Request for Comments: 4620
B. Haberman, Ed.
IPv6 Node Information Queries
Status of This Memo
This memo defines an Experimental Protocol for the Internet community. It does not specify an Internet standard of any kind. Discussion and suggestions for improvement are requested. Distribution of this memo is unlimited.
Copyright © The Internet Society (2006).
This document describes a protocol for asking an IPv6 node to supply certain network information, such as its hostname or fully-qualified domain name. IPv6 implementation experience has shown that direct queries for a hostname are useful, and a direct query mechanism for other information has been found useful in serverless environments and for debugging.
Table of Contents
1. Introduction ....................................................2 2. Applicability Statement .........................................2 3. Terminology .....................................................2 4. Node Information Messages .......................................3 5. Message Processing ..............................................5 6. Defined Qtypes ..................................................6 6.1. NOOP .......................................................7 6.2. Node Name ..................................................7 6.3. Node Addresses .............................................8 6.4. IPv4 Addresses .............................................9 6.4.1. Discussion ..........................................9 7. IANA Considerations ............................................10 8. Security Considerations ........................................10 9. Acknowledgements ...............................................11 10. References ....................................................11 10.1. Normative References .....................................11 10.2. Informative References ...................................12
This document specifies a mechanism for discovering information about names and addresses. The applicability of these mechanisms is currently limited to diagnostic and debugging tools and network management (e.g., node discovery). In the global internet, the Domain Name System (DNS)  is the authoritative source of such information and this specification is not intended to supplant or supersede it. In fact, in a well-supported network, the names and addresses dealt with by this mechanism will be the same ones, with the same relationships, as those listed in the DNS.
This new Node Information protocol provides facilities that are not found in the DNS, for example, discovering relationships between addresses without reference to names. The functions that do overlap with the DNS may be useful in serverless environments, for debugging, or in regard to link-local and unique-local addresses  that often will not be listed in the DNS.
2. Applicability Statement
IPv6 Node Information Queries include the capability to provide forward and reverse name lookups independent of the DNS by sending packets directly to IPv6 nodes or groups of nodes.
The applicability of these mechanisms is currently limited to diagnostic and debugging tools and network management (e.g., node discovery). These mechanisms can be used to learn the addresses and names for nodes on the other end of a point-to-point link or nodes on a shared-medium link such as an Ethernet. This is very useful when debugging problems or when bringing up IPv6 service where there is no global routing or DNS name services available. IPv6's large auto- configured addresses make debugging network problems and bringing up IPv6 service difficult without these mechanisms. An example of an IPv6 debugging tool using IPv6 Node Information Queries is the ping6 program in the KAME (http://www.kame.net), USAGI, and other IPv6 implementations.
The mechanisms defined in this document may have wider applicability in the future, but any use beyond debugging and diagnostic tools is left for further study and is beyond the scope of this document.
A "Node Information Query" (or "NI Query") message is sent by a "Querier" node to a "Responder" node in an ICMPv6 packet addressed to the "Queried Address". The Query contains a "Subject Address" (which may differ from the Queried Address and may be an IPv6 or IPv4 address) or a "Subject Name". The Responder sends a "Node Information Reply" to the Querier, containing information associated with the node at the Queried Address. A node receiving an NI Query will be termed a Responder even if it does not send a reply.
The word "name" in this document refers to a hostname with or without the domain. Where necessary, the cases of fully-qualified and single-label names will be distinguished.
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 .
Packet fields marked "unused" must be zero on transmission and, aside from inclusion in checksums or message integrity checks, ignored on reception.
4. Node Information Messages
Two types of Node Information messages, the NI Query and the NI Reply, are carried in ICMPv6  packets. They have the same 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Qtype | Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + Nonce + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | / Data / | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Node Information Messages
* 139 - NI Query * 140 - NI Reply
- For NI Query
- 0 - Indicates that the Data field contains an IPv6 address that is the Subject of this Query.
- 1 - Indicates that the Data field contains a name that is the Subject of this Query, or is empty, as in the case of a NOOP.
- 2 - Indicates that the Data field contains an IPv4 address that is the Subject of this Query.
- For NI Reply
- 0 - Indicates a successful reply. The Reply Data field may or may not be empty.
+ 1 - Indicates that the Responder refuses to supply the
answer. The Reply Data field will be empty.
- 2 - Indicates that the Qtype of the Query is unknown to the Responder. The Reply Data field will be empty.
