or Echo Reply Message . . . . . . . . . . . . . . 19
2.2.1.1. Echo message (type 8, code 0) . . . . . . . . . . 19
2.2.1.2. Echo reply message (Type 0, code 0) . . . . . . . 20
2.2.2. Router Solicitation or Router Advertisement message . 21
2.2.2.1. Router Solicitation message (type 10, code 0) . . 21
2.2.2.2. Router Advertisement message (type 9, code 0) . . 22
2.2.3. Timestamp or Timestamp Reply Message . . . . . . . . . 22
2.2.3.1. Timestamp message (type 13, code 0) . . . . . . . 22
2.2.3.2. Timestamp reply message (type 14, code 0) . . . . 23
2.2.4. Information Request or Information Reply Message
(Deprecated) . . . . . . . . . . . . . . . . . . . . . 23
2.2.4.1. Information request message (type 15, code 0) . . 23
2.2.4.2. Information reply message (type 16, code 0) . . . 24
2.2.5. Address Mask Request or Address Mask Reply . . . . . . 24
2.2.5.1. Address Mask Request (type 17, code 0) . . . . . . 24
2.2.5.2. Address Mask Reply (type 18, code 0) . . . . . . . 25
3. Internet Control Message Protocol version 6 (ICMPv6) . . . . . 25
3.1. ICMPv6 error messages . . . . . . . . . . . . . . . . . . 25
3.1.1. Destination Unreachable (Type 1) . . . . . . . . . . . 25
3.1.1.1. No route to destination (code 0) . . . . . . . . . 25
3.1.1.2. Communication with destination
administratively prohibited (code 1) . . . . . . . 26
3.1.1.3. Beyond scope of source address (code 2) . . . . . 26
3.1.1.4. Address unreachable (code 3) . . . . . . . . . . . 27
3.1.1.5. Port unreachable (code 4) . . . . . . . . . . . . 27
3.1.1.6. Source address failed ingress/egress policy
(code 5) . . . . . . . . . . . . . . . . . . . . . 27
3.1.1.7. Reject route to destination (code 6) . . . . . . . 28
3.1.2. Packet Too Big Message (Type 2, code 0) . . . . . . . 28
3.1.2.1. Message specification . . . . . . . . . . . . . . 28
3.1.2.2. Uses . . . . . . . . . . . . . . . . . . . . . . . 28
3.1.2.3. Threats . . . . . . . . . . . . . . . . . . . . . 28
3.1.2.4. Operational/interoperability impact if blocked . . 28
3.1.3. Time Exceeded Message (Type 3) . . . . . . . . . . . . 29
3.1.3.1. Hop limit exceeded in transit (code 0) . . . . . . 29
3.1.3.2. Fragment reassembly time exceeded (code 1) . . . . 29
3.1.4. Parameter Problem Message (Type 4) . . . . . . . . . . 29
3.1.4.1. Erroneous header field encountered (code 0) . . . 29
3.1.4.2. Unrecognized Next Header type encountered
(code 1) . . . . . . . . . . . . . . . . . . . . . 30
3.1.4.3. Unrecognized IPv6 option encountered (code 2) . . 30
3.1.5. Private experimentation (Type 100) . . . . . . . . . . 30
3.1.5.1. Message specification . . . . . . . . . . . . . . 30
3.1.5.2. Uses . . . . . . . . . . . . . . . . . . . . . . . 31
3.1.5.3. Threats . . . . . . . . . . . . . . . . . . . . . 31
3.1.5.4. Operational/interoperability impact if blocked . . 31
3.1.6. Private experimentation (Type 101) . . . . . . . . . . 31
3.1.6.1. Message specification . . . . . . . . . . . . . . 31
Gont & Gont Expires October 1, 2008 [Page 3]
Internet-Draft ICMP Filtering March 2008
3.1.6.2. Uses . . . . . . . . . . . . . . . . . . . . . . . 31
3.1.6.3. Threats . . . . . . . . . . . . . . . . . . . . . 31
3.1.6.4. Operational/interoperability impact if blocked . . 31
3.1.7. Reserved for expansion of ICMPv6 error messages
(Type 127) . . . . . . . . . . . . . . . . . . . . . . 31
3.1.7.1. Message specification . . . . . . . . . . . . . . 31
3.1.7.2. Uses . . . . . . . . . . . . . . . . . . . . . . . 31
3.1.7.3. Threats . . . . . . . . . . . . . . . . . . . . . 31
3.1.7.4. Operational/interoperability impact if blocked . . 31
3.2. ICMPv6 Informational messages . . . . . . . . . . . . . . 31
3.2.1. Echo Request or Echo Reply Message . . . . . . . . . . 31
3.2.1.1. Echo Request message (type 128, code 0) . . . . . 31
3.2.1.2. Echo reply message (Type 129, code 0) . . . . . . 32
3.2.2. Private experimentation (Type 200) . . . . . . . . . . 32
3.2.2.1. Message specification . . . . . . . . . . . . . . 32
3.2.2.2. Uses . . . . . . . . . . . . . . . . . . . . . . . 32
3.2.2.3. Threats . . . . . . . . . . . . . . . . . . . . . 32
3.2.2.4. Operational/interoperability impact if blocked . . 32
3.2.3. Private experimentation (Type 201) . . . . . . . . . . 32
3.2.3.1. Message specification . . . . . . . . . . . . . . 32
3.2.3.2. Uses . . . . . . . . . . . . . . . . . . . . . . . 32
3.2.3.3. Threats . . . . . . . . . . . . . . . . . . . . . 33
3.2.3.4. Operational/interoperability impact if blocked . . 33
3.2.4. Reserved for expansion of ICMPv6 informational
messages (Type 255) . . . . . . . . . . . . . . . . . 33
3.2.4.1. Message specification . . . . . . . . . . . . . . 33
3.2.4.2. Uses . . . . . . . . . . . . . . . . . . . . . . . 33
3.2.4.3. Threats . . . . . . . . . . . . . . . . . . . . . 33
3.2.4.4. Operational/interoperability impact if blocked . . 33
4. Security Considerations . . . . . . . . . . . . . . . . . . . 33
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 33
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33
6.1. Normative References . . . . . . . . . . . . . . . . . . . 33
6.2. Informative References . . . . . . . . . . . . . . . . . . 34
Appendix A. Change log (to be removed before publication of
the document as an RFC) . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35
Intellectual Property and Copyright Statements . . . . . . . . . . 36
Gont & Gont Expires October 1, 2008 [Page 4]
Internet-Draft ICMP Filtering March 2008
1. Introduction
This document document provides advice on the filtering of ICMPv4 and
ICMPv6 messages. Additionaly, it discusses the operational and
interoperability implications of such filtering.
