NetworkDNSEXT Working Group M. Stapp Internet-Draft Cisco Systems, Inc. Expires: June 1,August 31, 2001 T. Lemon A. Gustafsson Nominum, Inc. December 2000March 2, 2001 A DNS RR for Encoding DHCP Information <draft-ietf-dnsext-dhcid-rr-01.txt><draft-ietf-dnsext-dhcid-rr-02.txt> Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on June 1,August 31, 2001. Copyright Notice Copyright (C) The Internet Society (2000).(2001). All Rights Reserved. Abstract A situation can arise where multiple DHCP clients request the same DNS name from their (possibly distinct) DHCP servers. To resolve such conflicts, 'Resolution of DNS Name Conflicts'Conflicts' proposes storing client identifiers in the DNS to unambiguously associate domain names with the DHCP clients "owning" them. This memo defines a distinct RR type for use by DHCP servers, the "DHCID" RR. Table of Contents 1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. The DHCID RR . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. DHCID RDATA format . . . . . . . . . . . . . . . . . . . . . . 3 4.1 Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . 4 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 45 7. Appendix A: Base 64 Encoding . . . . . . . . . . . . . . . . . 45 References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 67 Full Copyright Statement . . . . . . . . . . . . . . . . . . . 8 1. 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 RFC 2119. 2. Introduction A set of procedures to allow DHCP clients and servers to automatically update the DNS (RFC1034, RFC1035)(RFC1034, RFC1035) is proposed in "Resolution of DNS Name Conflicts".Conflicts". A situation can arise where multiple DHCP clients wish to use the same DNS name. To resolve such conflicts, Resolution of DNS Name ConflictsConflicts proposes storing client identifiers in the DNS to unambiguously associate domain names with the DHCP clients using them. In the interest of clarity, it would be preferable for this DHCP information to use a distinct RR type. This memo defines a distinct RR type for this purpose for use by DHCP clients or servers, the "DHCID" RR. 3. The DHCID RR The DHCID RR is defined with mnemonic DHCID and type code [TBD]. 4. DHCID RDATA format The RDATA section of a DHCID RR in transmission contains RDLENGTH bytes 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. In DNS master files, the RDATA is represented in base 64 encoding (see Appendix A)A (Section 7)) and may be divided up into any number of white space separated substrings, down to single base 64 digits, which are concatenated to obtain the full signature. These substrings can span lines using the standard parenthesis. This format is identical to that used for representing binary data in DNSSEC (RFC2535).(RFC2535). 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 safely perform dynamic DNS updates to the same zone. From the updater's perspective, the DHCID resource record consists of a 16-bit identifier type, followed by one or more bytes representing the actual identifier. There are two possible forms for a DHCID RR -The type code can have one of three classes of values. The first class contains just the value zero. This type indicates that is used whenthe DHCP server is usingremaining contents of the client's link-layer address to identify it, and oneDHCID record encode an identifier that is used when the DHCP server is using some DHCP option that the DHCP client sent to identify it. Whenbased on the client's link-layer addressnetwork address. The second class of types contains just the value 0xFFFF. This type code is used asreserved for future extensibility. The third class of types contains all the identifier,values not included in the first two bytes- that is, every value other than zero or 0xFFFF. Types in this class indicate that the remaining contents of the RRDATA are set to 0. When aDHCID record encode an identifier that is based on the DHCP option whose code is usedthe same as the identifier,specified type. The most common value in this class at the first two bytestime of the RRDATA containwriting of this draft is 61, which is the DHCP option number, in network byte order. The two bytes 0xffff are reservedcode for future extensibility. In both cases,the remainder ofClient Identifier option. The data following the RRDATAtype code (for type codes other than 0xFFFF) is the result of performingderived by running a one-way hash across the identifier.identifying information. The details of the method used to generate the data in the RR and the use to which a DHCP client or server may putthis associationare beyond the scope of this draft, and are discussedspecified in the specification of the DNS update behavior, 'Resolution"Resolution of DNS Name Conflicts'.Conflicts". This RR MUST NOT be used for any purpose other than that detailed in the DHC document."Resolution of DNS Name Conflicts". Althought this RR contains data that is opaque to DNS servers, the data is meaningful to DHCP updaters.