- Checksum - The ICMPv6 checksum.
- Qtype - A 16-bit field that designates the type of information requested in a Query or supplied in a Reply. Its value in a Reply is always copied from the corresponding Query by the Responder. Five values of Qtype are specified in this document.
- Flags - Qtype-specific flags that may be defined for certain Query types and their Replies. Flags not defined for a given Qtype must be zero on transmission and ignored on reception, and must not be copied from a Query to a Reply unless so specified in the definition of the Qtype.
- Nonce - An opaque 64-bit field to help avoid spoofing and/or to aid in matching Replies with Queries. Its value in a Query is chosen by the Querier. Its value in a Reply is always copied from the corresponding Request by the Responder.
- Data - In a Query, the Subject Address or Name. In a Reply, Qtype-specific data is present only when the ICMPv6 Code field is zero. The length of the Data may be inferred from the IPv6 header's Payload Length field , the length of the fixed portion of the NI packet, and the lengths of the ICMPv6 header and intervening extension headers.
Note that the type of information present in the Data field of a Query is declared by the ICMP Code, whereas the type of information, if any, in the Data field of a Reply is determined by the Qtype.
When the Subject of a Query is a name, the name MUST be in DNS wire format . The name may be either a fully-qualified domain name, including the terminating zero-length label, or a single DNS label followed by two zero-length labels. Since a Query contains at most one name, DNS name compression MUST NOT be used.
5. Message Processing
The Querier constructs an ICMP NI Query and sends it to the address from which information is wanted. When the Subject of the Query is an IPv6 address, that address will normally be used as the IPv6 destination address of the Query, but need not be if the Querier has useful a priori information about the addresses of the target node. An NI Query may also be sent to a multicast address of link-local scope .
When the Subject is a name, either fully-qualified or single- component, and the Querier does not have a unicast address for the target node, the query MUST be sent to a link-scope multicast address formed in the following way. The Subject Name is converted to the canonical form defined by DNS Security , which is uncompressed with all alphabetic characters in lowercase. (If additional DNS label types or character sets for hostnames are defined, the rules for canonicalizing those labels will be found in their defining specification.) Compute the MD5 hash  of the first label of the Subject Name--the portion beginning with the first one-octet length field and up to, but excluding, any subsequent length field. Append the first 24 bits of that 128-bit hash to the prefix FF02:0:0:0:0:2:FF00::/104. The resulting multicast address will be termed the "NI Group Address" for the name. A node will support an "NI Group Address" for each unique single-label name.
The Nonce MUST be a random or good pseudo-random value to foil spoofed replies. An implementation that allows multiple independent processes to send NI Queries MAY use the Nonce value to deliver Replies to the correct process. Nonetheless, such processes MUST check the received Nonce and ignore extraneous Replies.
If true communication security is required, IP Security (IPsec)  should be used. Providing the infrastructure to authenticate NI
Queries and Replies may be quite difficult outside of a well-defined community.
Upon receiving an NI Query, the Responder must check the Query's IPv6 destination address and discard the Query without further processing unless it is one of the Responder's unicast or anycast addresses, or a link-local scope multicast address that the Responder has joined. Typically, the latter will be an NI Group Address for a name belonging to the Responder. A node MAY be configured to discard NI Queries to multicast addresses other than its NI Group Address(es), but if so, the default configuration SHOULD be not to discard them.
A Responder must also silently discard a Query whose Subject Address or Name (in the Data field) does not belong to that node. A single- component Subject Name matches any fully-qualified name whose first label matches the Subject. All name matching is done in a case- independent manner consistent with DNS Security (DNSSEC) name canonicalization .
Next, if Qtype is unknown to the Responder, it must return an NI Reply with ICMPv6 Code = 2 and no Reply Data. The Responder should rate-limit such replies as it would ICMPv6 error replies .
Next, the Responder should decide whether to refuse an answer, based on local policy. (See the "Security Considerations" section for recommended default behavior.) If an answer is refused, depending on local policy the Responder can elect to silently discard the query or send an NI Reply with ICMPv6 Code = 1 and no Reply Data. Again, the Responder should rate-limit such replies as it would ICMPv6 error replies .
Finally, if the Qtype is known and the response is allowed by local policy, the Responder MUST fill in the Flags and Reply Data of the NI Reply in accordance with the definition of the Qtype and transmit the NI Reply. The source address of the NI Reply SHOULD be selected using the rules defined in .