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 RFC 2119 [RFC2119].
2. Internet Control Message Protocol version 4 (ICMP)
2.1. ICMPv4 error messages
[RFC0792] is the base specification for the Internet Control Message
Protocol (ICMP) to be used with the Internet Protocol version 4
(IPv4). It defines, among other things, a number of error messages
that can be used by end-systems and intermediate systems to report
errors to the sending system. The Host Requirements RFC [RFC1122]
classifies ICMP error messages into those that indicate "soft
errors", and those that indicate "hard errors", thus roughly defining
the semantics of them.
Section 3.2.2.1 of [RFC1122] specifies the amount of information to
be included in the payload of an ICMP error message, and how ICMP
error messages should be demultiplexed to the corresponding transport
protocol instance. Additionally, it imposes details some scenarios
in which ICMP errors should not be generated.
Section 4.1.3.3 of [RFC1122] states that UDP MUST pass to the
application layer all ICMP error messages that it receives from the
IP layer.
Section 4.2.3.9 of [RFC1122] states that TCP MUST act on an ICMP
error message passed up from the IP layer, directing it to the
connection that created the error.
Section 4.3.2 of [RFC1812] contains a number of requirements for the
generation and processing of ICMP error messages, including:
initialization of the TTL of the error message, the amount of data
from the offending packet to be included in the ICMP payload, setting
the IP Source Address of ICMP error messages, setting of the TOS and
Precedence, processing of IP Source Route option in offending
packets, scenarios in which routers MUST NOT send ICMP error
messages, and application of rate-limiting to ICMP error messages.
The ICMP specification [RFC0792] also defines the ICMP Source Quench
Gont & Gont Expires October 1, 2008 [Page 5]
Internet-Draft ICMP Filtering March 2008
message (type 4, code 0), which is meant to provide a mechanism for
flow control and congestion control.
[RFC1191] defines a mechanism called "Path MTU Discovery" (PMTUD),
which makes use of ICMP error messages of type 3 (Destination
Unreachable), code 4 (fragmentation needed and DF bit set) to allow
systems to determine the MTU of an arbitrary internet path.
Appendix D of [RFC4301] provides information about which ICMP error
messages are produced by hosts, intermediate routers, or both.
2.1.1. Destination Unreachable (Type 3)
The ICMP Destination Unreachable message is sent by a router in
response to a packet which it cannot forward because the destination
(or next hop) is unreachable or a service is unavailable. Examples
of such cases include a message addressed to a host which is not
there and therefore does not respond to ARP requests, and messages
addressed to network prefixes for which the router has no valid
route. [RFC1812] states that a router MUST be able to generate ICMP
Destination Unreachable messages and SHOULD choose a response code
that most closely matches the reason the message is being generated.
Section 3.2.2.1 of [RFC1122] states that a Destination Unreachable
message that is received MUST be reported to the transport layer, and
that the transport layer SHOULD use the information appropriately.
2.1.1.1. Net Unreachable (code 0)
2.1.1.1.1. Message specification
Defined in [RFC0792]. Section 4.3.3.1 of [RFC1812] states that if a
router cannot forward a packet because it has no routes at all
(including no default route) to the destination specified in the
packet, then the router MUST generate a Destination Unreachable, Code
0 (Network Unreachable) ICMP message. Section 3.2.2.1 of [RFC1122]
states that this message may result from a routing transient, and
MUST therefore be interpreted as only a hint, not proof, that the
specified destination is unreachable. For example, it MUST NOT be
used as proof of a dead gateway. Section 4.2.3.9 of [RFC1122] states
that this message indicates a soft error, and therefore TCP MUST NOT
abort the connection, and SHOULD make the information available to
the application.
2.1.1.1.2. Uses
Gont & Gont Expires October 1, 2008 [Page 6]
Internet-Draft ICMP Filtering March 2008
2.1.1.1.3. Threats
2.1.1.1.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts
that could have been avoided by those systems aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
2.1.1.2. Host Unreachable (code 1)
2.1.1.2.1. Message specification
Defined in [RFC0792]. Section 3.2.2.1 of [RFC1122] states that his
message may result from a routing transient, and MUST therefore be
interpreted as only a hint, not proof, that the specified destination
is unreachable. For example, it MUST NOT be used as proof of a dead
gateway. Section 4.2.3.9 of [RFC1122] states that this message
indicates a soft error, and therefore TCP MUST NOT abort the
connection, and SHOULD make the information available to the
application.
2.1.1.2.2. Uses
2.1.1.2.3. Threats
2.1.1.2.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts
that could have been avoided by those systems aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
2.1.1.3. Protocol Unreachable (code 2)
2.1.1.3.1. Message specification
Defined in [RFC0792]. [RFC1122] states that a host SHOULD send a
protocol unreachable when the designated transport protocol is not
supported. Section 4.2.3.9 of [RFC1122] states that this message
indicates a hard error condition, so TCP SHOULD abort the connection.
