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diff --git a/doc/rfc/rfc4701.txt b/doc/rfc/rfc4701.txt new file mode 100644 index 00000000..03e3c543 --- /dev/null +++ b/doc/rfc/rfc4701.txt @@ -0,0 +1,675 @@ + + + + + + +Network Working Group M. Stapp +Request for Comments: 4701 Cisco Systems, Inc. +Category: Standards Track T. Lemon + Nominum, Inc. + A. Gustafsson + Araneus Information Systems Oy + October 2006 + + + A DNS Resource Record (RR) for Encoding + Dynamic Host Configuration Protocol (DHCP) Information (DHCID RR) + +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 + + It is possible for Dynamic Host Configuration Protocol (DHCP) clients + to attempt to update the same DNS Fully Qualified Domain Name (FQDN) + or to update a DNS FQDN that has been added to the DNS for another + purpose as they obtain DHCP leases. Whether the DHCP server or the + clients themselves perform the DNS updates, conflicts can arise. To + resolve such conflicts, RFC 4703 proposes storing client identifiers + in the DNS to unambiguously associate domain names with the DHCP + clients to which they refer. This memo defines a distinct Resource + Record (RR) type for this purpose for use by DHCP clients and + servers: the "DHCID" RR. + + + + + + + + + + + + + + + +Stapp, et al. Standards Track [Page 1] + +RFC 4701 The DHCID RR October 2006 + + +Table of Contents + + 1. Introduction ....................................................3 + 2. Terminology .....................................................3 + 3. The DHCID RR ....................................................3 + 3.1. DHCID RDATA Format .........................................3 + 3.2. DHCID Presentation Format ..................................4 + 3.3. The DHCID RR Identifier Type Codes .........................4 + 3.4. The DHCID RR Digest Type Code ..............................4 + 3.5. Computation of the RDATA ...................................5 + 3.5.1. Using the Client's DUID .............................5 + 3.5.2. Using the Client Identifier Option ..................6 + 3.5.3. Using the Client's htype and chaddr .................6 + 3.6. Examples ...................................................6 + 3.6.1. Example 1 ...........................................6 + 3.6.2. Example 2 ...........................................7 + 3.6.3. Example 3 ...........................................7 + 4. Use of the DHCID RR .............................................8 + 5. Updater Behavior ................................................8 + 6. Security Considerations .........................................8 + 7. IANA Considerations .............................................9 + 8. Acknowledgements ................................................9 + 9. References ......................................................9 + 9.1. Normative References .......................................9 + 9.2. Informative References ....................................10 + + + + + + + + + + + + + + + + + + + + + + + + + + +Stapp, et al. Standards Track [Page 2] + +RFC 4701 The DHCID RR October 2006 + + +1. Introduction + + A set of procedures to allow DHCP [7] [11] clients and servers to + automatically update the DNS ([3], [4]) is proposed in [1]. + + Conflicts can arise if multiple DHCP clients wish to use the same DNS + name or a DHCP client attempts to use a name added for another + purpose. To resolve such conflicts, [1] proposes storing client + identifiers in the DNS to unambiguously associate domain names with + the DHCP clients using them. In the interest of clarity, it is + preferable for this DHCP information to use a distinct RR type. This + memo defines a distinct RR for this purpose for use by DHCP clients + or servers: the "DHCID" RR. + + In order to obscure potentially sensitive client identifying + information, the data stored is the result of a one-way SHA-256 hash + computation. The hash includes information from the DHCP client's + message as well as the domain name itself, so that the data stored in + the DHCID RR will be dependent on both the client identification used + in the DHCP protocol interaction and the domain name. This means + that the DHCID RDATA will vary if a single client is associated over + time with more than one name. This makes it difficult to 'track' a + client as it is associated with various domain names. + +2. Terminology + + 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 [2]. + +3. The DHCID RR + + The DHCID RR is defined with mnemonic DHCID and type code 49. The + DHCID RR is only defined in the IN class. DHCID RRs cause no + additional section processing. + +3.1. DHCID RDATA Format + + The RDATA section of a DHCID RR in transmission contains RDLENGTH + octets of binary data. The format of this data and its + interpretation by DHCP servers and clients are described below. + + DNS software should consider the RDATA section to be opaque. DHCP + clients or servers use the DHCID RR to associate a DHCP client's + identity with a DNS name, so that multiple DHCP clients and servers + may deterministically perform dynamic DNS updates to the same zone. + From the updater's perspective, the DHCID