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IETF RFC 4443
Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification
Last modified on Friday, March 17th, 2006
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Network Working Group A. Conta
Request for Comments: 4443 Transwitch
Obsoletes: 2463 S. Deering
Updates: 2780 Cisco Systems
Category: Standards Track M. Gupta, Ed.
Tropos Networks
March 2006
Internet Control Message Protocol (ICMPv6)
for the Internet Protocol Version 6 (IPv6) Specification
 Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright © The Internet Society (2006).
Abstract
This document describes the format of a set of control messages used
in ICMPv6 (Internet Control Message Protocol). ICMPv6 is the
Internet Control Message Protocol for Internet Protocol version 6
(IPv6).
Conta, et al. Standards Track PAGE 1 
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
Table of Contents
1. Introduction ....................................................2
2. ICMPv6 (ICMP for IPv6) ..........................................3
2.1. Message General Format .....................................3
2.2. Message Source Address Determination .......................5
2.3. Message Checksum Calculation ...............................5
2.4. Message Processing Rules ...................................5
3. ICMPv6 Error Messages ...........................................8
3.1. Destination Unreachable Message ............................8
3.2. Packet Too Big Message ....................................10
3.3. Time Exceeded Message .....................................11
3.4. Parameter Problem Message .................................12
4. ICMPv6 Informational Messages ..................................13
4.1. Echo Request Message ......................................13
4.2. Echo Reply Message ........................................14
5. Security Considerations ........................................15
5.1. Authentication and Confidentiality of ICMP Messages .......15
5.2. ICMP Attacks ..............................................16
6. IANA Considerations ............................................17
6.1. Procedure for New ICMPV6 Type and Code Value Assignments ..17
6.2. Assignments for This Document .............................18
7. References .....................................................19
7.1. Normative References ......................................19
7.2. Informative References ....................................19
8. Acknowledgements ...............................................20
Appendix A - Changes since RFC 2463................................21
1. Introduction
The Internet Protocol version 6 (IPv6) uses the Internet Control
Message Protocol (ICMP) as defined for IPv4 [RFC 792], with a number
of changes. The resulting protocol is called ICMPv6 and has an IPv6
Next Header value of 58.
This document describes the format of a set of control messages used
in ICMPv6. It does not describe the procedures for using these
messages to achieve functions like Path MTU discovery; these
procedures are described in other documents (e.g., [PMTU]). Other
documents may also introduce additional ICMPv6 message types, such as
Neighbor Discovery messages [IPv6-DISC], subject to the general rules
for ICMPv6 messages given in Section 2 of this document.
Terminology defined in the IPv6 specification [IPv6] and the IPv6
Routing and Addressing specification [IPv6-ADDR] applies to this
document as well.
Conta, et al. Standards Track PAGE 2
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
This document obsoletes RFC 2463 [RFC 2463] and updates RFC 2780
[RFC 2780].
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].
2. ICMPv6 (ICMP for IPv6)
ICMPv6 is used by IPv6 nodes to report errors encountered in
processing packets, and to perform other internet-layer functions,
such as diagnostics (ICMPv6 "ping"). ICMPv6 is an integral part of
IPv6, and the base protocol (all the messages and behavior required
by this specification) MUST be fully implemented by every IPv6 node.
2.1. Message General Format
Every ICMPv6 message is preceded by an IPv6 header and zero or more
IPv6 extension headers. The ICMPv6 header is identified by a Next
Header value of 58 in the immediately preceding header. (This is
different from the value used to identify ICMP for IPv4.)
The ICMPv6 messages have the following general format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Message Body +
| |
The type field indicates the type of the message. Its value
determines the format of the remaining data.
The code field depends on the message type. It is used to create an
additional level of message granularity.
The checksum field is used to detect data corruption in the ICMPv6
message and parts of the IPv6 header.
ICMPv6 messages are grouped into two classes: error messages and
informational messages. Error messages are identified as such by a
zero in the high-order bit of their message Type field values. Thus,
error messages have message types from 0 to 127; informational
messages have message types from 128 to 255.
