1.1 Glossary

This document uses the following terms:

abstract type: A type used in this specification whose representation need not be standardized for interoperability because the type's use is internal to the specification. See also concrete type.

access control list (ACL): A list of access control entries (ACEs) that collectively describe the security rules for authorizing access to some resource; for example, an object or set of objects.

Active Directory: A general-purpose network directory service. Active Directory also refers to the Windows implementation of a directory service. Active Directory stores information about a variety of objects in the network. User accounts, computer accounts, groups, and all related credential information used by the Windows implementation of Kerberos are stored in Active Directory. Active Directory is either deployed as Active Directory Domain Services (AD DS) or Active Directory Lightweight Directory Services (AD LDS). [MS-ADTS] describes both forms. For more information, see [MS-AUTHSOD] section 1.1.1.5.2, Lightweight Directory Access Protocol (LDAP) versions 2 and 3, Kerberos, and DNS.

Active Directory Domain Services (AD DS): A directory service (DS) implemented by a domain controller (DC). The DS provides a data store for objects that is distributed across multiple DCs. The DCs interoperate as peers to ensure that a local change to an object replicates correctly across DCs. For more information, see [MS-AUTHSOD] section 1.1.1.5.2 and [MS-ADTS]. For information about product versions, see [MS-ADTS] section 1. See also Active Directory.

Active Directory Lightweight Directory Services (AD LDS): A directory service (DS) implemented by a domain controller (DC). The most significant difference between AD LDS and Active Directory Domain Services (AD DS) is that AD LDS does not host domain naming contexts (domain NCs). A server can host multiple AD LDS DCs. Each DC is an independent AD LDS instance, with its own independent state. AD LDS can be run as an operating system DS or as a directory service provided by a standalone application (Active Directory Application Mode (ADAM)). For more information, see [MS-ADTS]. See also Active Directory.

ancestor object: An object A is an ancestor of object O if there is a directed path from A to O (in other words, A is on the path from O to the root of the tree containing O).

application naming context (application NC): A specific type of naming context (NC), or an instance of that type, that supports only full replicas (no partial replicas). An application NC cannot contain security principal objects in Active Directory Domain Services (AD DS), but can contain security principal objects in Active Lightweight Directory Services (AD LDS). A forest can have zero or more application NCs in either AD DS or AD LDS. An application NC can contain dynamic objects. Application NCs do not appear in the global catalog (GC). The root of an application NC is an object of class domainDNS.

attribute: An identifier for a single or multivalued data element that is associated with a directory object. An object consists of its attributes and their values. For example, cn (common name), street (street address), and mail (email addresses) can all be attributes of a user object. An attribute's schema, including the syntax of its values, is defined in an attributeSchema object.

attribute syntax: Specifies the format and range of permissible values of an attribute. The syntax of an attribute is defined by several attributes on the attributeSchema object, as specified in [MS-ADTS] section 3.1.1.2. Attribute syntaxes supported by Active Directory include Boolean, Enumeration, Integer, LargeInteger, String(UTC-Time), Object(DS-DN), and String(Unicode).

authentication: The ability of one entity to determine the identity of another entity.

authentication level: A numeric value indicating the level of authentication or message protection that remote procedure call (RPC) will apply to a specific message exchange. For more information, see [C706] section 13.1.2.1 and [MS-RPCE].

binary large object (BLOB): A collection of binary data stored as a single entity in a database.

binary OID: An object identifier (OID) in a Basic Encoding Rules (BER)–encoded binary format, as specified in [ITUX690] section 8.19.

built-in principal: A security principal within the built-in domain whose SID is identical in every domain.

canonical name: A syntactic transformation of an Active Directory distinguished name (DN) into something resembling a path that still identifies an object within a forest. DN "cn=Peter Houston, ou=NTDEV, dc=microsoft, dc=com" translates to the canonical name "microsoft.com/NTDEV/Peter Houston", while the DN "dc=microsoft, dc=com" translates to the canonical name "microsoft.com/".

checksum: A value that is the summation of a byte stream. By comparing the checksums computed from a data item at two different times, one can quickly assess whether the data items are identical.

child object, children: An object that is not the root of its tree. The children of an object o are the set of all objects whose parent is o. See section 1 of [MS-ADTS] and section 1 of [MS-DRSR].

class: See object class.

compression chunk: Portions of replication data that occur when compression is used for that data. Compression chunks are created by dividing the replication data into smaller units that are suitable for the particular algorithm. The chunk size is specific to the compression algorithm being employed.

computer object: An object of class computer. A computer object is a security principal object; the principal is the operating system running on the computer. The shared secret allows the operating system running on the computer to authenticate itself independently of any user running on the system. See security principal.

