A agenda account has two above features. First, it distributes its advice abject amid abounding altered servers. Second, users can admission agenda advice by querying any of those servers. Making this assignment requires defining a namespace in which anniversary object’s breadth can be bound determined.
As we saw in the aftermost section, advice in an LDAP database comes in the anatomy of objects. Altar accept attributes that call them. For example, the User article for Tom Jones would accept attributes such as Tom’s logon name, his password, his buzz number, his email address, his department, and so forth.
When an LDAP applicant needs to locate advice about an object, it submits a concern that contains the object’s acclaimed name (DN) and the attributes the applicant wants to see. A chase for advice about Tom Jones could be phrased in a brace of ways:
You could chase for attributes in Tom’s User object. “Give me the Administration aspect for cn=Tom Jones,cn=Users,dc=Company,dc=com.”
You could chase for attributes that end up including Tom’s object. “Give me all User altar with a Administration attribute according to Finance.”
In either case, LDAP can acquisition Tom’s article because the name assigned to the article describes its abode in the LDAP namespace.
Figure 6.6 shows a allocation of the LDAP namespace in Active Directory. With one exception, anniversary binder represents a Alembic object, which in about-face holds added objects. The barring is the breadth controllers object, which is an Organizational Unit (OU). Breadth controllers are placed in an OU so that they can accept detached accumulation policies. Generic Alembic altar cannot be affiliated to accumulation policies.
Figure 6.6. Archetype LDAP agenda hierarchy.
The User altar in the diagram accept designators that alpha with CN, acceptation Accepted Name. The CN designator applies to all but a few article types. Active Agenda alone uses two added article designators (although LDAP defines several). They are as follows:
Breadth Basic (DC). DC altar represent the top of an LDAP timberline that uses DNS to ascertain its namespace. Active Agenda is an archetype of such an LDAP tree. The designator for an Active Agenda breadth with the DNS name Company.com would be dc=Company,dc=com.
Organizational Unit (OU). OU altar act as containers that authority added objects. They accommodate anatomy to the LDAP namespace. OUs are the alone general-purpose alembic accessible to administrators in Active Directory. An archetype OU name would be ou=Accounting.
A name that includes an object’s absolute aisle to the basis of the LDAP namespace is alleged its acclaimed name, or DN. An archetype DN for a user alleged CSantana whose article is stored in the cn=Users alembic in a breadth alleged Company.com would be cn=CSantana,cn=Users,dc=Company,dc=com.
An anecdotic appropriate of LDAP acclaimed names is their little-endian aisle syntax. As you apprehend from larboard to right, you biking up the agenda tree. This contrasts to book arrangement paths, which run bottomward the timberline as you apprehend from larboard to right.
An article name after a path, or a fractional path, is alleged a about acclaimed name, or RDN. The accepted name cn=CSantana is an archetype of an RDN. So is cn=CSantana,cn=Users. The RDN serves the aforementioned purpose as a aisle fragment in a filename. It is a acceptable abyssal shortcut.
Two altar can accept the aforementioned RDN, but LDAP has a aphorism that no two altar can accept the aforementioned DN. This makes faculty if you anticipate of the acquisitive attributes of the database. Two altar with the aforementioned DN would try to absorb the aforementioned row in the database table. C’est impossible, as we say in southern New Mexico.
Distinguished names in Active Agenda are not case sensitive. In best instances, the case you specify aback you admission a value is retained in the object’s attribute. This is agnate to the way Windows treats filenames. Feel chargeless to mix cases based on your accumulated standards or claimed aesthetic.
The aggregate of an object’s name and its LDAP designator is alleged a typeful name. Examples accommodate cn=Administrator and cn=Administrator,cn=Users,dc=Company, dc=com.
Some applications can anatomize for delimiters such as periods or semicolons amid the elements of a acclaimed name. For example, an appliance may admittance you to admission Administrator.Users.Company.com rather than the abounding typeful name. This is alleged typeless naming. Aback entering typeless names, it is important to abode the delimiters properly.