Conta, et al. Standards Track PAGE 3
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
This document defines the message formats for the following ICMPv6
messages:
ICMPv6 error messages:
1 Destination Unreachable (see Section 3.1)
2 Packet Too Big (see Section 3.2)
3 Time Exceeded (see Section 3.3)
4 Parameter Problem (see Section 3.4)
100 Private experimentation
101 Private experimentation
127 Reserved for expansion of ICMPv6 error messages
ICMPv6 informational messages:
128 Echo Request (see Section 4.1)
129 Echo Reply (see Section 4.2)
200 Private experimentation
201 Private experimentation
255 Reserved for expansion of ICMPv6 informational messages
Type values 100, 101, 200, and 201 are reserved for private
experimentation. They are not intended for general use. It is
expected that multiple concurrent experiments will be done with the
same type values. Any wide-scale and/or uncontrolled usage should
obtain real allocations as defined in Section 6.
Type values 127 and 255 are reserved for future expansion of the type
value range if there is a shortage in the future. The details of
this are left for future work. One possible way of doing this that
would not cause any problems with current implementations is that if
the type equals 127 or 255, the code field should be used for the new
assignment. Existing implementations would ignore the new
assignments as specified in Section 2.4, (b). The new messages using
these expanded type values could assign fields in the message body
for its code values.
Sections 3 and 4 describe the message formats for the ICMPv6 error
message types 1 through 4 and informational message types 128 and
129.
Conta, et al. Standards Track PAGE 4
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
Inclusion of, at least, the start of the invoking packet is intended
to allow the originator of a packet that has resulted in an ICMPv6
error message to identify the upper-layer protocol and process that
sent the packet.
2.2. Message Source Address Determination
A node that originates an ICMPv6 message has to determine both the
Source and Destination IPv6 Addresses in the IPv6 header before
calculating the checksum. If the node has more than one unicast
address, it MUST choose the Source Address of the message as follows:
(a) If the message is a response to a message sent to one of the
node's unicast addresses, the Source Address of the reply MUST be
that same address.
(b) If the message is a response to a message sent to any other
address, such as
- a multicast group address,
- an anycast address implemented by the node, or
- a unicast address that does not belong to the node
the Source Address of the ICMPv6 packet MUST be a unicast address
belonging to the node. The address SHOULD be chosen according to
the rules that would be used to select the source address for any
other packet originated by the node, given the destination address
of the packet. However, it MAY be selected in an alternative way
if this would lead to a more informative choice of address
reachable from the destination of the ICMPv6 packet.
2.3. Message Checksum Calculation
The checksum is the 16-bit one's complement of the one's complement
sum of the entire ICMPv6 message, starting with the ICMPv6 message
type field, and prepended with a "pseudo-header" of IPv6 header
fields, as specified in [IPv6, Section 8.1]. The Next Header value
used in the pseudo-header is 58. (The inclusion of a pseudo-header
in the ICMPv6 checksum is a change from IPv4; see [IPv6] for the
rationale for this change.)
For computing the checksum, the checksum field is first set to zero.
2.4. Message Processing Rules
Implementations MUST observe the following rules when processing
ICMPv6 messages (from [RFC 1122]):
Conta, et al. Standards Track PAGE 5
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
(a) If an ICMPv6 error message of unknown type is received at its
destination, it MUST be passed to the upper-layer process that
originated the packet that caused the error, where this can be
identified (see Section 2.4, (d)).
(b) If an ICMPv6 informational message of unknown type is received,
it MUST be silently discarded.
(c) Every ICMPv6 error message (type < 128) MUST include as much of
the IPv6 offending (invoking) packet (the packet that caused the
error) as possible without making the error message packet exceed
the minimum IPv6 MTU [IPv6].
(d) In cases where the internet-layer protocol is required to pass an
ICMPv6 error message to the upper-layer process, the upper-layer
protocol type is extracted from the original packet (contained in
the body of the ICMPv6 error message) and used to select the
appropriate upper-layer process to handle the error.