concrete type: A type used in this specification whose representation must be standardized for interoperability. Specific cases include types in the IDL definition of an RPC interface, types sent over RPC but whose representation is unknown to RPC, and types stored as byte strings in directory attributes.

configuration naming context (config NC): A specific type of naming context (NC), or an instance of that type, that contains configuration information. In Active Directory, a single config NC is shared among all domain controllers (DCs) in the forest. A config NC cannot contain security principal objects.

constructed attribute: An attribute whose values are computed from normal attributes (for read) and/or have effects on the values of normal attributes (for write).

container: An object in the directory that can serve as the parent for other objects. In the absence of schema constraints, all objects would be containers. The schema allows only objects of specific classes to be containers.

control access right: An extended access right that can be granted or denied on an access control list (ACL).

critical object: A subset of the objects in the default naming context (NC), identified by the attribute isCriticalSystemObject having the value TRUE. The objects that are marked in this way are essential for the operation of a domain controller (DC) hosting the NC.

crossRef object: An object residing in the partitions container of the config NC that describes the properties of a naming context (NC), such as its domain naming service name, operational settings, and so on.

cyclic redundancy check (CRC): An algorithm used to produce a checksum (a small, fixed number of bits) against a block of data, such as a packet of network traffic or a block of a computer file. The CRC is a broad class of functions used to detect errors after transmission or storage. A CRC is designed to catch random errors, as opposed to intentional errors. If errors might be introduced by a motivated and intelligent adversary, a cryptographic hash function should be used instead.

default naming context (default NC): When Active Directory is operating as Active Directory Domain Services (AD DS), the default naming context (default NC) is the domain naming context (domain NC) whose full replica is hosted by a domain controller (DC), except when the DC is a read-only domain controller (RODC), in which case the default NC is a filtered partial NC replica. When operating as AD DS, a DC's default NC is the NC of its default NC replica, and the default NC contains the DC's computer object. When Active Directory is operating as AD LDS, the default NC is the naming context (NC) specified by the msDS-DefaultNamingContext attribute on the nTDSDSA object for the DC. See nTDSDSA object.

deleted-object: An object that has been deleted, but remains in storage until a configured amount of time (the deleted-object lifetime) has passed, after which the object is transformed to a recycled-object. Unlike a recycled-object or a tombstone, a deleted-object maintains virtually all the state of the object before deletion, and can be undeleted without loss of information. Deleted-objects exist only when the Recycle Bin optional feature is enabled.

digest: The fixed-length output string from a one-way hash function that takes a variable-length input string and is probabilistically unique for every different input string. Also, a cryptographic checksum of a data (octet) stream.

directory: The database that stores information about objects such as users, groups, computers, printers, and the directory service that makes this information available to users and applications.

directory object: An Active Directory object, which is a specialization of the "object" concept that is described in [MS-ADTS] section 1 or [MS-DRSR] section 1, Introduction, under Pervasive Concepts. An Active Directory object can be identified by the objectGUID attribute of a dsname according to the matching rules defined in [MS-DRSR] section 5.50, DSNAME. The parent-identifying attribute (not exposed as an LDAP attribute) is parent. Active Directory objects are similar to LDAP entries, as defined in [RFC2251]; the differences are specified in [MS-ADTS] section 3.1.1.3.1.

directory service agent (DSA): A term from the X.500 directory specification [X501] that represents a component that maintains and communicates directory information.

distinguished name (DN): In Lightweight Directory Access Protocol (LDAP), an LDAP Distinguished Name, as described in [RFC2251] section 4.1.3. The DN of an object is the DN of its parent, preceded by the RDN of the object. For example: CN=David Thompson, OU=Users, DC=Microsoft, DC=COM. For definitions of CN and OU, see [RFC2256] sections 5.4 and 5.12, respectively.

domain: A set of users and computers sharing a common namespace and management infrastructure. At least one computer member of the set must act as a domain controller (DC) and host a member list that identifies all members of the domain, as well as optionally hosting the Active Directory service. The domain controller provides authentication of members, creating a unit of trust for its members. Each domain has an identifier that is shared among its members. For more information, see [MS-AUTHSOD] section 1.1.1.5 and [MS-ADTS].

