Understanding Active Directory in Windows

Active Directory was first released in beta form in 1997 when Microsoft came to the point of implementing a Lightweight Directory Access Protocol (LDAP)-based directory service to support its NOS environment.

The first version of the Lightweight Directory Access Protocol (LDAP) was released in 1993 as Request for Comments (RFC) 1487, but due to the absence of many features provided by X.500, it never really took off. It wasn’t until LDAPv2 was released in 1995 as RFC 1777 that LDAP started to gain popularity.

In 1997, the last major update to the LDAP specification, LDAPv3, was described in RFC 2251. It provided several new features and made LDAP robust enough and extensible enough to be suitable for most vendors to implement.

Hierarchical paths in Active Directory are known as distinguished names and can be used to uniquely reference an object. Distinguished names are defined in the LDAP standard as a means of referring to any object in the directory.If the domain had been called mydomain.mycorp.com, the distinguished name of the root would have looked like this:

dc=mydomain,dc=mycorp,dc=com

dc stands for domain component and is used to specify domain or applicationpartition objects.

Active Directory supports using CN, L, O, OU, C, and DC. CN or OU is used in the majority of cases.

Creating Custom Active Directory Attributes

In order to create custom attributes in active directory schema, go to active directory schema snap-in, right click on attributes container and select create attribute. 

Tip – In order to open active directory schema snap-in you need to run command regsvr32 schmmgmt.dll from the Domain Controller. After that you can use MMC and add active directory schema as snap-in. 

Then system will give a warning about the schema object creation and click OK to continue. 

It will open up a form and this is where we need to define the details about custom attribute. 

1) Common Name – This is the name of the object. It is only allowed to use letters, numbers and hyphen for the CN. 

2) LDAP Display Name – When object is referring in script, program or command line utility it need to call using the LDAP Display name instead of the Common Name. when you define the CN, it will automatically create the LDAP Display name. 

3) X500 Object ID – Each and every attribute in active directory schema has unique OID value. There is script develop by Microsoft to generate these unique OID valves. it also can directly run using following PowerShell command. 

 

#--- 

$Prefix="1.2.840.113556.1.8000.2554" 

$GUID=[System.Guid]::NewGuid().ToString() 

$Parts=@() 

$Parts+=[UInt64]::Parse($guid.SubString(0,4),"AllowHexSpecifier") 

$Parts+=[UInt64]::Parse($guid.SubString(4,4),"AllowHexSpecifier") 

$Parts+=[UInt64]::Parse($guid.SubString(9,4),"AllowHexSpecifier") 

$Parts+=[UInt64]::Parse($guid.SubString(14,4),"AllowHexSpecifier") 

$Parts+=[UInt64]::Parse($guid.SubString(19,4),"AllowHexSpecifier") 

$Parts+=[UInt64]::Parse($guid.SubString(24,6),"AllowHexSpecifier") 

$Parts+=[UInt64]::Parse($guid.SubString(30,6),"AllowHexSpecifier") 

$OID=[String]::Format("{0}.{1}.{2}.{3}.{4}.{5}.{6}.{7}",$prefix,$Parts[0],$Parts[1],$Parts[2],$Parts[3],$Parts[4],$Parts[5],$Parts[6]) 

$oid 

#---

 

4) Syntax – It define the storage representation for the object. It is only allowed to use syntaxes defined by Microsoft. One attribute can only associate with one syntax. In below I listed few common used syntaxes in attributes.