In cases where it is not possible to retrieve the upper-layer
protocol type from the ICMPv6 message, the ICMPv6 message is
silently dropped after any IPv6-layer processing. One example of
such a case is an ICMPv6 message with an unusually large amount
of extension headers that does not have the upper-layer protocol
type due to truncation of the original packet to meet the minimum
IPv6 MTU [IPv6] limit. Another example is an ICMPv6 message with
an ESP extension header for which it is not possible to decrypt
the original packet due to either truncation or the
unavailability of the state necessary to decrypt the packet.
(e) An ICMPv6 error message MUST NOT be originated as a result of
receiving the following:
(e.1) An ICMPv6 error message.
(e.2) An ICMPv6 redirect message [IPv6-DISC].
(e.3) A packet destined to an IPv6 multicast address. (There are
two exceptions to this rule: (1) the Packet Too Big Message
(Section 3.2) to allow Path MTU discovery to work for IPv6
multicast, and (2) the Parameter Problem Message, Code 2
(Section 3.4) reporting an unrecognized IPv6 option (see
Section 4.2 of [IPv6]) that has the Option Type highest-
order two bits set to 10).
(e.4) A packet sent as a link-layer multicast (the exceptions
from e.3 apply to this case, too).
Conta, et al. Standards Track PAGE 6
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
(e.5) A packet sent as a link-layer broadcast (the exceptions
from e.3 apply to this case, too).
(e.6) A packet whose source address does not uniquely identify a
single node -- e.g., the IPv6 Unspecified Address, an IPv6
multicast address, or an address known by the ICMP message
originator to be an IPv6 anycast address.
(f) Finally, in order to limit the bandwidth and forwarding costs
incurred by originating ICMPv6 error messages, an IPv6 node MUST
limit the rate of ICMPv6 error messages it originates. This
situation may occur when a source sending a stream of erroneous
packets fails to heed the resulting ICMPv6 error messages.
Rate-limiting of forwarded ICMP messages is out of scope of this
specification.
A recommended method for implementing the rate-limiting function
is a token bucket, limiting the average rate of transmission to
N, where N can be either packets/second or a fraction of the
attached link's bandwidth, but allowing up to B error messages to
be transmitted in a burst, as long as the long-term average is
not exceeded.
Rate-limiting mechanisms that cannot cope with bursty traffic
(e.g., traceroute) are not recommended; for example, a simple
timer-based implementation, allowing an error message every T
milliseconds (even with low values for T), is not reasonable.
The rate-limiting parameters SHOULD be configurable. In the case
of a token-bucket implementation, the best defaults depend on
where the implementation is expected to be deployed (e.g., a
high-end router vs. an embedded host). For example, in a
small/mid-size device, the possible defaults could be B=10,
N=10/s.
NOTE: THE RESTRICTIONS UNDER (e) AND (f) ABOVE TAKE PRECEDENCE OVER
ANY REQUIREMENT ELSEWHERE IN THIS DOCUMENT FOR ORIGINATING ICMP ERROR
MESSAGES.
The following sections describe the message formats for the above
ICMPv6 messages.
Conta, et al. Standards Track PAGE 7
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
3. ICMPv6 Error Messages
3.1. Destination Unreachable Message
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unused |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| As much of invoking packet |
+ as possible without the ICMPv6 packet +
| exceeding the minimum IPv6 MTU [IPv6] |
IPv6 Fields:
Destination Address
Copied from the Source Address field of the invoking
packet.
ICMPv6 Fields:
Type 1
Code 0 - No route to destination
1 - Communication with destination
administratively prohibited
2 - Beyond scope of source address
3 - Address unreachable
4 - Port unreachable
5 - Source address failed ingress/egress policy
6 - Reject route to destination
Unused This field is unused for all code values.
It must be initialized to zero by the originator
and ignored by the receiver.
Description
A Destination Unreachable message SHOULD be generated by a router, or
by the IPv6 layer in the originating node, in response to a packet
that cannot be delivered to its destination address for reasons other
than congestion. (An ICMPv6 message MUST NOT be generated if a
packet is dropped due to congestion.)