domain controller (DC): The service, running on a server, that implements Active Directory, or the server hosting this service. The service hosts the data store for objects and interoperates with other DCs to ensure that a local change to an object replicates correctly across all DCs. When Active Directory is operating as Active Directory Domain Services (AD DS), the DC contains full NC replicas of the configuration naming context (config NC), schema naming context (schema NC), and one of the domain NCs in its forest. If the AD DS DC is a global catalog server (GC server), it contains partial NC replicas of the remaining domain NCs in its forest. For more information, see [MS-AUTHSOD] section 1.1.1.5.2 and [MS-ADTS]. When Active Directory is operating as Active Directory Lightweight Directory Services (AD LDS), several AD LDS DCs can run on one server. When Active Directory is operating as AD DS, only one AD DS DC can run on one server. However, several AD LDS DCs can coexist with one AD DS DC on one server. The AD LDS DC contains full NC replicas of the config NC and the schema NC in its forest. The domain controller is the server side of Authentication Protocol Domain Support [MS-APDS].

domain name: A domain name or a NetBIOS name that identifies a domain.

domain naming context (domain NC): A specific type of naming context (NC), or an instance of that type, that represents a domain. A domain NC can contain security principal objects; no other type of NC can contain security principal objects. Domain NCs appear in the global catalog (GC). A domain NC is hosted by one or more domain controllers (DCs) operating as AD DS. In AD DS, a forest has one or more domain NCs. A domain NC cannot exist in AD LDS. The root of a domain NC is an object of class domainDNS; for directory replication [MS-DRSR], see domainDNS.

domain security identifier (domain SID): The SID of the root object of a domain NC. The relative identifier (RID) portion of the domain SID is always zero. Every security principal object in a domain NC has an objectSid attribute equal to the domain SID except for the RID portion.

domainDNS: A specific object class. The root of a domain NC or an application NC is an object of class domainDNS. The DN of such an object takes the form  dc=n1,dc=n2, ... dc=nk, where each ni satisfies the syntactic requirements of a fully qualified domain name (FQDN) component (for more information, see [RFC1034]). Such a DN corresponds to the FQDN n1.n2. ... .nk. This is the FQDN of the NC, and it allows replicas of the NC to be located by using DNS.

DSA GUID: The objectGUID of a DSA object.

dsname: A tuple that contains between one and three identifiers for an object. The term dsname does not stand for anything. The possible identifiers are the object's GUID (attribute objectGuid), security identifier (SID) (attribute objectSid), and distinguished name (DN) (attribute distinguishedName). A dsname can appear in a protocol message and as an attribute value (for example, a value of an attribute with syntax Object(DS-DN)). Given a DSName, an object can be identified within a set of NC replicas according to the matching rules defined in [MS-DRSR] section 5.49.

dynamic endpoint: A network-specific server address that is requested and assigned at run time. For more information, see [C706].

dynamic object: An object with a time-to-die (attribute msDS-Entry-Time-To-Die). The directory service garbage-collects a dynamic object immediately after its time-to-die has passed. The constructed attribute entryTTL gives a dynamic object's current time-to-live, that is, the difference between the current time and msDS-Entry-Time-To-Die. For more information, see [RFC2589].

endpoint: A network-specific address of a remote procedure call (RPC) server process for remote procedure calls. The actual name and type of the endpoint depends on the RPC protocol sequence that is being used. For example, for RPC over TCP (RPC Protocol Sequence ncacn_ip_tcp), an endpoint might be TCP port 1025. For RPC over Server Message Block (RPC Protocol Sequence ncacn_np), an endpoint might be the name of a named pipe. For more information, see [C706].

expunge: To permanently remove an object from a naming context (NC) replica, without converting it to a tombstone.

extended canonical name: Same as a canonical name, except that the rightmost forward slash ('/') is replaced with a newline character.

extended operation: A special replication cycle in which a client DC requests an action on a FSMO role; for example, a change in the FSMO role owner. FSMO role abandon and FSMO role transfer are examples of extended operations.

filtered attribute set: The subset of attributes that are not replicated to the filtered partial NC replica and the filtered GC partial NC replica. The filtered attribute set is part of the state of the forest and is used to control the attributes that replicate to a read-only domain controller (RODC). The searchFlags schema attribute is used to define this set.

flexible single master operation (FSMO): A read or update operation on a naming context (NC), such that the operation must be performed on the single designated master replica of that NC. The master replica designation is "flexible" because it can be changed without losing the consistency gained from having a single master. This term, pronounced "fizmo", is never used alone; see also FSMO role, FSMO role owner, and FSMO object.

forest: For Active Directory Domain Services (AD DS), a set of naming contexts (NCs) consisting of one schema naming context (schema NC), one configuration naming context (config NC), one or more domain naming contexts (domain NCs), and zero or more application naming contexts (application NCs). Because a set of NCs can be arranged into a tree structure, a forest is also a set containing one or several trees of NCs. For AD LDS, a set of NCs consisting of one schema NC, one config NC, and zero or more application NCs. (In Microsoft documentation, an AD LDS forest is called a "configuration set".)