If the Query was sent to a multicast address, transmission of the Reply MUST be delayed by a random interval between zero and [Query Response Interval], as defined by Multicast Listener Discovery Version 2 .
6. Defined Qtypes
The following Qtypes are defined. Qtypes 0, 2, and 3 MUST be supported by any implementation of this protocol. Qtype 4 SHOULD be supported by any implementation of this protocol on an IPv4/IPv6 dual-stack node and MAY be supported on an IPv6-only node.
+-------------+----------------+ | Qtype Value | Qtype Name | +-------------+----------------+ | 0 | NOOP | | 1 | unused | | 2 | Node Name | | 3 | Node Addresses | | 4 | IPv4 Addresses | +-------------+----------------+
This NI type has no defined flags and never has a Data field. A Reply to an NI NOOP Query tells the Querier that a node with the Queried Address is up and reachable and implements the Node Information protocol. On transmission, the ICMPv6 Code in a NOOP Query must be set to 1 and the Code in a NOOP Reply must be 0. On reception of a NOOP Query or Reply, the Code must be ignored.
6.2. Node Name
The NI Node Name Query requests the fully-qualified or single- component name corresponding to the Subject Address or Name. The Reply Data has the following 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Node Names ... | + + / / + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Node Information Reply Message
- TTL (Time to Live) - MUST be zero. Any non-zero value received MUST be treated as zero. This field is no longer used but is present to preserve backward compatibility with older implementations.
- Node Names - The fully-qualified or single-component name or names of the Responder that correspond(s) to the Subject Address or Name, in DNS wire format, Section 3.1 of . Each name MUST be fully-qualified if the responder knows the domain suffix; otherwise, each name MUST be a single DNS label followed by two zero-length labels. When multiple node names are returned and more than one of them is fully-qualified, DNS name compression, Section 4.1.4 of , SHOULD be used, and the offsets are counted from the first octet of the Data field. An offset of 4, for example, will point to the beginning of the first name.
The Responder must fill in the TTL field of the Reply with zero.
Only one TTL is included in the Reply.
If the Responder does not know its name at all, it MUST send a Reply with TTL=0 and no Node Names (or a Reply with Code=1 indicating refusal to answer). The Querier will be able to determine from the packet length that the Data field contains no names.
6.3. Node Addresses
The NI Node Addresses Query requests some set of the Responder's IPv6 unicast addresses. The Reply Data is a sequence of 128-bit IPv6 addresses, with each address preceded by a separate 32-bit TTL value, with Preferred addresses listed before Deprecated addresses ; otherwise, they are in no special order. Five flag bits are defined in the Query and six in the Reply.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Qtype=3 | unused |G|S|L|C|A|T| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Node Information Address Query
- G - If set to 1, Global-scope addresses  are requested.
- S - If set to 1, Site-local addresses  are requested. However, Site-local addresses are now deprecated  and this flag is for backward compatibility.
- L - If set to 1, Link-local addresses  are requested.
- C - If set to 1, IPv4-compatible (now deprecated) and IPv4-mapped addresses  are requested. Responses SHOULD include IPv4 addresses in IPv4-mapped form.
- A - If set to 1, all the Responder's unicast addresses (of the specified scope(s)) are requested. If 0, only those addresses are requested that belong to the interface (or any one interface) that has the Subject Address or that are associated with the Subject Name.
- T - Defined in a Reply only, indicates that the set of addresses is incomplete for space reasons.
Flags G, S, L, C, and A are copied from a Query to the corresponding Reply.
The TTL associated with each address MUST be zero.
6.4. IPv4 Addresses
The NI IPv4 Addresses Query requests some set of the Responder's IPv4 unicast addresses. The Reply Data is a sequence of 32-bit IPv4 addresses, each address preceded by a 32-bit TTL value. One flag bit is defined in the Query and two in the Reply.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Qtype=4 | unused |A|T| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Node Information IPv4 Address Query
- A - If set to 1, all the Responder's unicast addresses are requested. If 0, only those addresses are requested that belong to the interface (or any one interface) that has the Subject Address.
- T - Defined in a Reply only, indicates that the set of addresses is incomplete for space reasons.
Flag A is copied from a Query to the corresponding Reply.
The TTL associated with each address MUST be zero.