If the reason for the failure to deliver is lack of a matching entry
in the forwarding node's routing table, the Code field is set to 0.
Conta, et al. Standards Track PAGE 8
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
(This error can occur only in nodes that do not hold a "default
route" in their routing tables.)
If the reason for the failure to deliver is administrative
prohibition (e.g., a "firewall filter"), the Code field is set to 1.
If the reason for the failure to deliver is that the destination is
beyond the scope of the source address, the Code field is set to 2.
This condition can occur only when the scope of the source address is
smaller than the scope of the destination address (e.g., when a
packet has a link-local source address and a global-scope destination
address) and the packet cannot be delivered to the destination
without leaving the scope of the source address.
If the reason for the failure to deliver cannot be mapped to any of
other codes, the Code field is set to 3. Example of such cases are
an inability to resolve the IPv6 destination address into a
corresponding link address, or a link-specific problem of some sort.
One specific case in which a Destination Unreachable message is sent
with a code 3 is in response to a packet received by a router from a
point-to-point link, destined to an address within a subnet assigned
to that same link (other than one of the receiving router's own
addresses). In such a case, the packet MUST NOT be forwarded back
onto the arrival link.
A destination node SHOULD originate a Destination Unreachable message
with Code 4 in response to a packet for which the transport protocol
(e.g., UDP) has no listener, if that transport protocol has no
alternative means to inform the sender.
If the reason for the failure to deliver is that the packet with this
source address is not allowed due to ingress or egress filtering
policies, the Code field is set to 5.
If the reason for the failure to deliver is that the route to the
destination is a reject route, the Code field is set to 6. This may
occur if the router has been configured to reject all the traffic for
a specific prefix.
Codes 5 and 6 are more informative subsets of code 1.
For security reasons, it is recommended that implementations SHOULD
allow sending of ICMP destination unreachable messages to be
disabled, preferably on a per-interface basis.
Conta, et al. Standards Track PAGE 9
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
Upper Layer Notification
A node receiving the ICMPv6 Destination Unreachable message MUST
notify the upper-layer process if the relevant process can be
identified (see Section 2.4, (d)).
3.2. Packet Too Big Message
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MTU |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| As much of invoking packet |
+ as possible without the ICMPv6 packet +
| exceeding the minimum IPv6 MTU [IPv6] |
IPv6 Fields:
Destination Address
Copied from the Source Address field of the invoking
packet.
ICMPv6 Fields:
Type 2
Code Set to 0 (zero) by the originator and ignored by the
receiver.
MTU The Maximum Transmission Unit of the next-hop link.
Description
A Packet Too Big MUST be sent by a router in response to a packet
that it cannot forward because the packet is larger than the MTU of
the outgoing link. The information in this message is used as part
of the Path MTU Discovery process [PMTU].
Originating a Packet Too Big Message makes an exception to one of the
rules as to when to originate an ICMPv6 error message. Unlike other
messages, it is sent in response to a packet received with an IPv6
multicast destination address, or with a link-layer multicast or
link-layer broadcast address.
Conta, et al. Standards Track PAGE 10
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
Upper Layer Notification
An incoming Packet Too Big message MUST be passed to the upper-layer
process if the relevant process can be identified (see Section 2.4,
(d)).
3.3. Time Exceeded Message
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unused |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| As much of invoking packet |
+ as possible without the ICMPv6 packet +
| exceeding the minimum IPv6 MTU [IPv6] |
IPv6 Fields:
Destination Address
Copied from the Source Address field of the invoking
packet.
ICMPv6 Fields:
Type 3
Code 0 - Hop limit exceeded in transit
1 - Fragment reassembly time exceeded
Unused This field is unused for all code values.
It must be initialized to zero by the originator
and ignored by the receiver.
Description
If a router receives a packet with a Hop Limit of zero, or if a
router decrements a packet's Hop Limit to zero, it MUST discard the
packet and originate an ICMPv6 Time Exceeded message with Code 0 to
the source of the packet. This indicates either a routing loop or
too small an initial Hop Limit value.