The console-based accoutrement provided by Microsoft use a GUI to cross the LDAP namespace, so you don’t charge to anguish about interpreting typeful or typeless names appropriate away. But if you appetite to use many of the abutment accoutrement that appear on the Windows Server 2003 CD or in the Resource Kit, or you appetite to use scripts to manage Active Directory, you’ll charge to use typeful naming. After you get the adhere of it, awkward off a continued typeful name becomes additional nature.
In LDAP, as in X.500, the servers that host copies of the advice abject are alleged Agenda Account Agents, or DSAs. A DSA can host all or allotment of the advice base. The portions of the advice abject anatomy a bureaucracy alleged a Agenda Advice Tree, or DIT. Figure 6.7 shows an example.
Figure 6.7. Agenda Advice Tree.
The top of the DIT is active by a distinct object. The chic of this article is not authentic by the LDAP specification. In Active Directory, the article charge appear from the article chic DomainDNS. Because Active Agenda uses DNS to anatomy its namespace, the DomainDNS article is accustomed a DC designator. For example, the article at the top of the tree in Figure 6.7 would accept the acclaimed name dc=Company,dc=com.
If you address scripts and you charge to acquiesce for periods in article names, announce the aeon with a backslash. This tells the parser that the aeon is a appropriate character, not a delimiter. For example, if your user names attending like tom.collins, a typeless name in a calligraphy would attending like this: tom.collins.Users.Company.com. The aforementioned is accurate for user names that accept anchored commas and periods, such as Winston H. Borntothepurple, Jr. An ADSI concern for this name would attending like this: winston h. borntothepurple, jr.
Active Agenda cannot be abiding at the actual top of a DNS namespace. The acceptance is that abounding altered Active Agenda namespaces could allotment the aforementioned root. For this reason, the DomainDNS article at the top of the timberline charge consistently accept at atomic two breadth basic designators.
An LDAP timberline contains branches formed by containers beneath the basis container. These containers authority altar that accept some relation to anniversary added as authentic by the namespace. For instance, in Active Directory, the absence alembic for User altar is cn=Users. For Computer objects, it is cn=Computers. Advice about accumulation policies, DNS, Remote Admission Services, and so alternating go in cn=System. As we’ll see aback we altercate Active Agenda architecture in Affiliate 8, “Designing Windows Server 2003 Domains,” administrators accept the adeptness to actualize Organizational Units (OUs) to accommodate altar that accept agnate administration or agreement requirements.
As the cardinal of altar in a DIT grows, the database may get too ample to abundance calmly on one DSA. Also, an organization ability appetite to use bandwidth added finer by application a DSA in New York to abundance advice about users in North America and addition DSA in Amsterdam to abundance advice about users in Europe.
X.501, “Information Technology—Open Systems Interconnection—The Directory: Models,” defines the appellation allotment ambience as, “A subtree of entries captivated in a distinct adept DSA.” It goes on to call the action of adding a timberline into assorted naming contexts as partitioning.
Novell chose to accept the appellation allotment to ascertain abstracted pieces of the agenda database. In their seminal book, Understanding and Deploying LDAP Agenda Services, Tim Howe, Mark Smith, and Gordon Good use the appellation allotment in favor of allotment context, although they call both as acceptation the aforementioned thing. Microsoft uses the two agreement interchangeably.
The accoutrement that appear with the Windows Server 2003 CD and in the Resource Kit favor the appellation allotment context. That is the appellation I use throughout this book.
Here is breadth the broadcast attributes of an LDAP database comes into play. The Agenda Advice Abject can be afar into genitalia alleged allotment contexts, or NCs. In Active Directory, anniversary breadth represents a abstracted allotment context. Breadth controllers in the aforementioned breadth each accept a read/write replica of that Breadth allotment context. Agreement and Schema altar are stored in their own allotment contexts, as are DNS Record altar aback application Active Agenda Integrated DNS zones.
When a applicant submits a concern for advice about a accurate object, the arrangement charge actuate which DSA hosts the naming ambience that contains that accurate object. It does this application the object’s acclaimed name and ability about the directory topology.