resource record RDATA + consists of a 2-octet identifier type, in network byte order, + + + +Stapp, et al. Standards Track [Page 3] + +RFC 4701 The DHCID RR October 2006 + + + followed by a 1-octet digest type, followed by one or more octets + representing the actual identifier: + + < 2 octets > Identifier type code + < 1 octet > Digest type code + < n octets > Digest (length depends on digest type) + +3.2. DHCID Presentation Format + + In DNS master files, the RDATA is represented as a single block in + base-64 encoding identical to that used for representing binary data + in [8], Section 3. The data may be divided up into any number of + white-space-separated substrings, down to single base-64 digits, + which are concatenated to form the complete RDATA. These substrings + can span lines using the standard parentheses. + +3.3. The DHCID RR Identifier Type Codes + + The DHCID RR Identifier Type Code specifies what data from the DHCP + client's request was used as input into the hash function. The + identifier type codes are defined in a registry maintained by IANA, + as specified in Section 7. The initial list of assigned values for + the identifier type code and that type's identifier is: + + + +------------------+------------------------------------------------+ + | Identifier Type | Identifier | + | Code | | + +------------------+------------------------------------------------+ + | 0x0000 | The 1-octet 'htype' followed by 'hlen' octets | + | | of 'chaddr' from a DHCPv4 client's DHCPREQUEST | + | | [7]. | + | 0x0001 | The data octets (i.e., the Type and | + | | Client-Identifier fields) from a DHCPv4 | + | | client's Client Identifier option [10]. | + | 0x0002 | The client's DUID (i.e., the data octets of a | + | | DHCPv6 client's Client Identifier option [11] | + | | or the DUID field from a DHCPv4 client's | + | | Client Identifier option [6]). | + | 0x0003 - 0xfffe | Undefined; available to be assigned by IANA. | + | 0xffff | Undefined; RESERVED. | + +------------------+------------------------------------------------+ + +3.4. The DHCID RR Digest Type Code + + The DHCID RR Digest Type Code is an identifier for the digest + algorithm used. The digest is calculated over an identifier and the + canonical FQDN as described in the next section. + + + +Stapp, et al. Standards Track [Page 4] + +RFC 4701 The DHCID RR October 2006 + + + The digest type codes are defined in a registry maintained by IANA, + as specified in Section 7. The initial list of assigned values for + the digest type codes is: value 0 is reserved, and value 1 is + SHA-256. Reserving other types requires IETF standards action. + Defining new values will also require IETF standards action to + document how DNS updaters are to deal with multiple digest types. + +3.5. Computation of the RDATA + + The DHCID RDATA is formed by concatenating the 2-octet identifier + type code with variable-length data. + + The RDATA for all type codes other than 0xffff, which is reserved for + future expansion, is formed by concatenating the 2-octet identifier + type code, the 1-octet digest type code, and the digest value (32 + octets for SHA-256). + + < identifier-type > < digest-type > < digest > + + The input to the digest hash function is defined to be: + + digest = SHA-256(< identifier > < FQDN >) + + The FQDN is represented in the buffer in the canonical wire format as + described in [9], Section 6.2. The identifier type code and the + identifier are related as specified in Section 3.3: the identifier + type code describes the source of the identifier. + + A DHCPv4 updater uses the 0x0002 type code if a Client Identifier + option is present in the DHCPv4 messages and it is encoded as + specified in [6]. Otherwise, the updater uses 0x0001 if a Client + Identifier option is present, and 0x0000 if not. + + A DHCPv6 updater always uses the 0x0002 type code. + +3.5.1. Using the Client's DUID + + When the updater is using the Client's DUID (either from a DHCPv6 + Client Identifier option or from a portion of the DHCPv4 Client + Identifier option encoded as specified in [6]), the first two octets + of the DHCID RR MUST be 0x0002, in network byte order. The third + octet is the digest type code (1 for SHA-256). The rest of the DHCID + RR MUST contain the results of computing the SHA-256 hash across the + octets of the DUID followed by the FQDN. + + + + + + + +Stapp, et al. Standards Track [Page 5] + +RFC 4701 The DHCID RR October 2006 + + +3.5.2. Using the Client Identifier Option + + When the updater is using the DHCPv4 Client Identifier option sent by + the client in its DHCPREQUEST message, the first two octets of the + DHCID RR MUST be 0x0001, in network byte order. The third octet is + the digest type code (1 for SHA-256). The rest of the DHCID RR MUST + contain the results of computing the SHA-256 hash across the data + octets (i.e., the Type and Client-Identifier fields) of the option, + followed by the FQDN. + +3.5.3. Using the Client's htype and chaddr + + When the updater is using the client's link-layer address as the + identifier, the first two octets of the DHCID RDATA MUST be zero. + The third octet is the digest