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.Group, as a result of revising . 4.1 Example A DHCP server allocating the IPv4 address 10.0.0.1 to a client "client.org.nil" might use the client's link-layer address to identify the client: client.org.nil. A 10.0.0.1 client.org.nil. DHCID AAAY KREX Igqt wYgQ o93/ yNlJAAAYKREXIgqtwYgQo93/yNlJ A DHCP server allocating the IPv4 address 10.0.12.99 to a client "chi.org.nil" might use the DHCP client identifier option to identify the client: chi.org.nil. A 10.0.12.99 chi.org.nil. DHCID AGGS cSLa AYjd OhGM HKD/ lJ2BAGGScSLaAYjdOhGMHKD/lJ2B 5. Security Considerations The DHCID record as such does not introduce any new security problems into the DNS. In order to avoid exposing private information about DHCP clients to public scrutiny, a one-way-hash is used to obscure all client information. 6. IANA Considerations IANA is requested to allocate an RR type number for the DHCID record type. 7. Appendix A: Base 64 Encoding The following encoding technique is taken from RFC 20452045 by N. Borenstein and N. Freed. It is reproduced here in an edited form for convenience. A 65-character subset of US-ASCII is used, enabling 6 bits to be represented per printable character. (The extra 65th character, "=", is used to signify a special processing function.) The encoding process represents 24-bit groups of input bits as output strings of 4 encoded characters. Proceeding from left to right, a 24-bit input group is formed by concatenating 3 8-bit input groups. These 24 bits are then treated as 4 concatenated 6-bit groups, each of which is translated into a single digit in the base 64 alphabet. Each 6-bit group is used as an index into an array of 64 printable characters. The character referenced by the index is placed in the output string. The Base 64 Alphabet Value Encoding Value Encoding Value Encoding Value Encoding 0 A 17 R 34 i 51 z 1 B 18 S 35 j 52 0 2 C 19 T 36 k 53 1 3 D 20 U 37 l 54 2 4 E 21 V 38 m 55 3 5 F 22 W 39 n 56 4 6 G 23 X 40 o 57 5 7 H 24 Y 41 p 58 6 8 I 25 Z 42 q 59 7 9 J 26 a 43 r 60 8 10 K 27 b 44 s 61 9 11 L 28 c 45 t 62 + 12 M 29 d 46 u 63 / 13 N 30 e 47 v 14 O 31 f 48 w (pad) = 15 P 32 g 49 x 16 Q 33 h 50 y Special processing is performed if fewer than 24 bits are available at the end of the data being encoded. A full encoding quantum is always completed at the end of a quantity. When fewer than 24 input bits are available in an input group, zero bits are added (on the right) to form an integral number of 6-bit groups. Padding at the end of the data is performed using the '=' character. Since all base 64 input is an integral number of octets, only the following cases can arise: (1) the final quantum of encoding input is an integral multiple of 24 bits; here, the final unit of encoded output will be an integral multiple of 4 characters with no "=" padding, (2) the final quantum of encoding input is exactly 8 bits; here, the final unit of encoded output will be two characters followed by two "=" padding characters, or (3) the final quantum of encoding input is exactly 16 bits; here, the final unit of encoded output will be three characters followed by one "=" padding character. References  Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997.  Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, Mar 1997.  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor Extensions", RFC 2132, Mar 1997.  Mockapetris, P., "Domain names - Concepts and Facilities", RFC 1034, Nov 1987.  Mockapetris, P., "Domain names - Implementation and Specification", RFC 1035, Nov 1987.  Stapp, M., "Resolution of DNS Name Conflicts Among DHCP Clients (draft-ietf-dhc-dns-resolution-*)", July 2000.  Eastlake, D., "Domain Name System Security Extensions", RFC 2535, March 1999.  Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies", RFC 2045, November 1996. Authors' Addresses Mark Stapp Cisco Systems, Inc. 250 Apollo Dr. Chelmsford, MA 01824 USA Phone: 978.244.8498 EMail: email@example.com Ted Lemon Nominum, Inc. 950 Charter St. Redwood City, CA 94063 USA EMail: firstname.lastname@example.org Andreas Gustafsson Nominum, Inc. 950 Charter St. Redwood City, CA 94063 USA EMail: email@example.com Full Copyright Statement Copyright (C) The Internet Society (2000).(2001). All Rights Reserved. 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