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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group M. Wahl 2 INTERNET-DRAFT Critical Angle Inc. 3 Replaces: RFC 1777 T. Howes 4 Netscape Communications Corp. 5 S. Kille 6 Isode Limited 7 Expires in six months from 11 July 1997 8 Intended Category: Standards Track 10 Lightweight Directory Access Protocol (v3) 11 13 Table of Contents - see end of document. 15 1. Status of this Memo 17 This document is an Internet-Draft. Internet-Drafts are working 18 documents of the Internet Engineering Task Force (IETF), its areas, and 19 its working groups. Note that other groups may also distribute working 20 documents as Internet-Drafts. 22 Internet-Drafts are draft documents valid for a maximum of six months 23 and may be updated, replaced, or obsoleted by other documents at any 24 time. It is inappropriate to use Internet-Drafts as reference material 25 or to cite them other than as "work in progress." 27 To learn the current status of any Internet-Draft, please check the 28 "1id-abstracts.txt" listing contained in the Internet-Drafts Shadow 29 Directories on ds.internic.net (US East Coast), nic.nordu.net (Europe), 30 ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim). 32 2. Abstract 34 The protocol described in this document is designed to provide access 35 to directories supporting the X.500 models, while not incurring the 36 resource requirements of the X.500 Directory Access Protocol (DAP). 37 This protocol is specifically targeted at management applications and 38 browser applications that provide read/write interactive access to 39 directories. When used with a directory supporting the X.500 40 protocols, it is intended to be a complement to the X.500 DAP. 42 Key aspects of this version of LDAP are: 44 - All protocol elements of LDAPv2 (RFC 1777) are supported. The 45 protocol is carried directly over TCP or other transport, bypassing 46 much of the session/presentation overhead of X.500 DAP. 48 - Most protocol data elements can be encoded as ordinary strings 49 (e.g., Distinguished Names). 51 - Referrals to other servers may be returned. 53 - SASL and TLS mechanisms may be used with LDAP to provide association 54 security services. 56 - Attribute values and Distinguished Names have been internationalized 57 through the use of the ISO 10646 character set. 59 - The protocol can be extended to support new operations, and controls 60 may be used to extend existing operations. 62 - Schema is published in the directory for use by clients. 64 3. Models 66 Interest in X.500 [1] directory technologies in the Internet has led 67 to efforts to reduce the high cost of entry associated with use of 68 these technologies. This document continues the efforts to define 69 directory protocol alternatives, updating the LDAP [2] protocol 70 specification. 72 3.1. Protocol Model 74 The general model adopted by this protocol is one of clients 75 performing protocol operations against servers. In this model, a 76 client transmits a protocol request describing the operation to be 77 performed to a server. The server is then responsible for performing 78 the necessary operation(s) in the directory. Upon completion of 79 the operation(s), the server returns a response containing any results 80 or errors to the requesting client. 82 In keeping with the goal of easing the costs associated with use of 83 the directory, it is an objective of this protocol to minimize the 84 complexity of clients so as to facilitate widespread deployment of 85 applications capable of using the directory. 87 Note that although servers are required to return responses whenever 88 such responses are defined in the protocol, there is no requirement 89 for synchronous behavior on the part of either clients or servers. 90 Requests and responses for multiple operations may be exchanged 91 between a client and server in any order, provided the client 92 eventually receives a response for every request that requires one. 94 In LDAP versions 1 and 2, no provision was made for protocol servers 95 returning referrals to clients. However, for improved performance and 96 distribution this version of the protocol permits servers to return to 97 clients referrals to other servers. This allows servers to offload 98 the work of contacting other servers to progress operations. 100 Note that the core protocol operations defined in this document can be 101 mapped to a strict subset of the X.500(1997) directory abstract 102 service, so it can be cleanly provided by the DAP. However there is 103 not a one-to-one mapping between LDAP protocol operations and DAP 104 operations: server implementations acting as a gateway to X.500 105 directories may need to make multiple DAP requests. 107 3.2. Data Model 109 This section provides a brief introduction to the X.500 data model, as 110 used by LDAP. 112 The LDAP protocol assumes there are one or more servers which jointly 113 provide access to a Directory Information Tree (DIT). The tree is 114 made up of entries. Entries have names: one or more attribute values 115 from the entry form its relative distinguished name (RDN), which MUST 116 be unique among all its siblings. The concatenation of the relative 117 distinguished names of the sequence of entries from a particular 118 entry to an immediate subordinate of the root of the tree forms that 119 entry's Distinguished Name (DN), which is unique in the tree. An 120 example of a Distinguished Name is 122 CN=Steve Kille, O=Isode Limited, C=GB 124 Some servers may hold cache or shadow copies of entries, which can be 125 used to answer search and comparison queries, but will return 126 referrals or contact other servers if modification operations are 127 requested. 