RFC 2463 - Internet Control Message Protocol (ICMPv6) for the In
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Network Working Group A. Conta Request for Comments: 2463 Lucent Obsoletes: 1885 S. Deering Category: Standards Track Cisco Systems December 1998 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 (1998). All Rights Reserved. Abstract This document specifies a set of Internet Control Message Protocol (ICMP) messages for use with version 6 of the Internet Protocol (IPv6). Table of Contents 1. Introduction........................................2 2. ICMPv6 (ICMP for IPv6)..............................2 2.1 Message General Format.......................2 2.2 Message Source Address Determination.........3 2.3 Message Checksum Calculation.................4 2.4 Message Processing Rules.....................4 3. ICMPv6 Error Messages...............................6 3.1 Destination Unreachable Message..............6 3.2 Packet Too Big Message...................... 8 3.3 Time Exceeded Message....................... 9 3.4 Parameter Problem Message...................10 4. ICMPv6 Informational Messages......................11 4.1 Echo Request Message........................11 4.2 Echo Reply Message..........................12 5. Security Considerations............................13 6. References.........................................14 7. Acknowledgments....................................15 8. Authors' Addresses.................................16 Appendix A - Changes since RFC 1885...................17 Full Copyright Statement..............................18 1. Introduction 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 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; such 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. 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 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: 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) 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: 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. 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: (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. (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 the minimum IPv6 MTU [IPv6]. (d) In those 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. 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 minimum IPv6 MTU [IPv6] 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, in order to limit the bandwidth and forwarding costs incurred sending ICMPv6 error messages, an IPv6 node MUST limit the rate of ICMPv6 error messages it sends. This situation may occur when a source sending a stream of erroneous packets fails to heed the resulting ICMPv6 error messages. 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. 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 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 - (not assigned) 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). If the reason for the failure to deliver is administrative prohibition, e.g., a "firewall filter", the Code field is set to 1. 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 process. 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 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 sender 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]. 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 process. 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 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 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 rules for selecting the Source Address of this message are defined in section 2.2. Upper layer notification An incoming Time Exceeded message MUST be passed to the upper-layer process. 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 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 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 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. 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. 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 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. 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. 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. It may be passed to processes that did not originate the Echo Request message. 5. Security Considerations 5.1 Authentication and Encryption of ICMP messages ICMP protocol packet exchanges can be authenticated using the IP Authentication Header [IPv6-AUTH]. A node SHOULD include an Authentication Header when sending ICMP messages if a security association for use with the IP Authentication Header exists for the destination address. The security associations may have been created through manual configuration or through the operation of some key management protocol. Received Authentication Headers in ICMP packets MUST be verified for correctness and packets with incorrect authentication MUST be ignored and discarded. It SHOULD be possible for the system administrator to configure a node to ignore any ICMP messages that are not authenticated using either the Authentication Header or Encapsulating Security Payload. Such a switch SHOULD default to allowing unauthenticated messages. Confidentiality issues are addressed by the IP Security Architecture and the IP Encapsulating Security Payload documents [IPv6-SA, IPv6- ESP]. 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 such attacks and their prevention is as follows: 1. ICMP messages may be subject to actions intended to cause the receiver believe the message came from a different source than 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 go to a destination different than the message originator's intention. The ICMP checksum calculation provides a protection mechanism against changes by a malicious interceptor in the destination and source address of the IP packet carrying that message, provided the ICMP checksum field is protected against change by authentication [IPv6-Auth] or encryption [IPv6-ESP] of the ICMP message. 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 is a protection against such actions. 4. ICMP messages may be used as attempts to perform denial of service attacks by sending back to back erroneous IP packets. An implementation that correctly followed section 2.4, paragraph (f) of this specifications, would be protected by the ICMP error rate limiting mechanism. 6. References [IPv6] Deering, S. and R. Hinden, "Internet Protocol, Version 6, (IPv6) Specification", RFC 2460, December 1998. [IPv6-ADDR] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 2373, July 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-1122] Braden, R., "Requirements for Internet Hosts - Communication Layers", STD 5, RFC 1122, August 1989. [PMTU] McCann, J., Deering, S. and J. Mogul, "Path MTU Discovery for IP version 6", RFC 1981, August 1996. [RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [IPv6-SA] Kent, S. and R. Atkinson, "Security Architecture for the Internet Protocol", RFC 2401, November 1998. [IPv6-Auth] Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402, November 1998. [IPv6-ESP] Kent, S. and R. Atkinson, "IP Encapsulating Security Protocol (ESP)", RFC 2406, November 1998. 7. Acknowledgments 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, Scott Bradner, Dimitri Haskin, and Bob Hinden (in chronological order) provided extensive review information and feedback. 8. Authors' Addresses Alex Conta Lucent Technologies Inc. 300 Baker Ave, Suite 100 Concord, MA 01742 USA Phone: +1 978 287-2842 EMail: firstname.lastname@example.org Stephen Deering Cisco Systems, Inc. 170 West Tasman Drive San Jose, CA 95134-1706 USA Phone: +1 408 527-8213 EMail: email@example.com Appendix A - Changes from RFC 1885 Version 2-02 - Excluded mentioning informational replies from paragraph (f.2) of section 2.4. - In "Upper layer notification" sections changed "upper-layer protocol" and "User Interface" to "process". - Changed section 5.2, item 2 and 3 to also refer to AH authentication. - Removed item 5. from section 5.2 on denial of service attacks. - Updated phone numbers and Email addresses in the "Authors' Addresses" section. Version 2-01 - Replaced all references to "576 octets" as the maximum for an ICMP message size with "minimum IPv6 MTU" as defined by the base IPv6 specification. - Removed rate control from informational messages. - Added requirement that receivers ignore Code value in Packet Too Big message. - Removed "Not a Neighbor" (code 2) from destination unreachable message. - Fixed typos and update references. Version 2-00 - Applied rate control to informational messages - Removed section 2.4 on Group Management ICMP messages - Removed references to IGMP in Abstract and Section 1. - Updated references to other IPv6 documents - Removed references to RFC-1112 in Abstract, and Section 1, and to RFC-1191 in section 1, and section 3.2 - Added security section - Added Appendix A - changes Full Copyright Statement Copyright (C) The Internet Society (1998). All Rights Reserved. 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