forest root domain NC: For Active Directory Domain Services (AD DS), the domain naming context (domain NC) within a forest whose child is the forest's configuration naming context (config NC). The fully qualified domain name (FQDN) of the forest root domain NC serves as the forest's name.

forward link attribute: An attribute whose values include object references (for example, an attribute of syntax Object(DS-DN)). The forward link values can be used to compute the values of a related attribute, a back link attribute, on other objects. If an object o refers to object r in forward link attribute f, and there exists a back link attribute b corresponding to f, then a back link value referring to o exists in attribute b on object r. The relationship between the forward and back link attributes is expressed using the linkId attribute on the attributeSchema objects representing the two attributes. The forward link's linkId is an even number, and the back link's linkId is the forward link's linkId plus one. A forward link attribute can exist with no corresponding back link attribute, but not vice-versa. For more information, see [MS-ADTS].

FSMO role: A set of objects that can be updated in only one naming context (NC) replica (the FSMO role owner's replica) at any given time. For more information, see [MS-ADTS] section 3.1.1.1.11. See also FSMO role owner.

FSMO role object: An object in a directory that represents a specific FSMO role. This object is an element of the FSMO role and contains the fSMORoleOwner attribute.

FSMO role owner: The domain controller (DC) holding the naming context (NC) replica in which the objects of a FSMO role can be updated.

full NC replica: A naming context (NC) replica that contains all the attributes of the objects it contains. A full replica accepts originating updates.

fully qualified domain name (FQDN): (1) An unambiguous domain name that gives an absolute location in the Domain Name System's (DNS) hierarchy tree, as defined in [RFC1035] section 3.1 and [RFC2181] section 11.

(2) In Active Directory, a fully qualified domain name (FQDN) (1) that identifies a domain.

GC partial attribute set (PAS): The subset of attributes that replicate to a GC partial NC replica. A particular GC partial attribute set (PAS) is part of the state of the forest and is used to control the attributes that replicate to global catalog servers (GC servers). The isMemberOfPartialAttributeSet schema attribute is used to define this set.

global catalog (GC): A unified partial view of multiple naming contexts (NCs) in a distributed partitioned directory. The Active Directory directory service GC is implemented by GC servers. The definition of global catalog is specified in [MS-ADTS] section 3.1.1.1.8.

global catalog server (GC server): A domain controller (DC) that contains a naming context (NC) replica (one full, the rest partial) for each domain naming context in the forest.

global group: An Active Directory group that allows user objects from its own domain and global groups from its own domain as members. Also called domain global group. Universal groups can contain global groups. A group object g is a global group if and only if GROUP_TYPE_ACCOUNT_GROUP is present in g! groupType; see [MS-ADTS] section 2.2.12, "Group Type Flags". A global group that is also a security-enabled group is valid for inclusion within ACLs anywhere in the forest. If a domain is in mixed mode, then a global group in that domain that is also a security-enabled group allows only user object as members. See also domain local group, security-enabled group.

globally unique identifier (GUID): A term used interchangeably with universally unique identifier (UUID) in Microsoft protocol technical documents (TDs). Interchanging the usage of these terms does not imply or require a specific algorithm or mechanism to generate the value. Specifically, the use of this term does not imply or require that the algorithms described in [RFC4122] or [C706] must be used for generating the GUID. See also universally unique identifier (UUID).

group: A group object.

group object: In Active Directory, a group object has an object class group. A group has a forward link attribute member; the values of this attribute either represent elements of the group (for example, objects of class user or computer) or subsets of the group (objects of class group). The representation of group subsets is called "nested group membership". The back link attribute memberOf enables navigation from group members to the groups containing them. Some groups represent groups of security principals and some do not and are, for instance, used to represent email distribution lists.

Interface Definition Language (IDL): The International Standards Organization (ISO) standard language for specifying the interface for remote procedure calls. For more information, see [C706] section 4.

Internet host name: The name of a host as defined in [RFC1123] section 2.1, with the extensions described in [MS-HNDS].

invocation ID: The invocationId attribute. An attribute of an nTDSDSA object. Its value is a unique identifier for a function that maps from update sequence numbers (USNs) to updates to the  NC replicas of a domain controller (DC). See also nTDSDSA object.

Knowledge Consistency Checker (KCC): A component of the Active Directory replication that is used to create spanning trees for domain controller to domain controller replication and to translate those trees into settings of variables that implement the replication topology.

LDAP connection: A TCP connection from a client to a server over which the client sends Lightweight Directory Access Protocol (LDAP) requests and the server sends responses to the client's requests.