An ICMPv6 Time Exceeded message with Code 1 is used to report
fragment reassembly timeout, as specified in [IPv6, Section 4.5].
Conta, et al. Standards Track PAGE 11
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
Upper Layer Notification
An incoming Time Exceeded message MUST be passed to the upper-layer
process if the relevant process can be identified (see Section 2.4,
(d)).
3.4. Parameter Problem Message
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pointer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| As much of invoking packet |
+ as possible without the ICMPv6 packet +
| exceeding the minimum IPv6 MTU [IPv6] |
IPv6 Fields:
Destination Address
Copied from the Source Address field of the invoking
packet.
ICMPv6 Fields:
Type 4
Code 0 - Erroneous header field encountered
1 - Unrecognized Next Header type encountered
2 - Unrecognized IPv6 option encountered
Pointer Identifies the octet offset within the
invoking packet where the error was detected.
The pointer will point beyond the end of the ICMPv6
packet if the field in error is beyond what can fit
in the maximum size of an ICMPv6 error message.
Description
If an IPv6 node processing a packet finds a problem with a field in
the IPv6 header or extension headers such that it cannot complete
processing the packet, it MUST discard the packet and SHOULD
originate an ICMPv6 Parameter Problem message to the packet's source,
indicating the type and location of the problem.
Conta, et al. Standards Track PAGE 12
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
Codes 1 and 2 are more informative subsets of Code 0.
The pointer identifies the octet of the original packet's header
where the error was detected. For example, an ICMPv6 message with a
Type field of 4, Code field of 1, and Pointer field of 40 would
indicate that the IPv6 extension header following the IPv6 header of
the original packet holds an unrecognized Next Header field value.
Upper Layer Notification
A node receiving this ICMPv6 message MUST notify the upper-layer
process if the relevant process can be identified (see Section 2.4,
(d)).
4. ICMPv6 Informational Messages
4.1. Echo Request Message
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data ...
+-+-+-+-+-
IPv6 Fields:
Destination Address
Any legal IPv6 address.
ICMPv6 Fields:
Type 128
Code 0
Identifier An identifier to aid in matching Echo Replies
to this Echo Request. May be zero.
Conta, et al. Standards Track PAGE 13
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
Sequence Number
A sequence number to aid in matching Echo Replies
to this Echo Request. May be zero.
Data Zero or more octets of arbitrary data.
Description
Every node MUST implement an ICMPv6 Echo responder function that
receives Echo Requests and originates corresponding Echo Replies. A
node SHOULD also implement an application-layer interface for
originating Echo Requests and receiving Echo Replies, for diagnostic
purposes.
Upper Layer Notification
Echo Request messages MAY be passed to processes receiving ICMP
messages.
4.2. Echo Reply Message
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data ...
+-+-+-+-+-
IPv6 Fields:
Destination Address
Copied from the Source Address field of the invoking
Echo Request packet.
ICMPv6 Fields:
Type 129
Code 0
Identifier The identifier from the invoking Echo Request message.
Conta, et al. Standards Track PAGE 14
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
Sequence Number
The sequence number from the invoking Echo Request
message.
Data The data from the invoking Echo Request message.
Description
Every node MUST implement an ICMPv6 Echo responder function that
receives Echo Requests and originates corresponding Echo Replies. A
node SHOULD also implement an application-layer interface for
originating Echo Requests and receiving Echo Replies, for diagnostic
purposes.
The source address of an Echo Reply sent in response to a unicast
Echo Request message MUST be the same as the destination address of
that Echo Request message.
An Echo Reply SHOULD be sent in response to an Echo Request message
sent to an IPv6 multicast or anycast address. In this case, the
source address of the reply MUST be a unicast address belonging to
the interface on which the Echo Request message was received.
The data received in the ICMPv6 Echo Request message MUST be returned
entirely and unmodified in the ICMPv6 Echo Reply message.
Upper Layer Notification
Echo Reply messages MUST be passed to the process that originated an
Echo Request message. An Echo Reply message MAY be passed to
processes that did not originate the Echo Request message.
