Network Working Group A. Conta, Digital Equipment Corporation Request for Comments: 1885 S. Deering, Xerox PARC Category: Standards Track December 1995
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.
Abstract
This document specifies a set of Internet Control Message Protocol (ICMP) messages for use with version 6 of the Internet Protocol (IPv6). The Internet Group Management Protocol (IGMP) messages specified in STD 5, RFC 1112 have been merged into ICMP, for IPv6, and are included in this document.
The Internet Protocol, version 6 (IPv6) is a new version of IP. IPv6 uses the Internet Control Message Protocol (ICMP) as defined for IPv4 [RFC-792], with a number of changes. The Internet Group Membership Protocol (IGMP) specified for IPv4 [RFC-1112] has also been revised and has been absorbed into ICMP for IPv6. 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 or multicast group membership maintenance; such procedures are described in other documents (e.g., [RFC-1112, RFC-1191]). 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.
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") and multicast membership reporting. ICMPv6 is an integral part of IPv6 and MUST be fully implemented by every IPv6 node.
2.1 Message General Format
ICMPv6 messages are grouped into two classes: error messages and informational messages. Error messages are identified as such by having 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:
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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)
ICMPv6 informational messages:
128 Echo Request (see section 4.1) 129 Echo Reply (see section 4.2) 130 Group Membership Query (see section 4.3) 131 Group Membership Report (see section 4.3) 132 Group Membership Reduction (see section 4.3)
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. (NOTE: this is different than the value used to identify ICMP for IPv4.)
The ICMPv6 messages have the following general format:
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.
2.2 Message Source Address Determination
A node that sends 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:
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(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 a multicast or anycast group in which the node is a member, the Source Address of the reply must be a unicast address belonging to the interface on which the multicast or anycast packet was received.
(c) If the message is a response to a message sent to an address that does not belong to the node, the Source Address should be that unicast address belonging to the node that will be most helpful in diagnosing the error. For example, if the message is a response to a packet forwarding action that cannot complete successfully, the Source Address should be a unicast address belonging to the interface on which the packet forwarding failed.
(d) Otherwise, the node's routing table must be examined to determine which interface will be used to transmit the message to its destination, and a unicast address belonging to that interface must be used as the Source Address of the message.
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, 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. (NOTE: 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 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, it MUST be passed to the upper layer.
(b) If an ICMPv6 informational message of unknown type is received, it MUST be silently discarded.
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(c) Every ICMPv6 error message (type < 128) includes as much of the IPv6 offending (invoking) packet (the packet that caused the error) as will fit without making the error message packet exceed 576 octets.
(d) In those cases where the internet-layer protocol is required to pass an ICMPv6 error message to the upper-layer protocol, 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 protocol entity to handle the error.
If the original packet had an unusually large amount of extension headers, it is possible that the upper-layer protocol type may not be present in the ICMPv6 message, due to truncation of the original packet to meet the 576-octet limit. In that case, the error message is silently dropped after any IPv6-layer processing.
(e) An ICMPv6 error message MUST NOT be sent as a result of receiving:
(e.1) an ICMPv6 error message, or
(e.2) 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 that has the Option Type highest-order two bits set to 10), or
(e.3) a packet sent as a link-layer multicast, (the exception from e.2 applies to this case too), or
(e.4) a packet sent as a link-layer broadcast, (the exception from e.2 applies to this case too), or
(e.5) 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 sender to be an IPv6 anycast address.
(f) Finally, to each sender of an erroneous data packet, an IPv6 node MUST limit the rate of ICMPv6 error messages sent, in order to limit the bandwidth and forwarding costs incurred by the error messages when a generator of erroneous packets does not respond to those error messages by ceasing its transmissions.
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There are a variety of ways of implementing the rate-limiting function, for example:
(f.1) Timer-based - for example, limiting the rate of transmission of error messages to a given source, or to any source, to at most once every T milliseconds.
(f.2) Bandwidth-based - for example, limiting the rate at which error messages are sent from a particular interface to some fraction F of the attached link's bandwidth.
The limit parameters (e.g., T or F in the above examples) MUST be configurable for the node, with a conservative default value (e.g., T = 1 second, NOT 0 seconds, or F = 2 percent, NOT 100 percent).
The following sections describe the message formats for the above ICMPv6 messages.
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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 will fit without the ICMPv6 packet + | exceeding 576 octets |
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 - not a neighbor 3 - address unreachable 4 - port unreachable
Unused This field is unused for all code values. It must be initialized to zero by the sender 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 (NOTE: this error can occur only in nodes that do not hold a "default route" in their routing tables).
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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 next destination address in the Routing header is not a neighbor of the processing node but the "strict" bit is set for that address, then the Code field is set to 2.
If there is any other reason for the failure to deliver, e.g., inability to resolve the IPv6 destination address into a corresponding link address, or a link-specific problem of some sort, then the Code field is set to 3.