Lightweight Directory Access Protocol (LDAP): The primary access protocol for Active Directory. Lightweight Directory Access Protocol (LDAP) is an industry-standard protocol, established by the Internet Engineering Task Force (IETF), which allows users to query and update information in a directory service (DS), as described in [MS-ADTS]. The Lightweight Directory Access Protocol can be either version 2 [RFC1777] or version 3 [RFC3377].

lingering object: An object that still exists in an NC replica even though it has been deleted and garbage-collected from other replicas. This occurs, for instance, when a domain controller (DC) goes offline for longer than the tombstone lifetime.

link attribute: A forward link attribute or a back link attribute.

link value: The value of a link attribute.

link value stamp: The type of a stamp attached to a link value.

local domain controller (local DC): A domain controller (DC) on which the current method is executing.

Lost and Found container: A container holding objects in a given naming context (NC) that do not have parent objects due to add and remove operations that originated on different domain controllers (DCs). The container is a child of the NC root and has RDN CN=LostAndFound in domain NCs and CN=LostAndFoundConfig in config NCs.

Microsoft Interface Definition Language (MIDL): The Microsoft implementation and extension of the OSF-DCE Interface Definition Language (IDL). MIDL can also mean the Interface Definition Language (IDL) compiler provided by Microsoft. For more information, see [MS-RPCE].

MSZIP compression algorithm: A compression algorithm specified in [RFC1951] that is used between Windows 2000 operating system DCs.

naming context (NC): An NC is a set of objects organized as a tree. It is referenced by a DSName. The DN of the DSName is the distinguishedName attribute of the tree root. The GUID of the DSName is the objectGUID attribute of the tree root. The security identifier (SID) of the DSName, if present, is the objectSid attribute of the tree root; for Active Directory Domain Services (AD DS), the SID is present if and only if the NC is a domain naming context (domain NC). Active Directory supports organizing several NCs into a tree structure.

NC replica: A variable containing a tree of objects whose root object is identified by some naming context (NC).

NetBIOS domain name: The name registered by domain controllers (DCs) on [1C] records of the NBNS (WINS) server (see section 6.3.4). For details of NetBIOS name registration, see [MS-WPO] sections 7.1.4 and 10.4.

nonreplicated attribute: An attribute whose values are not replicated between naming context (NC) replicas. The nonreplicated attributes of an object are, in effect, local variables of the domain controller (DC) hosting the NC replica containing that object, since changes to these attributes have no effect outside that DC.

nTDSDSA object: An object of class nTDSDSA that is always located in the configuration naming context (config NC). This object represents a domain controller (DC) in the forest. See [MS-ADTS] section 6.1.1.2.2.1.2.1.1.

NULL GUID: A GUID of all zeros.

object: A set of attributes, each with its associated values. For more information on objects, see [MS-ADTS] section 1 or [MS-DRSR] section 1.

object class: A set of restrictions on the construction and update of objects. An object class can specify a set of must-have attributes (every object of the class must have at least one value of each) and may-have attributes (every object of the class may have a value of each). An object class can also specify the allowable classes for the parent object of an object in the class. An object class can be defined by single inheritance; an object whose class is defined in this way is a member of all object classes used to derive its most specific class. An object class is defined in a classSchema object. See section 1 of [MS-ADTS] and section 1 of [MS-DRSR].

object identifier (OID): In the Lightweight Directory Access Protocol (LDAP), a sequence of numbers in a format described by [RFC1778]. In many LDAP directory implementations, an OID is the standard internal representation of an attribute. In the directory model used in this specification, the more familiar ldapDisplayName represents an attribute.

object of class x (or x object): An object o such that one of the values of its objectClass attributes is x. For instance, if objectClass contains the value user,  o is an object of class user. This is often contracted to "user object".

object reference: An attribute value that references an object. Reading a reference gives the distinguished name (DN) of the object.

objectClass: The objectClass attribute. The attribute on an object that holds the object class name of each object class of the object.

objectGUID: The attribute on an Active Directory object whose value is a GUID that uniquely identifies the object. The GUID value of an object's objectGUID is assigned when the object was created and is immutable thereafter. The integrity of object references between NCs and of replication depends on the integrity of the objectGUID attribute. For a descrption of the general concept of an "object", see [MS-ADTS] section 1. For more detailed information see [MS-ADTS] section 3.1.1.1.3.

objectSid: The objectSid attribute. The attribute on an object whose value is a SID that identifies the object as a security principal object. The value of an object's objectSid is assigned when the security principal object was created and is immutable thereafter unless the object moves to another domain. The integrity of authentication depends on the integrity of the objectSid attribute.