type code (1 for SHA-256). To generate + the rest of the resource record, the updater computes a one-way hash + using the SHA-256 algorithm across a buffer containing the client's + network hardware type, link-layer address, and the FQDN data. + Specifically, the first octet of the buffer contains the network + hardware type as it appeared in the DHCP 'htype' field of the + client's DHCPREQUEST message. All of the significant octets of the + 'chaddr' field in the client's DHCPREQUEST message follow, in the + same order in which the octets appear in the DHCPREQUEST message. + The number of significant octets in the 'chaddr' field is specified + in the 'hlen' field of the DHCPREQUEST message. The FQDN data, as + specified above, follows. + +3.6. Examples + +3.6.1. Example 1 + + A DHCP server allocates the IPv6 address 2001:DB8::1234:5678 to a + client that included the DHCPv6 client-identifier option data 00:01: + 00:06:41:2d:f1:66:01:02:03:04:05:06 in its DHCPv6 request. The + server updates the name "chi6.example.com" on the client's behalf and + uses the DHCP client identifier option data as input in forming a + DHCID RR. The DHCID RDATA is formed by setting the two type octets + to the value 0x0002, the 1-octet digest type to 1 for SHA-256, and + performing a SHA-256 hash computation across a buffer containing the + 14 octets from the client-id option and the FQDN (represented as + specified in Section 3.5). + + chi6.example.com. AAAA 2001:DB8::1234:5678 + chi6.example.com. DHCID ( AAIBY2/AuCccgoJbsaxcQc9TUapptP69l + OjxfNuVAA2kjEA= ) + + If the DHCID RR type is not supported, the RDATA would be encoded + [13] as: + + + +Stapp, et al. Standards Track [Page 6] + +RFC 4701 The DHCID RR October 2006 + + + \# 35 ( 000201636fc0b8271c82825bb1ac5c41cf5351aa69b4febd94e8f17cd + b95000da48c40 ) + +3.6.2. Example 2 + + A DHCP server allocates the IPv4 address 192.0.2.2 to a client that + included the DHCP client-identifier option data 01:07:08:09:0a:0b:0c + in its DHCP request. The server updates the name "chi.example.com" + on the client's behalf and uses the DHCP client identifier option + data as input in forming a DHCID RR. The DHCID RDATA is formed by + setting the two type octets to the value 0x0001, the 1-octet digest + type to 1 for SHA-256, and performing a SHA-256 hash computation + across a buffer containing the seven octets from the client-id option + and the FQDN (represented as specified in Section 3.5). + + chi.example.com. A 192.0.2.2 + chi.example.com. DHCID ( AAEBOSD+XR3Os/0LozeXVqcNc7FwCfQdW + L3b/NaiUDlW2No= ) + + If the DHCID RR type is not supported, the RDATA would be encoded + [13] as: + + \# 35 ( 0001013920fe5d1dceb3fd0ba3379756a70d73b17009f41d58bddbfcd + 6a2503956d8da ) + +3.6.3. Example 3 + + A DHCP server allocating the IPv4 address 192.0.2.3 to a client with + the Ethernet MAC address 01:02:03:04:05:06 using domain name + "client.example.com" uses the client's link-layer address to identify + the client. The DHCID RDATA is composed by setting the two type + octets to zero, the 1-octet digest type to 1 for SHA-256, and + performing an SHA-256 hash computation across a buffer containing the + 1-octet 'htype' value for Ethernet, 0x01, followed by the six octets + of the Ethernet MAC address, and the domain name (represented as + specified in Section 3.5). + + client.example.com. A 192.0.2.3 + client.example.com. DHCID ( AAABxLmlskllE0MVjd57zHcWmEH3pCQ6V + ytcKD//7es/deY= ) + + If the DHCID RR type is not supported, the RDATA would be encoded + [13] as: + + \# 35 ( 000001c4b9a5b249651343158dde7bcc77169841f7a4243a572b5c283 + fffedeb3f75e6 ) + + + + + +Stapp, et al. Standards Track [Page 7] + +RFC 4701 The DHCID RR October 2006 + + +4. Use of the DHCID RR + + This RR MUST NOT be used for any purpose other than that detailed in + [1]. Although this RR contains data that is opaque to DNS servers, + the data must be consistent across all entities that update and + interpret this record. Therefore, new data formats may only be + defined through actions of the DHC Working Group, as a result of + revising [1]. + +5. Updater Behavior + + The data in the DHCID RR allows updaters to determine whether more + than one DHCP client desires to use a particular FQDN. This allows + site administrators to establish policy about DNS updates. The DHCID + RR does not establish any policy itself. + + Updaters use data from a DHCP client's request and the domain name + that the client desires to use to compute a client identity hash, and + then compare that hash to the data in any DHCID RRs on the name that + they wish to associate with the client's IP address. If an updater + discovers DHCID RRs whose RDATA does not match the client identity + that they have computed, the updater SHOULD conclude that a different + client is currently associated with the name in question. The + updater SHOULD then proceed according to the site's administrative + policy. That policy might dictate that a different name be selected, + or it might permit the updater to continue. + +6. Security Considerations + + The DHCID record as such does not introduce any new security problems + into the DNS. In