129 Servers which perform caching or shadowing MUST ensure that they do 130 not violate any access control constraints placed on the data by the 131 originating server. 133 The largest collection of entries, starting at an entry that is 134 mastered by a particular server, and including all its subordinates 135 and their subordinates, down to the entries which are mastered by 136 different servers, is termed a naming context. The root of the DIT 137 is a DSA-specific Entry (DSE) and not part of any naming context: 138 each server has different attribute values in the root DSE. (DSA is 139 an X.500 term for the directory server). 141 3.2.1. Attributes of Entries 143 Entries consist of a set of attributes. An attribute is a type with 144 one or more associated values. The attribute type is identified by a 145 short descriptive name and an OID (object identifier). The attribute 146 type governs whether there can be more than one value of an 147 attribute of that type in an entry, the syntax to which the values 148 must conform, the kinds of matching which can be performed on values 149 of that attribute, and other functions. 151 An example of an attribute is "mail". There may be one or more values 152 of this attribute, they must be IA5 (ASCII) strings, and they are 153 case insensitive (e.g. "foo@bar.com" will match "FOO@BAR.COM"). 155 Schema is the collection of attribute type definitions, object class 156 definitions and other information which a server uses to determine 157 how to match a filter or attribute value assertion (in a compare 158 operation) against the attributes of an entry, and whether to permit 159 add and modify operations. The definition of schema for use with 160 LDAP is given in [5] and [6]. Additional schema elements may be 161 defined in other documents. 163 Each entry MUST have an objectClass attribute. The objectClass 164 attribute specifies the object classes of an entry, which along with 165 the system and user schema determine the permitted attributes of an 166 entry. Values of this attribute may be modified by clients, but the 167 objectClass attribute cannot be removed. Servers may restrict the 168 modifications of this attribute to prevent the basic structural 169 class of the entry from being changed (e.g. one cannot change a 170 person into a country). When creating an entry or adding an 171 objectClass value to an entry, all superclasses of the named classes 172 are implicitly added as well if not already present, and the client 173 must supply values for any mandatory attributes of new superclasses. 175 Some attributes, termed operational attributes, are used by servers 176 for administering the directory system itself. They are not returned 177 in search results unless explicitly requested by name. Attributes 178 which are not operational, such as "mail", will have their schema and 179 syntax constraints enforced by servers, but servers will generally 180 not make use of their values. 182 Servers MUST NOT permit clients to add attributes to an entry unless 183 those attributes are permitted by the object class definitions, the 184 schema controlling that entry (specified in the subschema - see 185 below), or are operational attributes known to that server and used 186 for administrative purposes. Note that there is a particular 187 objectClass 'extensibleObject' defined in [5] which permits all user 188 attributes to be present in an entry. 190 Entries MAY contain, among others, the following operational 191 attributes, defined in [5]. These attributes are maintained 192 automatically by the server and are not modifiable by clients: 194 - creatorsName: the Distinguished Name of the user who added this 195 entry to the directory. 197 - createTimestamp: the time this entry was added to the directory. 199 - modifiersName: the Distinguished Name of the user who last modified 200 this entry. 202 - modifyTimestamp: the time this entry was last modified. 204 - subschemaSubentry: the Distinguished Name of the subschema entry 205 (or subentry) which controls the schema for this entry. 207 3.2.2. Subschema Entries and Subentries 209 Subschema entries are used for administering information about the 210 directory schema, in particular the object classes and attribute types 211 supported by directory servers. A single subschema entry contains 212 all schema definitions used by entries in a particular part of the 213 directory tree. 215 Servers which follow X.500(93) models SHOULD implement subschema 216 using the X.500 subschema mechanisms, and so these subschemas are not 217 ordinary entries. LDAP clients SHOULD NOT assume that servers 218 implement any of the other aspects of X.500 subschema. 219 A server which masters entries and permits clients to modify these 220 entries MUST implement and provide access to these subschema entries, 221 so that its clients may discover the attributes and object classes 222 which are permitted to be present. It is strongly recommended that 223 all other servers implement this as well. 225 The following four attributes MUST be present in all subschema 226 entries: 228 - cn: this attribute MUST be used to form the RDN of the subschema 229 entry. 