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 (C) 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).
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.
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.
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.
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]):
(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).
(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.
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.
(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.
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.
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