2.1.1.3.2. Uses
Gont & Gont Expires October 1, 2008 [Page 7]
Internet-Draft ICMP Filtering March 2008
2.1.1.3.3. Threats
2.1.1.3.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts
that could have been avoided by those systems aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
2.1.1.4. Port Unreachable (code 3)
2.1.1.4.1. Message specification
Defined in [RFC0792]. Section 3.2.2.1 of [RFC1122] states that a
host SHOULD send an ICMP port unreachable when the designated
transport protocol (e.g., UDP) is unable to demultiplex the datagram
but has no protocol mechanism to inform the sender. Additionally, it
states that a transport protocol that has its own mechanism for
notifying the sender that a port is unreachable MUST nevertheless
accept an ICMP Port Unreachable for the same purpose.
Section 4.2.3.9 of [RFC1122] states that this message indicates a
hard error condition, so TCP SHOULD abort the connection.
2.1.1.4.2. Uses
2.1.1.4.3. Threats
2.1.1.4.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
2.1.1.5. Fragmentation needed and DF set (code 4)
2.1.1.5.1. Message specification
Defined in [RFC0792]
2.1.1.5.2. Uses
Used for the Path-MTU Discovery mechanism described in [RFC1191].
Gont & Gont Expires October 1, 2008 [Page 8]
Internet-Draft ICMP Filtering March 2008
2.1.1.5.3. Threats
This error message can be used to perform Denial of Service (DoS)
attacks against transport protocols. [I-D.ietf-tcpm-icmp-attacks]
describes the use of this error message to attack TCP connections.
2.1.1.5.4. Operational/interoperability impact if blocked
Filtering this error message breaks the Path-MTU Discovery mechansim
described in [RFC1191].
2.1.1.6. Source Route Failed (code 5)
2.1.1.6.1. Message specification
Defined in [RFC0792]. Section 3.2.2.1 of [RFC1122] states that his
message may result from a routing transient, and MUST therefore be
interpreted as only a hint, not proof, that the specified destination
is unreachable. For example, it MUST NOT be used as proof of a dead
gateway. Section 4.2.3.9 of [RFC1122] states that this message
indicates a soft error, and therefore TCP MUST NOT abort the
connection, and SHOULD make the information available to the
application.
Section 4.2.3.9 of [RFC1122] states that this message indicates a
hard error condition, so TCP SHOULD abort the connection.
2.1.1.6.2. Uses
Signals errors araising from IPv4 source routes.
2.1.1.6.3. Threats
There shouldn't be any security threats araising from the use of this
error message.
2.1.1.6.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
2.1.1.7. Destination network unknown (code 6) (Deprecated)
Gont & Gont Expires October 1, 2008 [Page 9]
Internet-Draft ICMP Filtering March 2008
2.1.1.7.1. Message specification
Defined in [RFC1122]. [RFC1812] states that this code SHOULD NOT be
generated since it would imply on the part of the router that the
destination network does not exist (net unreachable code 0 SHOULD be
used in place of code 6).
2.1.1.7.2. Uses
Signal unreachability condition to the sending system.
2.1.1.7.3. Threats
There shouldn't be any security threats araising from the use of this
error message.
2.1.1.7.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
2.1.1.8. Destination host unknown (code 7)
2.1.1.8.1. Message specification
Defined in [RFC1122], and is generated only when a router can
determine (from link layer advice) that the destination host does not
exist
2.1.1.8.2. Uses
Signal unreachability condition to the sending system.
2.1.1.8.3. Threats
There shouldn't be any security threats araising from the use of this
error message.
2.1.1.8.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
Gont & Gont Expires October 1, 2008 [Page 10]
Internet-Draft ICMP Filtering March 2008
2.1.1.9. Source host isolated (code 8) (Deprecated)
2.1.1.9.1. Message specification
Defined in [RFC1122]. [RFC1812] states that routers SHOULD NOT
generate this error message, and states that whichever of Codes 0
(Network Unreachable) and 1 (Host Unreachable) is appropriate SHOULD
be used instead.
2.1.1.9.2. Uses
Signal unreachability condition to the sending system.
2.1.1.9.3. Threats
There shouldn't be any security threats araising from the use of this
error message.
2.1.1.9.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors]. However, this error message is
deprecated, and thus system should not depend on it for any purpose.
2.1.1.10. Communication with destination network administratively
prohibited (code 9) - Deprecated
2.1.1.10.1. Message specification
This error code is defined in [RFC1122], and was intended for use by
end-to-end encryption devices used by U.S military agencies.
[RFC1812] deprecates its use, stating that routers SHOULD use the
Code 13 (Communication Administratively Prohibited) if they
administratively filter packets.
2.1.1.10.2. Uses
Signal unreachability condition to the sending system.
2.1.1.10.3. Threats
May reveal filtering policies.
Gont & Gont Expires October 1, 2008 [Page 11]
Internet-Draft ICMP Filtering March 2008
2.1.1.10.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors]. However, this error message is
deprecated, and thus system should not depend on it for any purpose.
2.1.1.11. Communication with destination host administratively
prohibited (code 10) - Deprecated
2.1.1.11.1. Message specification
This error code is defined in [RFC1122], and was intended for use by
end-to-end encryption devices used by U.S military agencies.
[RFC1812] deprecates its use, stating that routers SHOULD use the
Code 13 (Communication Administratively Prohibited) if they
administratively filter packets.
2.1.1.11.2. Uses
Signal unreachability condition to the sending system.
2.1.1.11.3. Threats
May reveal filtering policies.
2.1.1.11.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors]. However, this error message is
deprecated, and thus system should not depend on it for any purpose.
2.1.1.12. Network unreachable for type of service (code 11)
2.1.1.12.1. Message specification
Defined in [RFC1122]. Section 4.3.3.1 of [RFC1812] states that if a
router cannot forward a packet because the TOS specified for the
routes is neither the default TOS (0000) nor the TOS of the packet
that the router is attempting to route, then the router MUST generate
a Destination Unreachable, Code 11 (Network Unreachable for TOS) ICMP
message.