It is possible that a node may treat IPv4 interfaces and IPv6 interfaces as distinct, even though they are associated with the same hardware. When such a node is responding to an NI Query having a Subject Address of one type requesting the other type, and the Query has the A flag set to 0, it SHOULD consider IP interfaces, other than tunnels, associated with the same hardware as being the same interface.
7. IANA Considerations
ICMPv6 type values 139 and 140 were previously assigned by IANA for this protocol. This document defines three values of the ICMPv6 Code field for each of these ICMPv6 Type values. Additional Code values may be defined using the "Specification Required" criteria from . IANA has established and will maintain a registry for the Code fields associated with the Node Information Query ICMPv6 Types as a part of its ICMPv6 Registry updated in .
This document defines five values of Qtype, numbers 0 through 4. Following the policies outlined in , new values, and their associated Flags and Reply Data, are to be defined by IETF Consensus.
The IANA has assigned the IPv6 multicast prefix FF02:0:0:0:0:2:FF00::/104 for use in Node Information Queries as defined in Section 5. It should be noted that this assignment does conform with the requirements defined in .
8. Security Considerations
This protocol shares the security issues of ICMPv6 that are documented in the "Security Considerations" section of .
This protocol has the potential of revealing information useful to a would-be attacker. An implementation of this protocol MUST have a default configuration that refuses to answer queries from global- scope  addresses.
Implementations SHOULD apply rate-limiting to NI responses to avoid being used in a denial-of-service attack.
The anti-spoofing Nonce does not give any protection from spoofers who can eavesdrop the Query or the Reply.
The information learned via this protocol SHOULD NOT be trusted for making security-relevant decisions unless some other mechanisms beyond the scope of this document are used to authenticate this information.
An implementation of this protocol SHOULD provide the ability to control the dissemination of information related to IPv6 Privacy Addresses . The default action of this policy SHOULD NOT provide a response to a Query that contains a node's Privacy Addresses.
A node MUST NOT include Privacy Addresses in any Node Addresses response that includes a public address, or for which the source address of the response, the destination address of the request, or the Subject Address of the request is a public address. Similarly, a node MUST NOT include any address other than the (single) Privacy Address in any Node Addresses response that includes the Privacy Address, or for which the source address of the response, the destination address of the request, or the Subject Address of the request is the Privacy Address.
Alain Durand contributed to this specification, and valuable feedback and implementation experience were provided by Jun-Ichiro Hagino and Tatuya Jinmei. Other useful comments were received from Robert Elz, Keith Moore, Elwyn Davies, Pekka Savola, and Dave Thaler. Bob Hinden and Brian Haberman have acted as document editors during the IETF advancement process.
This document is not the first proposal of a direct query mechanism for address-to-name translation. The idea had been discussed briefly in the IPng working group, and RFC 1788  describes such a mechanism for IPv4.
10.1. Normative References
 Mockapetris, P., "Domain names - concepts and facilities", STD 13, RFC 1034, November 1987.  Mockapetris, P., "Domain names - implementation and specification", STD 13, RFC 1035, November 1987.  Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, February 2006.  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.  Conta, A. and S. Deering, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", RFC 2463, December 1998.  Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998.  Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "Resource Records for the DNS Security Extensions", RFC 4034, March 2005.  Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321, April 1992.  Draves, R., "Default Address Selection for Internet Protocol version 6 (IPv6)", RFC 3484, February 2003.  Vida, R. and L. Costa, "Multicast Listener Discovery Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.  Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 2461, December 1998.  Hinden, R., Deering, S., and E. Nordmark, "IPv6 Global Unicast Address Format", RFC 3587, August 2003.  Conta, A., Deering, S., and M. Gupta, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", RFC 4443, March 2006.
10.2. Informative References
 Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, December 2005.  Huitema, C. and B. Carpenter, "Deprecating Site Local Addresses", RFC 3879, September 2004.  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.  Haberman, B., "Allocation Guidelines for IPv6 Multicast Addresses", RFC 3307, August 2002.  Narten, T. and R. Draves, "Privacy Extensions for Stateless Address Autoconfiguration in IPv6", RFC 3041, January 2001.  Simpson, W., "ICMP Domain Name Messages", RFC 1788, April 1995.
Matt Crawford Fermilab PO Box 500 Batavia, IL 60510 US Phone: +1 630 840 3461 EMail: firstname.lastname@example.org Brian Haberman (editor) Johns Hopkins University Applied Physics Lab 11100 Johns Hopkins Road Laurel, MD 20723-6099 US Phone: +1 443 778 1319 EMail: email@example.com
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