Note that there is no limitation on the amount of data that can be
put in Echo Request and Echo Reply Messages.
5. Security Considerations
5.1. Authentication and Confidentiality of ICMP Messages
ICMP protocol packet exchanges can be authenticated using the IP
Authentication Header [IPv6-AUTH] or IP Encapsulating Security
Payload Header [IPv6-ESP]. Confidentiality for the ICMP protocol
packet exchanges can be achieved using the IP Encapsulating Security
Payload Header [IPv6-ESP].
[SEC-ARCH] describes the IPsec handling of ICMP traffic in detail.
Conta, et al. Standards Track PAGE 15
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
5.2. ICMP Attacks
ICMP messages may be subject to various attacks. A complete
discussion can be found in the IP Security Architecture [IPv6-SA]. A
brief discussion of these attacks and their prevention follows:
1. ICMP messages may be subject to actions intended to cause the
receiver to believe the message came from a different source from
that of the message originator. The protection against this
attack can be achieved by applying the IPv6 Authentication
mechanism [IPv6-AUTH] to the ICMP message.
2. ICMP messages may be subject to actions intended to cause the
message or the reply to it to go to a destination different from
that of the message originator's intention. The protection
against this attack can be achieved by using the Authentication
Header [IPv6-AUTH] or the Encapsulating Security Payload Header
[IPv6-ESP]. The Authentication Header provides the protection
against change for the source and the destination address of the
IP packet. The Encapsulating Security Payload Header does not
provide this protection, but the ICMP checksum calculation
includes the source and the destination addresses, and the
Encapsulating Security Payload Header protects the checksum.
Therefore, the combination of ICMP checksum and the Encapsulating
Security Payload Header provides protection against this attack.
The protection provided by the Encapsulating Security Payload
Header will not be as strong as the protection provided by the
Authentication Header.
3. ICMP messages may be subject to changes in the message fields, or
payload. The authentication [IPv6-AUTH] or encryption [IPv6-ESP]
of the ICMP message protects against such actions.
4. ICMP messages may be used to attempt denial-of-service attacks by
sending back to back erroneous IP packets. An implementation that
correctly followed Section 2.4, paragraph (f), of this
specification, would be protected by the ICMP error rate limiting
mechanism.
5. The exception number 2 of rule e.3 in Section 2.4 gives a
malicious node the opportunity to cause a denial-of-service attack
to a multicast source. A malicious node can send a multicast
packet with an unknown destination option marked as mandatory,
with the IPv6 source address of a valid multicast source. A large
number of destination nodes will send an ICMP Parameter Problem
Message to the multicast source, causing a denial-of-service
attack. The way multicast traffic is forwarded by the multicast
routers requires that the malicious node be part of the correct
Conta, et al. Standards Track PAGE 16
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
multicast path, i.e., near to the multicast source. This attack
can only be avoided by securing the multicast traffic. The
multicast source should be careful while sending multicast traffic
with the destination options marked as mandatory, because they can
cause a denial-of-service attack to themselves if the destination
option is unknown to a large number of destinations.
6. As the ICMP messages are passed to the upper-layer processes, it
is possible to perform attacks on the upper layer protocols (e.g.,
TCP) with ICMP [TCP-attack]. It is recommended that the upper
layers perform some form of validation of ICMP messages (using the
information contained in the payload of the ICMP message) before
acting upon them. The actual validation checks are specific to
the upper layers and are out of the scope of this specification.
Protecting the upper layer with IPsec mitigates these attacks.
ICMP error messages signal network error conditions that were
encountered while processing an internet datagram. Depending on
the particular scenario, the error conditions being reported might
or might not get solved in the near term. Therefore, reaction to
ICMP error messages may depend not only on the error type and code
but also on other factors, such as the time at which the error
messages are received, previous knowledge of the network error
conditions being reported, and knowledge of the network scenario
in which the receiving host is operating.
6. IANA Considerations
6.1. Procedure for New ICMPV6 Type and Code Value Assignments
The IPv6 ICMP header defined in this document contains the following
fields that carry values assigned from IANA-managed name spaces: Type
and Code. Code field values are defined relative to a specific Type
value.