opnum: An operation number or numeric identifier that is used to identify a specific remote procedure call (RPC) method or a method in an interface. For more information, see [C706] section 12.5.2.12 or [MS-RPCE].

optional feature: A non-default behavior that modifies the Active Directory state model. An optional feature is enabled or disabled in a specific scope, such as a forest or a domain. For more information, refer to [MS-ADTS] section 3.1.1.9.

oriented tree: A directed acyclic graph such that for every vertex v, except one (the root), there is a unique edge whose tail is v. There is no edge whose tail is the root. For more information, see [KNUTH1] section 2.3.4.2.

originating update: An update that is performed to an NC replica via any protocol except replication. An originating update to an attribute or link value generates a new stamp for the attribute or link value.

parent object: An object is either the root of a tree of objects or has a parent. If two objects have the same parent, they must have different values in their relative distinguished names (RDNs). See also, object in section 1 of [MS-ADTS] and section 1 of [MS-DRSR].

partial attribute set (PAS): The subset of attributes that replicate to partial naming context (NC) replicas. Also, the particular partial attribute set that is part of the state of a forest and that is used to control the attributes that replicate to global catalog (GC) servers.

partial NC replica: An NC replica that contains a schema-specified subset of attributes for the objects it contains. A partial NC replica is not writable—it does not accept originating updates. See also writable NC replica.

Partitions container: A child object of the configuration naming context (config NC) root. The relative distinguished name (RDN) of the Partitions container is "cn=Partitions" and its class is crossRefContainer ([MS-ADTS] section 2.30). See also crossRef object.

PDC emulator: A DC that is designated to track changes made to the accounts of all computers in a domain. The PDC emulator is the only computer to receive these changes directly and is specialized so as to ensure consistency and to eliminate the potential for conflicting entries in the Active Directory database. A domain has only one PDC emulator.

prefix table: A data structure that is used to translate between an object identifier (OID) and a compressed representation for OIDs. See [MS-DRSR] section 5.14.

primary domain controller (PDC): A domain controller (DC) designated to track changes made to the accounts of all computers on a domain. It is the only computer to receive these changes directly, and is specialized so as to ensure consistency and to eliminate the potential for conflicting entries in the Active Directory database. A domain has only one PDC.

primary domain controller (PDC) role owner: The domain controller (DC) that hosts the primary domain controller emulator FSMO role for a given domain naming context (NC).

principal: See security principal.

Privileged Access Management: An optional feature that enables the removal of a link value from the state of a domain controller (DC) at a specified date and time.

read permission: The authorization to read an attribute of an object. For more information, see [MS-ADTS] section 5.1.3.

read-only domain controller (RODC): A domain controller (DC) that does not accept originating updates. Additionally, an RODC does not perform outbound replication. An RODC cannot be the primary domain controller (PDC) for its domain.

Recycle Bin: An optional feature that modifies the state model of object deletions and undeletions, making undeletion of deleted-objects possible without loss of the object's attribute values. For more information, see [MS-ADTS] section 3.1.1.9.1.

recycled-object: An object that has been deleted, but remains in storage until a configured amount of time (the tombstone lifetime) has passed, after which the object is permanently removed from storage. Unlike a deleted-object, most of the state of the object has been removed, and the object can no longer be undeleted without loss of information. By keeping the recycled-object in existence for the tombstone lifetime, the deleted state of the object is able to replicate. Recycled-objects exist only when the Recycle Bin optional feature is enabled.

relative distinguished name (RDN): The name of an object relative to its parent. This is the leftmost attribute-value pair in the distinguished name (DN) of an object. For example, in the DN "cn=Peter Houston, ou=NTDEV, dc=microsoft, dc=com", the RDN is "cn=Peter Houston". For more information, see [RFC2251].

relative identifier (RID): The last item in the series of SubAuthority values in a security identifier (SID) [SIDD]. It distinguishes one account or group from all other accounts and groups in the domain. No two accounts or groups in any domain share the same RID.

remote procedure call (RPC): A context-dependent term commonly overloaded with three meanings. Note that much of the industry literature concerning RPC technologies uses this term interchangeably for any of the three meanings. Following are the three definitions: (*) The runtime environment providing remote procedure call facilities. The preferred usage for this meaning is "RPC runtime". (*) The pattern of request and response message exchange between two parties (typically, a client and a server). The preferred usage for this meaning is "RPC exchange". (*) A single message from an exchange as defined in the previous definition. The preferred usage for this term is "RPC message". For more information about RPC, see [C706].

replica: A variable containing a set of objects.