Gont & Gont Expires October 1, 2008 [Page 12]
Internet-Draft ICMP Filtering March 2008
2.1.1.12.2. Uses
Signal unreachability condition to the sending system.
2.1.1.12.3. Threats
May reveal routing policies.
2.1.1.12.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
2.1.1.13. Host unreachable for type of service (code 12)
2.1.1.13.1. Message specification
Defined in [RFC1122]. Section 4.3.3.1 of [RFC1812] states that this
message is sent if a packet is to be forwarded to a host that is on a
network that is directly connected to the router and the router
cannot forward the packet because no route to the destination has a
TOS that is either equal to the TOS requested in the packet or is the
default TOS (0000).
2.1.1.13.2. Uses
Signal unreachability condition to the sending system.
2.1.1.13.3. Threats
May reveal routing policies.
2.1.1.13.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
2.1.1.14. Communication Administratively Prohibited (code 13)
2.1.1.14.1. Message specification
Defined in [RFC1812], and is generated if a router cannot forward a
packet due to administrative filtering.
Gont & Gont Expires October 1, 2008 [Page 13]
Internet-Draft ICMP Filtering March 2008
2.1.1.14.2. Uses
Signal unreachability condition (due to filtering policies) to the
sending system.
2.1.1.14.3. Threats
Given that the semantics of this error message are not accurately
specified, some systems might abort transport connections upon
receipt of this error message. [I-D.ietf-tcpm-icmp-attacks].
2.1.1.14.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
2.1.1.15. Host Precedence Violation (code 14)
2.1.1.15.1. Message specification
Defined in [RFC1812], and is sent by the first hop router to a host
to indicate that a requested precedence is not permitted for the
particular combination of source/destination host or network, upper
layer protocol, and source/destination port
2.1.1.15.2. Uses
Signal unreachability condition to the sending system.
2.1.1.15.3. Threats
May reveal routing policies.
2.1.1.15.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
2.1.1.16. Precedence cutoff in effect (code 15)
2.1.1.16.1. Message specification
Defined in [RFC1812], and is sent when the network operators have
imposed a minimum level of precedence required for operation, and a
Gont & Gont Expires October 1, 2008 [Page 14]
Internet-Draft ICMP Filtering March 2008
datagram was sent with a precedence below this level.
2.1.1.16.2. Uses
2.1.1.16.3. Threats
2.1.1.16.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
2.1.2. Source Quench (Type 4, Code 0)
2.1.2.1. Message specification
The Source Quench message is defined in [RFC0792].
Section 3.2.2.3 of [RFC1122] states that host MAY send a Source
Quench message if it is approaching, or has reached, the point at
which it is forced to discard incoming datagrams due to a shortage of
reassembly buffers or other resources. It also states that if a
Source Quench message is received, the IP layer MUST pass it to the
tansport layer, which SHOULD implement a mechanism for responding to
ICMP Source Quench messages.
Section 4.2.3.9 of the Host Requirements RFC [RFC1122] states that
TCP MUST react to ICMP Source Quench messages by slowing transmission
on the connection, and further further adds that the RECOMMENDED
procedure is to put the corresponding connection in the slow-start
phase of TCP's congestion control algorithm [RFC2581].
Section 4.3.3.3 of the Requirements for IP Version 4 Routers RFC
[RFC1812] notes that research seems to suggest that ICMP Source
Quench is an ineffective (and unfair) antidote for congestion, and
states that routers SHOULD NOT send ICMP Source Quench messages in
response to congestion. A router that does originate Source Quench
messages MUST be able to limit the rate at which they are generated.
Finally, Section 4.3.3.3 of [RFC1812] states that a router MAY ignore
any ICMP Source Quench messages it receives.
2.1.2.2. Uses
Gont & Gont Expires October 1, 2008 [Page 15]
Internet-Draft ICMP Filtering March 2008
2.1.2.3. Threats
2.1.2.4. Operational/interoperability impact if blocked
2.1.3. Redirect (Type 5)
Section 3.2.2.2 of [RFC1122] states that SHOULD NOT send an ICMP
Redirect message, and that a host receiving a Redirect message MUST
update its routing information accordingly, and process the ICMP
redirect according to the rules stated in Section 3.3.1.2 of
[RFC1122]. ICMP redirects that specify a a gateway that is not on
the same connected (sub-) net through which the Redirect arrived, or
that are received from a source other than the first-hop gateway
SHOULD be silently disacarded.
Section 4.3.3.2 of [RFC1812] states that a router MAY ignore ICMP
Redirects when choosing a path for a packet originated by the router
if the router is running a routing protocol or if forwarding is
enabled on the router and on the interface over which the packet is
being sent.
2.1.3.1. Redirect datagrams for the Network (code 0)
2.1.3.1.1. Message specification
Defined in [RFC0792].
2.1.3.1.2. Uses
2.1.3.1.3. Threats
2.1.3.1.4. Operational/interoperability impact if blocked
2.1.3.2. Redirect datagrams for the Host (code 1)
2.1.3.2.1. Message specification
Defined in [RFC0792].
2.1.3.2.2. Uses
2.1.3.2.3. Threats
2.1.3.2.4. Operational/interoperability impact if blocked
Gont & Gont Expires October 1, 2008 [Page 16]
Internet-Draft ICMP Filtering March 2008
2.1.3.3. Redirect datagrams for the Type of Service and Network (code
2)
2.1.3.3.1. Message specification
Defined in [RFC0792].
2.1.3.3.2. Uses
2.1.3.3.3. Threats
2.1.3.3.4. Operational/interoperability impact if blocked
2.1.3.4. Redirect datagrams for the Type of Service and Host (code 3)
2.1.3.4.1. Message specification
Defined in [RFC0792].