231 - objectClass: the attribute MUST have at least the values "top" and 232 "subschema". 234 - objectClasses: each value of this attribute specifies an object 235 class known to the server. 237 - attributeTypes: each value of this attribute specifies an attribute 238 type known to the server. 240 These are defined in [5]. Other attributes MAY be present in subschema 241 entries, to reflect additional supported capabilities. These include 242 matchingRules, matchingRuleUse, dITStructureRules, dITContentRules, 243 nameForms and ldapSyntaxes. 245 Servers SHOULD provide the attributes createTimestamp and 246 modifyTimestamp in subschema entries, in order to allow clients to 247 maintain their caches of schema information. 249 Clients MUST only retrieve attributes from a subschema entry by 250 requesting a base object search of the entry, where the search filter 251 is "(objectClass=subschema)". (This will allow LDAPv3 servers which 252 gateway to X.500(93) to detect that subentry information is being 253 requested.) 255 3.3. Relationship to X.500 257 This document defines LDAP in terms of X.500 as an X.500 access 258 mechanism. An LDAP server MUST act in accordance with the 259 X.500(1993) series of ITU recommendations when providing the service. 260 However, it is not required that an LDAP server make use of any X.500 261 protocols in providing this service, e.g. LDAP can be mapped onto any 262 other directory system so long as the X.500 data and service model as 263 used in LDAP is not violated in the LDAP interface. 265 3.4. Server-specific Data Requirements 267 An LDAP server MUST provide information about itself and other 268 information that is specific to each server. This is represented as 269 a group of attributes located in the root DSE (DSA-Specific Entry), 270 which is named with the zero-length LDAPDN. These attributes 271 are retrievable if a client performs a base object search of the 272 root with filter "(objectClass=*)", however they are subject to 273 access control restrictions. 274 The root DSE MUST NOT be included if the client performs a subtree 275 search starting from the root. 277 Servers may allow clients to modify these attributes. 279 The following attributes of the root DSE are defined in section 5 280 of [5]. Additional attributes may be defined in other documents. 282 - namingContexts: naming contexts held in the server. Naming contexts 283 are defined in section 17 of X.501 [6]. 285 - subschemaSubentry: subschema entries (or subentries) known by this 286 server. 288 - altServer: alternative servers in case this one is later 289 unavailable. 291 - supportedExtension: list of supported extended operations. 293 - supportedControl: list of supported controls. 295 - supportedSASLMechanisms: list of supported SASL security features. 297 - supportedLDAPVersion: LDAP versions implemented by the server. 299 If the server does not master entries and does not know the locations 300 of schema information, the subschemaSubentry attribute is not present 301 in the root DSE. If the server masters directory entries under one or 302 more schema rules, there may be any number of values of the 303 subschemaSubentry attribute in the root DSE. 305 4. Elements of Protocol 307 The LDAP protocol is described using Abstract Syntax Notation 1 308 (ASN.1) [3], and is typically transferred using a subset of ASN.1 309 Basic Encoding Rules [11]. In order to support future extensions to 310 this protocol, clients and servers MUST ignore elements of SEQUENCEs 311 whose tags they do not recognize. 313 Note that unlike X.500, each change to the LDAP protocol other than 314 through the extension mechanisms will have a different version 315 number. A client will indicate the version it supports as part of 316 the bind request, described in section 4.2. If a client has not sent 317 a bind, the server MUST assume that version 3 is supported in the 318 client (since version 2 required that the client bind first). 320 Clients may determine the protocol version a server supports by 321 reading the supportedLDAPVersion attribute from the root DSE. 322 Servers which implement version 3 or later versions MUST provide this 323 attribute. Servers which only implement version 2 may not provide 324 this attribute. 326 4.1. Common Elements 328 This section describes the LDAPMessage envelope PDU (Protocol Data 329 Unit) format, as well as data type definitions which are used in the 330 protocol operations. 332 4.1.1. Message Envelope 334 For the purposes of protocol exchanges, all protocol operations are 335 encapsulated in a common envelope, the LDAPMessage, which is defined 336 as follows: 338 LDAPMessage ::= SEQUENCE { 339 messageID MessageID, 340 protocolOp CHOICE { 341 bindRequest BindRequest, 342 bindResponse BindResponse, 343 unbindRequest UnbindRequest, 344 searchRequest SearchRequest, 345 searchResEntry SearchResultEntry, 346 searchResDone SearchResultDone, 347 searchResRef SearchResultReference, 348 modifyRequest ModifyRequest, 349 modifyResponse ModifyResponse, 350 addRequest AddRequest, 351 addResponse AddResponse, 352 delRequest DelRequest, 353 delResponse DelResponse, 354 modDNRequest ModifyDNRequest, 355 modDNResponse ModifyDNResponse, 356 compareRequest CompareRequest, 357 compareResponse CompareResponse, 358 abandonRequest AbandonRequest, 359 extendedReq ExtendedRequest, 360 extendedResp ExtendedResponse }, 361 controls [0] Controls OPTIONAL } 363 MessageID ::= INTEGER (0 .. maxInt) 365 maxInt INTEGER ::= 2147483647 -- (2^^31 - 1) -- 367 The function of the LDAPMessage is to provide an envelope containing 368 common fields required in all protocol exchanges. At this time the 369 only common fields are the message ID and the controls. 