replicated attribute: An attribute whose values are replicated to other NC replicas. An attribute is replicated if its attributeSchema object o does not have a value for the systemFlags attribute, or if the FLAG_ATTR_NOT_REPLICATED bit (bit 0) of o! systemFlags is zero.

replicated update: An update performed to a naming context (NC) replica by the replication system, to propagate the effect of an originating update at another NC replica. The stamp assigned during the originating update to attribute values or a link value is preserved by replication.

replication: The process of propagating the effects of all originating writes to any replica of a naming context (NC), to all replicas of the NC. If originating writes cease and replication continues, all replicas converge to a common application-visible state.

replication cycle: Sometimes referred to simply as "cycle". A series of one or more replication responses associated with the same invocationId, concluding with the return of a new up-to-date vector.

replication epoch: A state variable of a DC that changes when a DC is no longer compatible for replication with its former partners. A server receiving a replication request tests the client's replication epoch against its own, and refuses the request if the two are not equal.

replication latency: The time lag between a final originating update to a naming context (NC) replica and all NC replicas reaching a common application-visible state.

RPC protocol sequence: A character string that represents a valid combination of a remote procedure call (RPC) protocol, a network layer protocol, and a transport layer protocol, as described in [C706] and [MS-RPCE].

RPC transport: The underlying network services used by the remote procedure call (RPC) runtime for communications between network nodes. For more information, see [C706] section 2.

schema: The set of attributes and object classes that govern the creation and update of objects.

schema naming context (schema NC): A specific type of naming context (NC) or an instance of that type. A forest has a single schema NC, which is replicated to each domain controller (DC) in the forest. No other NC replicas can contain these objects. Each attribute and class in the forest's schema is represented as a corresponding object in the forest's schema NC. A schema NC cannot contain security principal objects.

secret data: An implementation-specific set of attributes on objects of class user that contain security-sensitive information about the security principal.

security context: A data structure containing authorization information for a particular security principal in the form of a collection of security identifiers (SIDs). One SID identifies the principal specifically, whereas others represent other capabilities. A server uses the authorization information in a security context to check access to requested resources.

security descriptor: A data structure containing the security information associated with a securable object. A security descriptor identifies an object's owner by its security identifier (SID). If access control is configured for the object, its security descriptor contains a discretionary access control list (DACL) with SIDs for the security principals who are allowed or denied access. Applications use this structure to set and query an object's security status. The security descriptor is used to guard access to an object as well as to control which type of auditing takes place when the object is accessed. The security descriptor format is specified in [MS-DTYP] section 2.4.6; a string representation of security descriptors, called SDDL, is specified in [MS-DTYP] section 2.5.1.

security identifier (SID): An identifier for security principals that is used to identify an account or a group. Conceptually, the SID is composed of an account authority portion (typically a domain) and a smaller integer representing an identity relative to the account authority, termed the relative identifier (RID). The SID format is specified in [MS-DTYP] section 2.4.2; a string representation of SIDs is specified in [MS-DTYP] section 2.4.2 and [MS-AZOD] section 1.1.1.2.

security principal: A unique entity, also referred to as a principal, that can be authenticated by Active Directory. It frequently corresponds to a human user, but also can be a service that offers a resource to other security principals. Other security principals might be a group, which is a set of principals. Groups are supported by Active Directory.

security provider: A pluggable security module that is specified by the protocol layer above the remote procedure call (RPC) layer, and will cause the RPC layer to use this module to secure messages in a communication session with the server. The security provider is sometimes referred to as an authentication service. For more information, see [C706] and [MS-RPCE].

server object: A class of object in the configuration naming context (config NC). A server object can have an nTDSDSA object as a child.

service account: A stored set of attributes that represent a principal that provides a security context for services.

service class: The first part of a service principal name. See [MS-KILE] section 3.1.5.11.

service principal name (SPN): The name a client uses to identify a service for mutual authentication. (For more information, see [RFC1964] section 2.1.1.) An SPN consists of either two parts or three parts, each separated by a forward slash ('/'). The first part is the service class, the second part is the host name, and the third part (if present) is the service name. For example, "ldap/dc-01.fabrikam.com/fabrikam.com" is a three-part SPN where "ldap" is the service class name, "dc-01.fabrikam.com" is the host name, and "fabrikam.com" is the service name. See [SPNNAMES] for more information about SPN format and composing a unique SPN.

session key: A relatively short-lived symmetric key (a cryptographic key negotiated by the client and the server based on a shared secret). A session key's lifespan is bounded by the session to which it is associated. A session key has to be strong enough to withstand cryptanalysis for the lifespan of the session.