2.1.3.4.2. Uses
2.1.3.4.3. Threats
2.1.3.4.4. Operational/interoperability impact if blocked
2.1.4. Time exceeded (Type 11)
Section 3.2.2.4 of [RFC1122] states that an incoming Time Exceeded
message MUST be passed to the transport layer.
Section 4.3.3.4 of [RFC1812] states that when the router receives
(i.e., is destined for the router) a Time Exceeded message, it MUST
comply with [RFC1122].
2.1.4.1. Time to live exceeded in transit (code 0)
2.1.4.1.1. Message specification
Defined in [RFC0792].
[RFC1812] states that a router MUST generate a Time Exceeded message
Code 0 (In Transit) when it discards a packet due to an expired TTL
field. Section 4.2.3.9 of [RFC1122] states that this message should
be handled by TCP in the same way as Destination Unreachable codes 0,
1, 5.
Gont & Gont Expires October 1, 2008 [Page 17]
Internet-Draft ICMP Filtering March 2008
2.1.4.1.2. Uses
Used for the traceroute troubleshooting tool. Signals unreachability
condition due to routing loops.
2.1.4.1.3. Threats
Can be used for network mapping.
2.1.4.1.4. Operational/interoperability impact if blocked
Breaks the traceroute tool. May lead to long delays between
connection establishment attempts or long response times that could
have been avoided by aborting non-synchronized connections in
response to ICMP soft errors [I-D.ietf-tcpm-tcp-soft-errors].
2.1.4.2. fragment reassembly time exceeded (code 1)
2.1.4.2.1. Message specification
Defined in [RFC0792]. [RFC0792] states this message may be sent by a
host reassembling a fragmented datagram if it cannot complete the
reassembly due to missing fragments within its time limit. Section
4.2.3.9 of [RFC1122] states that this message should be handled by
TCP in the same way as Destination Unreachable codes 0, 1, 5.
2.1.4.2.2. Uses
Signals fragment reassembly timeout.
2.1.4.2.3. Threats
May reveal the timeout value used by a system for fragment
reassembly.
2.1.4.2.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
2.1.5. Parameter Problem (Type 12)
Section 3.2.2.5 of [RFC1122] states that a host SHOULD generate
Parameter Problem messages. An incoming Parameter Problem message
MUST be passed to the transport layer, and it MAY be reported to the
user. Section 4.2.3.9 of [RFC1122] states that this message should
Gont & Gont Expires October 1, 2008 [Page 18]
Internet-Draft ICMP Filtering March 2008
be handled by TCP in the same way as Destination Unreachable codes 0,
1, 5.
Section 4.3.3.5 of [RFC1812] states that a router MUST generate a
Parameter Problem message for any error not specifically covered by
another ICMP message. The IP header field or IP option including the
byte indicated by the pointer field MUST be included unchanged in the
IP header returned with this ICMP message. Section 4.3.2 of the same
document defines an exception to this rule.
2.1.5.1. Pointer indicates the error (code 0)
2.1.5.1.1. Message specification
Defined in [RFC0792].
2.1.5.1.2. Uses
2.1.5.1.3. Threats
2.1.5.1.4. Operational/interoperability impact if blocked
2.1.5.2. Required option is missing (code 1)
2.1.5.2.1. Message specification
Defined in Section 3.2.2.5 of [RFC1122]. It was meant to be used in
the military community for a missing security option.
2.1.5.2.2. Uses
2.1.5.2.3. Threats
2.1.5.2.4. Operational/interoperability impact if blocked
2.2. ICMPv4 Informational messages
2.2.1. Echo or Echo Reply Message
2.2.1.1. Echo message (type 8, code 0)
2.2.1.1.1. Message specification
Defined in [RFC0792].
Section 3.2.2.6 of [RFC1122] states that every host MUST implement an
ICMP Echo server function that receives Echo Requests and sends
corresponding Echo Replies. A host SHOULD also implement an
Gont & Gont Expires October 1, 2008 [Page 19]
Internet-Draft ICMP Filtering March 2008
application-layer interface for sending an Echo Request and receiving
an Echo Reply, for diagnostic purposes. Section 3.2.2.6 of [RFC1122]
includes a number of requirements for the processing of ICMP Echo
messages and the generation of the corresponding replies.
Section 4.3.3.6 of [RFC1812] contains a number of requirements with
respect to the generation and processing of ICMP Echo or Echo Reply
messsages, including: maximum ICMP message size all routers are
required to receive, a number of factors that may determine whether a
router responds (or not) to an ICMP Echo message, the implementation
of a user/application-layer interface, and the processing of Record
Route, Timestamp and/or Source Route options that might be present in
an ICMP Echo message.
2.2.1.1.2. Uses
Used by the ping troubleshooting tool.
2.2.1.1.3. Threats
Can be used for network mapping [icmp-scanning]. Has been exploited
to perform Smurf attacks [smurf].
2.2.1.1.4. Operational/interoperability impact if blocked
Filtering this error message will break the ping tool. The best
current practice is to rate-limit this ICMP message.
2.2.1.2. Echo reply message (Type 0, code 0)
2.2.1.2.1. Message specification
Defined in [RFC0792].
Section 3.2.2.6 of [RFC1122] states that every host MUST implement an
ICMP Echo server function that receives Echo Requests and sends
corresponding Echo Replies. A host SHOULD also implement an
application-layer interface for sending an Echo Request and receiving
an Echo Reply, for diagnostic purposes. Section 3.2.2.6 of [RFC1122]
includes a number of requirements for the processing of ICMP Echo
messages and the generation of the corresponding replies.
Section 4.3.3.6 of [RFC1812] contains a number of requirements with
respect to the generation and processing of ICMP Echo or Echo Reply
messsages, including: maximum ICMP message size all routers are
required to receive, a number of factors that may determine whether a
router responds (or not) to an ICMP Echo message, the implementation
of a user/application-layer interface, and the processing of Record
Gont & Gont Expires October 1, 2008 [Page 20]
Internet-Draft ICMP Filtering March 2008
Route, Timestamp and/or Source Route options that might be present in
an ICMP Echo message.