Values for the IPv6 ICMP Type fields are allocated using the
following procedure:
1. The IANA should allocate and permanently register new ICMPv6 type
codes from IETF RFC publication. This is for all RFC types,
including standards track, informational, and experimental status,
that originate from the IETF and have been approved by the IESG
for publication.
2. IETF working groups with working group consensus and area director
approval can request reclaimable ICMPV6 type code assignments from
the IANA. The IANA will tag the values as "reclaimable in
future".
Conta, et al. Standards Track PAGE 17
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
The "reclaimable in the future" tag will be removed when an RFC is
published that documents the protocol as defined in 1. This will
make the assignment permanent and update the reference on the IANA
web pages.
At the point where the ICMPv6 type values are 85% assigned, the
IETF will review the assignments tagged "reclaimable in the
future" and inform the IANA which ones should be reclaimed and
reassigned.
3. Requests for new ICMPv6 type value assignments from outside the
IETF are only made through the publication of an IETF document,
per 1 above. Note also that documents published as "RFC Editor
contributions" [RFC 3978] are not considered IETF documents.
The assignment of new Code values for the Type values defined in this
document require standards action or IESG approval. The policy for
assigning Code values for new IPv6 ICMP Types not defined in this
document should be defined in the document defining the new Type
values.
6.2. Assignments for This Document
The following has updated assignments located at:
http://www.iana.org/assignments/icmpv6-parameters
The IANA has reassigned ICMPv6 type 1 "Destination Unreachable" code
2, which was unassigned in [RFC 2463], to:
2 - Beyond scope of source address
The IANA has assigned the following two new codes values for ICMPv6
type 1 "Destination Unreachable":
5 - Source address failed ingress/egress policy
6 - Reject route to destination
The IANA has assigned the following new type values:
100 Private experimentation
101 Private experimentation
127 Reserved for expansion of ICMPv6 error messages
200 Private experimentation
201 Private experimentation
Conta, et al. Standards Track PAGE 18
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
255 Reserved for expansion of ICMPv6 informational messages
7. References
7.1. Normative References
[IPv6] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[IPv6-DISC] Narten, T., Nordmark, E., and W. Simpson, "Neighbor
Discovery for IP Version 6 (IPv6)", RFC 2461, December
1998.
[RFC 792] Postel, J., "Internet Control Message Protocol", STD 5,
RFC 792, September 1981.
[RFC 2463] Conta, A. and S. Deering, "Internet Control Message
Protocol (ICMPv6) for the Internet Protocol Version 6
(IPv6) Specification", RFC 2463, December 1998.
[RFC 1122] Braden, R., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122, October 1989.
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 3978] Bradner, S., "IETF Rights in Contributions", BCP 78, RFC
3978, March 2005.
7.2. Informative References
[RFC 2780] Bradner, S. and V. Paxson, "IANA Allocation Guidelines
For Values In the Internet Protocol and Related
Headers", BCP 37, RFC 2780, March 2000.
[IPv6-ADDR] Hinden, R. and S. Deering, "Intpernet Protocol Version 6
(IPv6) Addressing Architecture", RFC 3513, April 2003.
[PMTU] McCann, J., Deering, S., and J. Mogul, "Path MTU
Discovery for IP version 6", RFC 1981, August 1996.
[IPv6-SA] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
[IPv6-AUTH] Kent, S., "IP Authentication Header", RFC 4302, December
2005.
Conta, et al. Standards Track PAGE 19
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
[IPv6-ESP] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
4203, December 2005.
[SEC-ARCH] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[TCP-attack] Gont, F., "ICMP attacks against TCP", Work in Progress.
8. Acknowledgements
The document is derived from previous ICMP documents of the SIPP and
IPng working group.
The IPng working group, and particularly Robert Elz, Jim Bound, Bill
Simpson, Thomas Narten, Charlie Lynn, Bill Fink, Scott Bradner,
Dimitri Haskin, Bob Hinden, Jun-ichiro Itojun Hagino, Tatuya Jinmei,
Brian Zill, Pekka Savola, Fred Templin, and Elwyn Davies (in
chronological order) provided extensive review information and
feedback.