SHA1 hash: A hashing algorithm defined in [FIPS180] that was developed by the National Institute of Standards and Technology (NIST) and the National Security Agency (NSA).

site: A collection of one or more well-connected (reliable and fast) TCP/IP subnets. By defining sites (represented by site objects) an administrator can optimize both Active Directory access and Active Directory replication with respect to the physical network. When users log in, Active Directory clients find domain controllers (DCs) that are in the same site as the user, or near the same site if there is no DC in the site. See also Knowledge Consistency Checker (KCC). For more information, see [MS-ADTS].

site object: An object of class site, representing a site.

stamp: Information that describes an originating update by a domain controller (DC). The stamp is not the new data value; the stamp is information about the update that created the new data value. A stamp is often called metadata, because it is additional information that "talks about" the conventional data values. A stamp contains the following pieces of information: the unique identifier of the DC that made the originating update; a sequence number characterizing the order of this change relative to other changes made at the originating DC; a version number identifying the number of times the data value has been modified; and the time when the change occurred.

STATUS code: A 32-bit quantity where zero represents success and nonzero represents failure. The specific failure codes used in this specification are Windows error codes.

subordinate reference object (sub-ref object): The naming context (NC) root of a parent NC has a list of all the NC roots of its child NCs in the subRefs attribute ([MS-ADA3] section 2.282). Each entry in this list is a subordinate reference and the object named by the entry is denominated a subordinate reference object. An object is a subordinate reference object if and only if it is in such a list. If a server has replicas of both an NC and its child NC, then the child NC root is the subordinate reference object, in the context of the parent NC. If the server does not have a replica of the child NC, then another object, with distinguishedName ([MS-ADA1] section 2.177) and objectGUID ([MS-ADA3] section 2.44) attributes equal to the child NC root, is present in the server and is the subordinate reference object.

target object: An object referenced by a forward link value.

tombstone: An object that has been deleted, but remains in storage until a configured amount of time (the tombstone lifetime) has passed, after which the object is permanently removed from storage. By keeping the tombstone in existence for the tombstone lifetime, the deleted state of the object is able to replicate. Tombstones exist only when the Recycle Bin optional feature is not enabled.

Unicode: A character encoding standard developed by the Unicode Consortium that represents almost all of the written languages of the world. The Unicode standard [UNICODE5.0.0/2007] provides three forms (UTF-8, UTF-16, and UTF-32) and seven schemes (UTF-8, UTF-16, UTF-16 BE, UTF-16 LE, UTF-32, UTF-32 LE, and UTF-32 BE).

universal group: An Active Directory group that allows user objects, global groups, and universal groups from anywhere in the forest as members. A group object g is a universal group if and only if GROUP_TYPE_UNIVERSAL_GROUP is present in g! groupType. A security-enabled universal group is valid for inclusion within ACLs anywhere in the forest. If a domain is in mixed mode, then a universal group cannot be created in that domain. See also domain local group, security-enabled group.

universally unique identifier (UUID): A 128-bit value. UUIDs can be used for multiple purposes, from tagging objects with an extremely short lifetime, to reliably identifying very persistent objects in cross-process communication such as client and server interfaces, manager entry-point vectors, and RPC objects. UUIDs are highly likely to be unique. UUIDs are also known as globally unique identifiers (GUIDs) and these terms are used interchangeably in the Microsoft protocol technical documents (TDs). Interchanging the usage of these terms does not imply or require a specific algorithm or mechanism to generate the UUID. Specifically, the use of this term does not imply or require that the algorithms described in [RFC4122] or [C706] must be used for generating the UUID.

update: An add, modify, or delete of one or more objects or attribute values.  See originating update, replicated update.

update sequence number (USN): A monotonically increasing sequence number used in assigning a stamp to an originating update. For more information, see [MS-ADTS].

up-to-date vector: The representation of an assertion about the presence of originating updates from different sources in an NC replica. See replication cycle and update sequence number (USN).

user object: An object of class user. A user object is a security principal object; the principal is a person or service entity running on the computer. The shared secret allows the person or service entity to authenticate itself, as described in ([MS-AUTHSOD] section 1.1.1.1).

Windows error code: A 32-bit quantity where zero represents success and nonzero represents failure. The specific failure codes are specified in [MS-ERREF].

writable naming context (NC) replica: A naming context (NC) replica that accepts originating updates. A writable NC replica is always full, but a full NC replica is not always writable. Partial replicas are not writable. See also read-only full NC replica.

MAY, SHOULD, MUST, SHOULD NOT, MUST NOT: These terms (in all caps) are used as defined in [RFC2119]. All statements of optional behavior use either MAY, SHOULD, or SHOULD NOT.

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