2.2.1.2.2. Uses
Used by the ping troubleshooting tool.
2.2.1.2.3. Threats
Can be used for network mapping [icmp-scanning]. Has been exploited
to perform Smurf attacks [smurf].
2.2.1.2.4. Operational/interoperability impact if blocked
Filtering this error message will break the ping tool. The best
current practice is to rate-limit this ICMP message.
2.2.2. Router Solicitation or Router Advertisement message
2.2.2.1. Router Solicitation message (type 10, code 0)
2.2.2.1.1. Message specification
Defined in [RFC1256]
Section 4.3.3.10 of [RFC1812] states that an IP router MUST support
the router part of the ICMP Router Discovery Protocol on all
connected networks on which the router supports either IP multicast
or IP broadcast addressing. The implementation MUST include all the
configuration variables specified for routers, with the specified
defaults.
2.2.2.1.2. Uses
Used by some systems as form of stateless autoconfiguration, to
solicit routers on a network segment.
2.2.2.1.3. Threats
Can be used for network mapping (e.g., learning about routers on a
network segment.).
2.2.2.1.4. Operational/interoperability impact if blocked
This mesages should ot be routed. Therefore, there is no
operational/interoperability impact if blocked.
Gont & Gont Expires October 1, 2008 [Page 21]
Internet-Draft ICMP Filtering March 2008
2.2.2.2. Router Advertisement message (type 9, code 0)
2.2.2.2.1. Message specification
Defined in [RFC1256]
Section 4.3.3.10 of [RFC1812] states that an IP router MUST support
the router part of the ICMP Router Discovery Protocol on all
connected networks on which the router supports either IP multicast
or IP broadcast addressing. The implementation MUST include all the
configuration variables specified for routers, with the specified
defaults.
2.2.2.2.2. Uses
Used to advertise routers on a network segment.
2.2.2.2.3. Threats
Can be spoofed by an attacker to direct all traffic sent on a network
segment to itself.
2.2.2.2.4. Operational/interoperability impact if blocked
This mesages should ot be routed. Therefore, there is no
operational/interoperability impact if blocked.
2.2.3. Timestamp or Timestamp Reply Message
2.2.3.1. Timestamp message (type 13, code 0)
2.2.3.1.1. Message specification
Defined in [RFC0792].
Section 3.2.2.8 of [RFC1122] states that a host MAY implement
Timestamp and Timestamp Reply. For hosts that implement these
messages, a number of requirements are stated.
2.2.3.1.2. Uses
2.2.3.1.3. Threats
Can be used for network mapping, and device fingerprinting.
Gont & Gont Expires October 1, 2008 [Page 22]
Internet-Draft ICMP Filtering March 2008
2.2.3.1.4. Operational/interoperability impact if blocked
None.
2.2.3.2. Timestamp reply message (type 14, code 0)
2.2.3.2.1. Message specification
Defined in [RFC0792].
2.2.3.2.2. Uses
2.2.3.2.3. Threats
Can be used for network mapping, and device fingerprinting.
2.2.3.2.4. Operational/interoperability impact if blocked
None.
2.2.4. Information Request or Information Reply Message (Deprecated)
These messages are described in [RFC0792] as "a way for a host to
find out the number of the network it is on". Section 3.2.2.7 of
[RFC1122] and Section 4.3.3.7 of [RFC1812] deprecate the use of these
messages.
2.2.4.1. Information request message (type 15, code 0)
2.2.4.1.1. Message specification
Defined in [RFC0792].
These messages are described in [RFC0792] as "a way for a host to
find out the number of the network it is on". Section 3.2.2.7 of
[RFC1122] and Section 4.3.3.7 of [RFC1812] deprecate the use of these
messages.
2.2.4.1.2. Uses
2.2.4.1.3. Threats
2.2.4.1.4. Operational/interoperability impact if blocked
Gont & Gont Expires October 1, 2008 [Page 23]
Internet-Draft ICMP Filtering March 2008
2.2.4.2. Information reply message (type 16, code 0)
2.2.4.2.1. Message specification
Defined in [RFC0792].
These messages are described in [RFC0792] as "a way for a host to
find out the number of the network it is on". Section 3.2.2.7 of
[RFC1122] and Section 4.3.3.7 of [RFC1812] deprecate the use of these
messages.
2.2.4.2.2. Uses
2.2.4.2.3. Threats
2.2.4.2.4. Operational/interoperability impact if blocked
2.2.5. Address Mask Request or Address Mask Reply
2.2.5.1. Address Mask Request (type 17, code 0)
2.2.5.1.1. Message specification
Defined in RFC0950. Section 3.2.2.9 of [RFC1122] includes a number
of requirements regarding the generation and processing of this
message.
Section 3.2.2.9 of [RFC1122] states that a host MAY implement sending
ICMP Address Mask Request(s) and receiving ICMP Address Mask
Reply(s). Section 4.3.3.9 of [RFC1812] states that a router MUST
implement support for receiving ICMP Address Mask Request messages
and responding with ICMP Address Mask Reply messages.
2.2.5.1.2. Uses
Was originally defined as a means for system stateless
autoconfiguration.
2.2.5.1.3. Threats
Can be used for network mapping, and OS fingerprinting.
2.2.5.1.4. Operational/interoperability impact if blocked
None.
Gont & Gont Expires October 1, 2008 [Page 24]
Internet-Draft ICMP Filtering March 2008
2.2.5.2. Address Mask Reply (type 18, code 0)
2.2.5.2.1. Message specification
Defined in RFC0950. Section 3.2.2.9 of [RFC1122] includes a number
of requirements regarding the generation and processing of this
message.