Bob Hinden was the document editor for this document.
Conta, et al. Standards Track PAGE 20
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
Appendix A - Changes since RFC 2463
The following changes were made from RFC 2463:
- Edited the Abstract to make it a little more elaborate.
- Corrected typos in Section 2.4, where references to sub-bullet e.2
were supposed to be references to e.3.
- Removed the Timer-based and the Bandwidth-based methods from the
example rate-limiting mechanism for ICMP error messages. Added
Token-bucket based method.
- Added specification that all ICMP error messages shall have exactly
32 bits of type-specific data, so that receivers can reliably find
the embedded invoking packet even when they don't recognize the
ICMP message Type.
- In the description of Destination Unreachable messages, Code 3,
added rule prohibiting forwarding of packets back onto point-to-
point links from which they were received, if their destination
addresses belong to the link itself ("anti-ping-ponging" rule).
- Added description of Time Exceeded Code 1 (fragment reassembly
timeout).
- Added "beyond scope of source address", "source address failed
ingress/egress policy", and "reject route to destination" messages
to the family of "unreachable destination" type ICMP error messages
(Section 3.1).
- Reserved some ICMP type values for experimentation.
- Added a NOTE in Section 2.4 that specifies ICMP message processing
rules precedence.
- Added ICMP REDIRECT to the list in Section 2.4, (e) of cases in
which ICMP error messages are not to be generated.
- Made minor editorial changes in Section 2.3 on checksum
calculation, and in Section 5.2.
- Clarified in Section 4.2, regarding the Echo Reply Message; the
source address of an Echo Reply to an anycast Echo Request should
be a unicast address, as in the case of multicast.
Conta, et al. Standards Track PAGE 21
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
- Revised the Security Considerations section. Added the use of the
Encapsulating Security Payload Header for authentication. Changed
the requirement of an option of "not allowing unauthenticated ICMP
messages" to MAY from SHOULD.
- Added a new attack in the list of possible ICMP attacks in Section
5.2.
- Separated References into Normative and Informative.
- Added reference to RFC 2780 "IANA Allocation Guidelines For Values
In the Internet Protocol and Related Headers". Also added a note
that this document updates RFC 2780.
- Added a procedure for new ICMPv6 Type and Code value assignments in
the IANA Considerations section.
- Replaced word "send" with "originate" to make it clear that ICMP
packets being forwarded are out of scope of this specification.
- Changed the ESP and AH references to the updated ESP and AH
documents.
- Added reference to the updated IPsec Security Architecture
document.
- Added a SHOULD requirement for allowing the sending of ICMP
destination unreachable messages to be disabled.
- Simplified the source address selection of the ICMPv6 packet.
- Reorganized the General Message Format (Section 2.1).
- Removed the general packet format from Section 2.1. It refers to
Sections 3 and 4 for packet formats now.
- Added text about attacks to the transport protocols that could
potentially be caused by ICMP.
Conta, et al. Standards Track PAGE 22
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
Authors' Addresses
Alex Conta
Transwitch Corporation
3 Enterprise Drive
Shelton, CT 06484
USA
EMail: aconta@txc.com
Stephen Deering
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134-1706
USA
Mukesh Gupta, Ed.
Tropos Networks
555 Del Rey Avenue
Sunnyvale, CA 94085
Phone: +1 408-331-6889
EMail: mukesh.gupta@tropos.com
Conta, et al. Standards Track PAGE 23
RFC 4443 ICMPv6 (ICMP for IPv6) March 2006
Full Copyright Statement
Copyright © The Internet Society (2006).
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 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
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Copies of IPR disclosures made to the IETF Secretariat and any
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The IETF invites any interested party to bring to its attention any
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Acknowledgement
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Administrative Support Activity (IASA).
Conta, et al. Standards Track PAGE 24
Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification
RFC TOTAL SIZE: 48969 bytes
PUBLICATION DATE: Friday, March 17th, 2006
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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