Active Directory Friday: Use the ANR filter for LDAP Queries

ANR or Ambiguous Name Resolution is used to query for objects in Active Directory if the exact identity of an object is not known. A query containing Ambigious Name Resolution will query for all the attributes for example, Given Name, Sur Name, Display Name and samaccountname. For Windows Server 2008 and later versions this is the full list of ANR Attributes included in the search results:

For a full list of all the attributes that are queried please refer to the following TechNet article: ANR Attributes.

  • Display-Name
  • Given-Name
  • Physical-Delivery-Office-Name
  • Proxy-Addresses
  • RDN
  • SAM-Account-Name
  • Surname
  • Legacy-Exchange-DN
  • ms-DS-Additional-Sam-Account-Name
  • ms-DS-Phonetic-Company-Name
  • ms-DS-Phonetic-Department
  • ms-DS-Phonetic-Display-Name
  • ms-DS-Phonetic-First-Name
  • ms-DS-Phonetic-Last-Name

For a full list of all the attributes that are queried please refer to the following TechNet article: ANR Attributes.

An ANR query is useful in a number of scenarios, for example when relying on user input in your script. In this case querying against a samaccountname might fail if the spelling does not match the samaccountname. Similarly an export from a different department or database might be close to what is stored in Active Directory but not an exact match, again this is somewhere where an ANR query might be useful. Something that should be kept in mind is that this is a relatively expensive query and therefore should be avoided when it is not required. In this article we will discuss how to create an ANR filter and what happens exactly in such a query.

In the next example we will be using Get-ADUser cmdlet, which is part of the ActiveDirectory module, in combination with the LDAPFilter parameter in order to execute our query:

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Get-ADUser -LDAPFilter '(anr=Jaap Brasser)'

This will query against all the attributes in the list as ‘Jaap Brasser*’ and two additionally queries: ‘GivenName=Jaap*’ and ‘SurName=Brasser*’ as well as ‘GivenName=Brasser*’ and ‘SurName=Jaap*’. As a result more than one result might be returned, as different attributes of a user account might overlap or are not unique to a single user account. This is the downside of this method of querying.

In the following example I will use the [adsisearcher] type accelerator to execute the same query:

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([adsisearcher]'(anr=Jaap Brasser)').FindAll()

Alternatively the DirectorySearcher object can be manually created to execute a query:

$ADSearcher = New-Object DirectoryServices.DirectorySearcher -Property @{
 Filter = '(anr=Jaap Brasser)'
 PageSize = 100
}
$ADSearcher.FindAll()

For more information on this Ambiguous Name Resolution (ANR) have a look at the following resources:

Ambiguous Name Resolution
MSDN Ambiguous Name Resolution
ANR Attributes
KB Ambiguous Name Resolution for LDAP in Windows 2000
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