Section 3.2.2.9 of [RFC1122] states that a host MAY implement sending
ICMP Address Mask Request(s) and receiving ICMP Address Mask
Reply(s). Section 4.3.3.9 of [RFC1812] states that a router MUST
implement support for receiving ICMP Address Mask Request messages
and responding with ICMP Address Mask Reply messages.
2.2.5.2.2. Uses
Was originally defined as a means for system stateless
autoconfiguration.
2.2.5.2.3. Threats
Canbe used for network mapping, and OS fingerprinting.
2.2.5.2.4. Operational/interoperability impact if blocked
None.
3. Internet Control Message Protocol version 6 (ICMPv6)
3.1. ICMPv6 error messages
The ICMPv6 specification leaves it up to the implementation the
reaction to ICMP error messages. Therefore, the ICMP attacks
described in [I-D.ietf-tcpm-icmp-attacks] might or might not be
effective.
3.1.1. Destination Unreachable (Type 1)
3.1.1.1. No route to destination (code 0)
3.1.1.1.1. Message specification
Defined in [RFC4443].
Gont & Gont Expires October 1, 2008 [Page 25]
Internet-Draft ICMP Filtering March 2008
3.1.1.1.2. Uses
3.1.1.1.3. Threats
3.1.1.1.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
3.1.1.2. Communication with destination administratively prohibited
(code 1)
3.1.1.2.1. Message specification
Defined in [RFC4443].
3.1.1.2.2. Uses
3.1.1.2.3. Threats
3.1.1.2.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
3.1.1.3. Beyond scope of source address (code 2)
3.1.1.3.1. Message specification
Defined in [RFC4443].
3.1.1.3.2. Uses
3.1.1.3.3. Threats
3.1.1.3.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
Gont & Gont Expires October 1, 2008 [Page 26]
Internet-Draft ICMP Filtering March 2008
3.1.1.4. Address unreachable (code 3)
3.1.1.4.1. Message specification
Defined in [RFC4443].
3.1.1.4.2. Uses
3.1.1.4.3. Threats
3.1.1.4.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
3.1.1.5. Port unreachable (code 4)
3.1.1.5.1. Message specification
Defined in [RFC4443].
3.1.1.5.2. Uses
3.1.1.5.3. Threats
This error message might used to perform Denial of Service (DoS)
attacks against transport protocols. [I-D.ietf-tcpm-icmp-attacks]
describes the use of this error message to attack TCP connections.
3.1.1.5.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
3.1.1.6. Source address failed ingress/egress policy (code 5)
3.1.1.6.1. Message specification
Defined in [RFC4443].
3.1.1.6.2. Uses
Gont & Gont Expires October 1, 2008 [Page 27]
Internet-Draft ICMP Filtering March 2008
3.1.1.6.3. Threats
3.1.1.6.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
3.1.1.7. Reject route to destination (code 6)
3.1.1.7.1. Message specification
Defined in [RFC4443].
3.1.1.7.2. Uses
3.1.1.7.3. Threats
3.1.1.7.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
3.1.2. Packet Too Big Message (Type 2, code 0)
3.1.2.1. Message specification
Defined in [RFC4443].
3.1.2.2. Uses
Used for the Path-MTU discovery mechanism for IPv6 defined in
[RFC1981].
3.1.2.3. Threats
This error message can be used to perform Denial of Service (DoS)
attacks against transport protocols. [I-D.ietf-tcpm-icmp-attacks]
describes the use of this error message to attack TCP connections.
3.1.2.4. Operational/interoperability impact if blocked
Filtering this error message will break the Path-MTU Discovery
mechanism defined in [RFC1981].
Gont & Gont Expires October 1, 2008 [Page 28]
Internet-Draft ICMP Filtering March 2008
3.1.3. Time Exceeded Message (Type 3)
3.1.3.1. Hop limit exceeded in transit (code 0)
3.1.3.1.1. Message specification
Defined in [RFC4443].
3.1.3.1.2. Uses
3.1.3.1.3. Threats
3.1.3.1.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
3.1.3.2. Fragment reassembly time exceeded (code 1)
3.1.3.2.1. Message specification
Defined in [RFC4443].
3.1.3.2.2. Uses
Used to signal a timeout in fragment reassembly.
3.1.3.2.3. Threats
May reveal the timeout value used by a system for fragment
reassembly.
3.1.3.2.4. Operational/interoperability impact if blocked
May lead to long delays between connection establishment attempts or
long response times that could have been avoided by aborting non-
synchronized connections in response to ICMP soft errors
[I-D.ietf-tcpm-tcp-soft-errors].
3.1.4. Parameter Problem Message (Type 4)
3.1.4.1. Erroneous header field encountered (code 0)
Gont & Gont Expires October 1, 2008 [Page 29]
Internet-Draft ICMP Filtering March 2008
3.1.4.1.1. Message specification
Defined in [RFC4443].
3.1.4.1.2. Uses
3.1.4.1.3. Threats
This error message might used to perform Denial of Service (DoS)
attacks against transport protocols. [I-D.ietf-tcpm-icmp-attacks]
describes the use of this error message to attack TCP connections.
3.1.4.1.4. Operational/interoperability impact if blocked
3.1.4.2. Unrecognized Next Header type encountered (code 1)
3.1.4.2.1. Message specification
Defined in [RFC4443].
3.1.4.2.2. Uses
3.1.4.2.3. Threats
This error message might used to perform Denial of Service (DoS)
attacks against transport protocols. [I-D.ietf-tcpm-icmp-attacks]
describes the use of this error message to attack TCP connections.
3.1.4.2.4. Operational/interoperability impact if blocked
3.1.4.3. Unrecognized IPv6 option encountered (code 2)
3.1.4.3.1. Message specification
Defined in [RFC4443].