371 If the server receives a PDU from the client in which the LDAPMessage 372 SEQUENCE tag cannot be recognized, the messageID cannot be parsed, 373 the tag of the protocolOp is not recognized as a request, or the 374 encoding structures or lengths of data fields are found to be 375 incorrect, then the server MUST return the notice of disconnection 376 described in section 4.4.1, with resultCode protocolError, and 377 immediately close the connection. In other cases that the server 378 cannot parse the request received by the client, the server MUST 379 return an appropriate response to the request, with the resultCode 380 set to protocolError. 382 If the client receives a PDU from the server which cannot be parsed, 383 the client may discard the PDU, or may abruptly close the connection. 385 The ASN.1 type Controls is defined in section 4.1.12. 387 4.1.1.1. Message ID 389 All LDAPMessage envelopes encapsulating responses contain the 390 messageID value of the corresponding request LDAPMessage. 392 The message ID of a request MUST have a value different from the 393 values of any other requests outstanding in the LDAP session of which 394 this message is a part. 396 A client MUST NOT send a second request with the same message ID as 397 an earlier request on the same connection if the client has not 398 received the final response from the earlier request. Otherwise the 399 behavior is undefined. Typical clients increment a counter for each 400 request. 402 A client MUST NOT reuse the message id of an abandonRequest or of the 403 abandoned operation until it has received a response from the server 404 for another request invoked subsequent to the abandonRequest, as the 405 abandonRequest itself does not have a response. 407 4.1.2. String Types 409 The LDAPString is a notational convenience to indicate that, although 410 strings of LDAPString type encode as OCTET STRING types, the ISO 10646 411 [13] character set (a superset of Unicode) is used, encoded following 412 the UTF-8 algorithm [14]. Note that in the UTF-8 algorithm characters 413 which are the same as ASCII (0x0000 through 0x007F) are represented 414 as that same ASCII character in a single byte. The other byte values 415 are used to form a variable-length encoding of an arbitrary character. 417 LDAPString ::= OCTET STRING 419 The LDAPOID is a notational convenience to indicate that the permitted 420 value of this string is a (UTF-8 encoded) dotted-decimal 421 representation of an OBJECT IDENTIFIER. 423 LDAPOID ::= OCTET STRING 425 For example, 427 1.3.6.1.4.1.1466.1.2.3 429 4.1.3. Distinguished Name and Relative Distinguished Name 431 An LDAPDN and a RelativeLDAPDN are respectively defined to be the 432 representation of a Distinguished Name and a Relative Distinguished 433 Name after encoding according to the specification in [4], such that 435 ::= 437 ::= 439 where and are as defined in [4]. 441 LDAPDN ::= LDAPString 443 RelativeLDAPDN ::= LDAPString 445 Only Attribute Types can be present in a relative distinguished name 446 component; the options of Attribute Descriptions (next section) 447 MUST NOT be used in specifying distinguished names. 449 4.1.4. Attribute Type 451 An AttributeType takes on as its value the textual string associated 452 with that AttributeType in its specification. 454 AttributeType ::= LDAPString 456 Each attribute type has a unique OBJECT IDENTIFIER which has been 457 assigned to it. This identifier may be written as decimal digits 458 with components separated by periods, e.g. "2.5.4.10". 460 A specification may also assign one or more textual names for an 461 attribute type. These names MUST begin with a letter, and only 462 contain ASCII letters, digit characters and hyphens. They are case 463 insensitive. (These ASCII characters are identical to ISO 10646 464 characters whose UTF-8 encoding is a single byte between 0x00 and 465 0x7F.) 467 If the server has a textual name for an attribute type, it MUST use 468 that name for attributes returned in search results. The dotted- 469 decimal OBJECT IDENTIFIER is only used if there is no textual name 470 for an attribute type. 472 Attribute type names are non-unique, as two different specifications 473 (neither in standards track RFCs) may choose the same name. 475 A server which masters or shadows entries SHOULD list all the 476 attribute types it supports in the subschema entries, using the 477 attributeTypes attribute. Servers which support an open-ended set of 478 attributes SHOULD include at least the attributeTypes value for the 479 'objectClass' attribute. Clients MAY retrieve the attributeTypes 480 value from subschema entries in order to obtain the OBJECT IDENTIFIER 481 and other information associated with attribute types. 483 Some attribute type names which are used in this version of LDAP are 484 described in [5]. Servers may implement additional attribute types. 486 4.1.5. Attribute Description 488 An AttributeDescription is a superset of the definition of the 489 AttributeType. It has the same ASN.1 definition, but allows 490 additional options to be specified. They are also case insensitive. 492 AttributeDescription ::= LDAPString 494 A value of AttributeDescription is based on the following BNF: 496 ::= [ ";" ] 498 ::=