order to obscure the client's identity information, + a one-way hash is used. Further, in order to make it difficult to + 'track' a client by examining the names associated with a particular + hash value, the FQDN is included in the hash computation. Thus, the + RDATA is dependent on both the DHCP client identification data and on + each FQDN associated with the client. + + However, it should be noted that an attacker that has some knowledge, + such as of MAC addresses commonly used in DHCP client identification + data, may be able to discover the client's DHCP identify by using a + brute-force attack. Even without any additional knowledge, the + number of unknown bits used in computing the hash is typically only + 48 to 80. + + Administrators should be wary of permitting unsecured DNS updates to + zones, whether or not they are exposed to the global Internet. Both + DHCP clients and servers SHOULD use some form of update + authentication (e.g., [12]) when performing DNS updates. + + + +Stapp, et al. Standards Track [Page 8] + +RFC 4701 The DHCID RR October 2006 + + +7. IANA Considerations + + IANA has allocated a DNS RR type number for the DHCID record type. + + This specification defines a new number-space for the 2-octet + identifier type codes associated with the DHCID RR. IANA has + established a registry of the values for this number-space. Three + initial values are assigned in Section 3.3, and the value 0xFFFF is + reserved for future use. New DHCID RR identifier type codes are + assigned through Standards Action, as defined in [5]. + + This specification defines a new number-space for the 1-octet digest + type codes associated with the DHCID RR. IANA has established a + registry of the values for this number-space. Two initial values are + assigned in Section 3.4. New DHCID RR digest type codes are assigned + through Standards Action, as defined in [5]. + +8. Acknowledgements + + Many thanks to Harald Alvestrand, Ralph Droms, Olafur Gudmundsson, + Sam Hartman, Josh Littlefield, Pekka Savola, and especially Bernie + Volz for their review and suggestions. + +9. References + +9.1. Normative References + + [1] Stapp, M. and B. Volz, "Resolution of Fully Qualified Domain + Name (FQDN) Conflicts among Dynamic Host Configuration Protocol + (DHCP) Clients", RFC 4703, October 2006. + + [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement + Levels", BCP 14, RFC 2119, March 1997. + + [3] Mockapetris, P., "Domain names - concepts and facilities", + STD 13, RFC 1034, November 1987. + + [4] Mockapetris, P., "Domain names - implementation and + specification", STD 13, RFC 1035, November 1987. + + [5] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA + Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. + + [6] Lemon, T. and B. Sommerfeld, "Node-specific Client Identifiers + for Dynamic Host Configuration Protocol Version Four (DHCPv4)", + RFC 4361, February 2006. + + + + + +Stapp, et al. Standards Track [Page 9] + +RFC 4701 The DHCID RR October 2006 + + +9.2. Informative References + + [7] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, + March 1997. + + [8] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", + RFC 3548, July 2003. + + [9] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, + "Resource Records for the DNS Security Extensions", RFC 4034, + March 2005. + + [10] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor + Extensions", RFC 2132, March 1997. + + [11] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., and M. + Carney, "Dynamic Host Configuration Protocol for IPv6 + (DHCPv6)", RFC 3315, July 2003. + + [12] Vixie, P., Gudmundsson, O., Eastlake, D., and B. Wellington, + "Secret Key Transaction Authentication for DNS (TSIG)", + RFC 2845, May 2000. + + [13] Gustafsson, A., "Handling of Unknown DNS Resource Record (RR) + Types", RFC 3597, September 2003. + + + + + + + + + + + + + + + + + + + + + + + + + + +Stapp, et al. Standards Track [Page 10] + +RFC 4701 The DHCID RR October 2006 + + +Authors' Addresses + + Mark Stapp + Cisco Systems, Inc. + 1414 Massachusetts Ave. + Boxborough, MA 01719 + USA + + Phone: 978.936.1535 + EMail: mjs@cisco.com + + + Ted Lemon + Nominum, Inc. + 950 Charter St. + Redwood City, CA 94063 + USA + + EMail: mellon@nominum.com + + + Andreas Gustafsson + Araneus Information Systems Oy + Ulappakatu 1 + 02320 Espoo + Finland + + EMail: gson@araneus.fi + + + + + + + + + + + + + + + + + + + + + + + +Stapp, et al. Standards Track [Page 11] + +RFC 4701 The DHCID RR October 2006 + + +Full Copyright Statement + + Copyright (C) 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 + WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. + +Intellectual Property + + The IETF takes no position regarding the validity or scope of any + Intellectual Property Rights or other rights that might be claimed to + pertain to the implementation or use of the technology described in + this document or the extent to which any license under such rights + might or might not be available; nor does it represent that it has + made any independent effort to identify any such rights. 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