3.1.4.3.2. Uses
3.1.4.3.3. Threats
3.1.4.3.4. Operational/interoperability impact if blocked
3.1.5. Private experimentation (Type 100)
3.1.5.1. Message specification
Defined in [RFC4443].
Gont & Gont Expires October 1, 2008 [Page 30]
Internet-Draft ICMP Filtering March 2008
3.1.5.2. Uses
3.1.5.3. Threats
3.1.5.4. Operational/interoperability impact if blocked
3.1.6. Private experimentation (Type 101)
3.1.6.1. Message specification
Defined in [RFC4443].
3.1.6.2. Uses
3.1.6.3. Threats
3.1.6.4. Operational/interoperability impact if blocked
3.1.7. Reserved for expansion of ICMPv6 error messages (Type 127)
3.1.7.1. Message specification
Defined in [RFC4443].
3.1.7.2. Uses
3.1.7.3. Threats
3.1.7.4. Operational/interoperability impact if blocked
3.2. ICMPv6 Informational messages
3.2.1. Echo Request or Echo Reply Message
3.2.1.1. Echo Request message (type 128, code 0)
3.2.1.1.1. Message specification
Defined in [RFC4443].
3.2.1.1.2. Uses
Used by the ping tool to test reachability.
3.2.1.1.3. Threats
Can be used for network mapping [icmp-scanning] and for performing
Smurf DoS attacks [smurf].
Gont & Gont Expires October 1, 2008 [Page 31]
Internet-Draft ICMP Filtering March 2008
3.2.1.1.4. Operational/interoperability impact if blocked
Filtering this error message will break the ping tool. The best
current practice is to rate-limit this ICMP message.
3.2.1.2. Echo reply message (Type 129, code 0)
3.2.1.2.1. Message specification
Defined in [RFC4443].
3.2.1.2.2. Uses
Used by the ping tool to test reachability.
3.2.1.2.3. Threats
Can be used for network mapping [icmp-scanning] and for performing
Smurf DoS attacks [smurf].
3.2.1.2.4. Operational/interoperability impact if blocked
Filtering this error message will break the ping tool. The best
current practice is to rate-limit this ICMP message.
3.2.2. Private experimentation (Type 200)
3.2.2.1. Message specification
Defined in [RFC4443].
3.2.2.2. Uses
3.2.2.3. Threats
3.2.2.4. Operational/interoperability impact if blocked
3.2.3. Private experimentation (Type 201)
3.2.3.1. Message specification
Defined in [RFC4443].
3.2.3.2. Uses
Gont & Gont Expires October 1, 2008 [Page 32]
Internet-Draft ICMP Filtering March 2008
3.2.3.3. Threats
3.2.3.4. Operational/interoperability impact if blocked
3.2.4. Reserved for expansion of ICMPv6 informational messages (Type
255)
3.2.4.1. Message specification
Defined in [RFC4443].
3.2.4.2. Uses
3.2.4.3. Threats
3.2.4.4. Operational/interoperability impact if blocked
4. Security Considerations
This document does not introduce any new security implications. It
attempts to help mitigate security threats that rely on ICMP through
packet filtering and rate-limiting.
5. Acknowledgements
This survey of ICMP specifications is based on a yet-to-be-published
internet-draft on ICMP by Fernando Gont and Carlos Pignataro. This
document borrows its structure from the "ICMP filtering" wiki started
by George Jones.
Fernando would like to thank Paula Piedra for her love and support.
6. References
6.1. Normative References
[RFC0792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, September 1981.
[RFC1122] Braden, R., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, October 1989.
[RFC1191] Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
November 1990.
Gont & Gont Expires October 1, 2008 [Page 33]
Internet-Draft ICMP Filtering March 2008
[RFC1256] Deering, S., "ICMP Router Discovery Messages", RFC 1256,
September 1991.
[RFC1812] Baker, F., "Requirements for IP Version 4 Routers",
RFC 1812, June 1995.
[RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery
for IP version 6", RFC 1981, August 1996.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2581] Allman, M., Paxson, V., and W. Stevens, "TCP Congestion
Control", RFC 2581, April 1999.
[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.
6.2. Informative References
[I-D.ietf-tcpm-icmp-attacks]
Gont, F., "ICMP attacks against TCP",
draft-ietf-tcpm-icmp-attacks-03 (work in progress),
March 2008.
[I-D.ietf-tcpm-tcp-soft-errors]
Gont, F., "TCP's Reaction to Soft Errors",
draft-ietf-tcpm-tcp-soft-errors-07 (work in progress),
December 2007.
[icmp-scanning]
Arkin, 0., "ICMP Usage in Scanning: The Complete Know-
How", http://www.sys-security.com/archive/papers/
ICMP_Scanning_v3.0.pdf, 2001.
[smurf] CERT, "CERT Advisory CA-1998-01: Smurf IP Denial-of-
Service Attacks",
http://www.cert.org/advisories/CA-1998-01.html, 1998.
Appendix A. Change log (to be removed before publication of the
document as an RFC)
blah
Gont & Gont Expires October 1, 2008 [Page 34]
Internet-Draft ICMP Filtering March 2008
Authors' Addresses
Fernando Gont
Universidad Tecnologica Nacional / Facultad Regional Haedo
Evaristo Carriego 2644
Haedo, Provincia de Buenos Aires 1706
Argentina
Phone: +54 11 4650 8472
Email: fernando@gont.com.ar
URI: http://www.gont.com.ar
Guillermo Gont
Universidad Tecnologica Nacional / Facultad Regional Haedo
Evaristo Carriego 2644
Haedo, Provincia de Buenos Aires 1706
Argentina
Phone: +54 11 4650 8472
Email: guillermo@gont.com.ar
Gont & Gont Expires October 1, 2008 [Page 35]
Internet-Draft ICMP Filtering March 2008
Full Copyright Statement
Copyright (C) The IETF Trust (2008).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Gont & Gont Expires October 1, 2008 [Page 36]