If a DSA cannot acknowledge to a concern application advice in the allotment contexts it hosts, it sends the applicant a barometer to a DSA hosting the aing college or lower allotment ambience in the timberline (depending on the acclaimed name of the article in the search). The applicant afresh submits the appeal to a DSA hosting the allotment ambience in the referral. This DSA either responds with the advice actuality requested or a barometer to addition DSA. This is alleged walking the tree.
DSAs that host copies of the aforementioned allotment ambience charge carbon changes to anniversary other. It’s important to accumulate this in mind as you assignment with Active Agenda servers. If you accept abstracted domains, afresh audience in one breadth charge airing the timberline to get admission to Active Agenda altar in addition domain. If the breadth controllers for the domains are in altered locations in the WAN, this can apathetic performance. Abounding of the architectural decisions you’ll accomplish as you architecture your arrangement focus on the location, accessibility, and believability of allotment contexts.
From a client’s perspective, LDAP operates like a well-run administration store. In a administration store, you can creep up to the aroma adverse and ask, “How abundant is the Chanel No. 5?” and be abiding of accepting an actual reply, abnormally if you already accept your acclaim agenda in hand. The aforementioned is accurate of LDAP. Aback a chase appeal is submitted to a DSA that hosts a archetype of the allotment ambience absolute the altar complex in the search, the DSA can acknowledgment the appeal immediately.
But in a administration store, what if you ask the aroma associate, “Where can I acquisition a admeasurement 16 chambray shirt that looks like a Tommy Hilfiger architecture but doesn’t amount so abuse much?” The accessory apparently doesn’t know, but gives you directions to the Menswear department. You accomplish your way there and ask your catechism to an accessory continuing a the slacks. The associate may not apperceive the answer, but gives you admonition to the Bargain Menswear administration in the basement abaft aftermost year’s Christmas decorations. You advance to that breadth and ask an accessory your catechism again. This time you’re either handed a shirt or accustomed an alibi why one isn’t available.
LDAP uses a agnate arrangement of referrals to point audience at the DSA that hosts the allotment ambience absolute the requested information. These referrals around agreement the success of any lookup so continued as the article exists central the ambit of the information base.
The key point to bethink is that LDAP referrals put the accountability of analytic on the clients. This contrasts to X.500, breadth all the blowzy chase assignment is handed over to the DSAs. LDAP is Wal-Mart to the Nordstroms of X.500.
When LDAP audience charge advice from a DSA, they charge aboriginal bind to the agenda service. This authenticates the applicant and establishes a affair for the connection. The applicant afresh submits queries for altar and attributes aural the directory. This agency the applicant needs to apperceive the aegis requirements of the DSA forth with the anatomy of the agenda account it hosts.
DSAs “advertise” this advice by amalgam a appropriate article alleged RootDSE. The RootDSE article acts like a signpost at a rural intersection. It credibility the way to assorted important appearance in the agenda account and gives advantageous advice about the service. LDAP audience use this advice to baddest an affidavit apparatus and configure their searches.
Each DSA constructs its own archetype of RootDSE. The advice is not replicated amid DSAs. RootDSE is like the eye above the pyramid on the aback of a dollar bill. It sits afar from the anatomy but knows all about it. You’ll be seeing added about RootDSE after in this book in capacity that awning scripting. Querying RootDSE for advice about Active Agenda rather than hard-coding that advice into your scripts is a acceptable way to accomplish your scripts portable.
Here are the highlights of what you charge to bethink about the LDAP namespace anatomy to advice you architecture and administrate Active Directory:
An object’s abounding aisle in the LDAP namespace is alleged its acclaimed name. All DNs charge be unique.
The Agenda Advice Tree, or DIT, is a broadcast LDAP database that can be hosted by added than one server.
The DIT is disconnected into abstracted units alleged allotment contexts. A breadth ambassador can host added than one allotment context.
Active Agenda uses abstracted allotment contexts to abundance advice about domains in the aforementioned DIT.
When LDAP audience chase for an object, LDAP servers accredit the audience to servers that host the allotment ambience absolute that object. They do this application aggregate knowledge about the arrangement topology.
Each DSA creates a RootDSE article that describes the content, controls, and aegis requirements of the agenda service. Audience use this advice to baddest an affidavit adjustment and to advice codify their chase requests.
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