A destination node SHOULD send 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.
Upper layer notification
A node receiving the ICMPv6 Destination Unreachable message MUST notify the upper-layer protocol.
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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 will fit without the ICMPv6 packet + | exceeding 576 octets |
IPv6 Fields:
Destination Address
Copied from the Source Address field of the invoking packet.
ICMPv6 Fields:
Type 2
Code 0
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 [RFC-1191].
Sending a Packet Too Big Message makes an exception to one of the rules of when to send an ICMPv6 error message, in that unlike other messages, it is sent in response to a packet received with an IPv6 multicast destination address, or 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 protocol.
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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 will fit without the ICMPv6 packet + | exceeding 576 octets |
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 sender and ignored by the receiver.
Description
If a router receives a packet with a Hop Limit of zero, or a router decrements a packet's Hop Limit to zero, it MUST discard the packet and send 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.
The router sending an ICMPv6 Time Exceeded message with Code 0 SHOULD consider the receiving interface of the packet as the interface on which the packet forwarding failed in following rule (d) for selecting the Source Address of the message.
Upper layer notification
An incoming Time Exceeded message MUST be passed to the upper-layer protocol.
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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 will fit without the ICMPv6 packet + | exceeding 576 octets |
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 576-byte limit 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 send an ICMPv6 Parameter Problem message to the packet's source, indicating the type and location of the problem.
The pointer identifies the octet of the original packet's header where the error was detected. For example, an ICMPv6 message with Type field = 4, Code field = 1, and Pointer field = 40 would indicate
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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 protocol.
Identifier An identifier to aid in matching Echo Replies to this Echo Request. May be zero.
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 sends corresponding Echo Replies. A node SHOULD also implement an application-layer interface for sending Echo Requests and receiving Echo Replies, for diagnostic purposes.
Upper layer notification
A node receiving this ICMPv6 message MAY notify the upper-layer protocol.
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.
Sequence The sequence number from the invoking Echo Request Number 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 sends corresponding Echo Replies. A node SHOULD also implement an application-layer interface for sending 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 address. The source address of the reply MUST be a unicast address belonging to the interface on which the multicast Echo Request message was received.
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The data received in the ICMPv6 Echo Request message MUST be returned entirely and unmodified in the ICMPv6 Echo Reply message, unless the Echo Reply would exceed the MTU of the path back to the Echo requester, in which case the data is truncated to fit that path MTU.
Upper layer notification
Echo Reply messages MUST be passed to the ICMPv6 user interface, unless the corresponding Echo Request originated in the IP layer.
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4.3 Group Membership Messages
The ICMPv6 Group Membership Messages have the following format:
In a Group Membership Query message, the multicast address of the group being queried, or the Link-Local All-Nodes multicast address.
In a Group Membership Report or a Group Membership Reduction message, the multicast address of the group being reported or terminated.
Hop Limit 1
ICMPv6 Fields:
Type 130 - Group Membership Query 131 - Group Membership Report 132 - Group Membership Reduction
Code 0
Maximum Response Delay
In Query messages, the maximum time that responding Report messages may be delayed, in milliseconds.
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In Report and Reduction messages, this field is is initialized to zero by the sender and ignored by receivers.
Unused Initialized to zero by the sender; ignored by receivers.
Multicast Address
The address of the multicast group about which the message is being sent. In Query messages, the Multicast Address field may be zero, implying a query for all groups.
Description
The ICMPv6 Group Membership messages are used to convey information about multicast group membership from nodes to their neighboring routers. The details of their usage is given in [RFC-1112].
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5. References
[IPv6] Deering, S., and R. Hinden, "Internet Protocol, Version 6, Specification", RFC 1883, Xerox PARC, Ipsilon Networks, December 1995.
[IPv6-ADDR] Hinden, R., and S. Deering, Editors, "IP Version 6 Addressing Architecture", RFC 1884, Ipsilon Networks, Xerox PARC, December 1995.
[IPv6-DISC] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", Work in Progress.
[RFC-792] Postel, J., "Internet Control Message Protocol", STD 5, RFC 792, USC/Information Sciences Institute, September 1981.
[RFC-1112] Deering, S., "Host Extensions for IP Multicasting", STD 5, RFC 1112, Stanford University, August 1989.
[RFC-1122] Braden, R., "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, USC/Information Sciences Institute, October 1989.
[RFC-1191] Mogul, J., and S. Deering, "Path MTU Discovery", RFC 1191, DECWRL, Stanford University, November 1990.
6. Acknowledgements
The document is derived from previous ICMP drafts 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, and Scott Bradner (in chronological order) provided extensive review information and feedback.
7. Security Considerations
Security issues are not discussed in this memo.
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Authors' Addresses:
Alex Conta Stephen Deering Digital Equipment Corporation Xerox Palo Alto Research Center 110 Spitbrook Rd 3333 Coyote Hill Road Nashua, NH 03062 Palo Alto, CA 94304
