Monday, January 29, 2018

AD Active Directory Interview Questions and Answers

What is Active Directory?

Active Directory (AD) is a directory service developed by Microsoft and used to store objects like User, Computer, printer, Network information, It facilitate to manage your network effectively with multiple Domain Controllers in different location with AD database, able to manage/change AD from any Domain Controllers and this will be replicated to all other DC’s, centralized Administration with multiple geographical location and authenticates users and computers in a Windows domain

What is LDAP and how the LDAP been used on Active Directory(AD)?

What is Tree?
Tree is a hierarchical arrangement of windows Domain that share a contiguous name space

What is Domain?
Active Directory Domain Services is Microsoft’s Directory Server. It provides authentication and authorization mechanisms as well as a framework within which other related services can be deployed

What is Active Directory Domain Controller (DC)?
Domain Controller is the server which holds the AD database, All AD changes get replicated to other DC and vise vase

What is Forest?
Forest consists of multiple Domains trees. The Domain trees in a forest do not form a contiguous name space however share a common schema and global catalog (GC)

What is Schema?
Active directory schema is the set of definitions that define the kinds of object and the type of information about those objects that can be stored in Active Directory
Active directory schema is Collection of object class and there attributes
Object Class = User
Attributes = first name, last name, email, and others

Can we restore a schema partition?


Tel me about the FSMO roles?
Schema Master
Domain Naming Master
Infrastructure Master
RID Master
PDC
Schema Master and Domain Naming Master are forest wide role and only available one on each Forest, Other roles are Domain wide and one for each Domain
AD replication is multi master replication and change can be done in any Domain Controller and will get replicated to others Domain Controllers, except above file roles, this will be flexible single master operations (FSMO), these changes only be done on dedicated Domain Controller so it’s single master replication

How to check which server holds which role?
Netdom query FSMO

Which FSMO role is the most important? And why?
Interesting question which role is most important out of 5 FSMO roles or if one role fails that will impact the end-user immediately
Most armature administrators pick the Schema master role, not sure why maybe they though Schema is very critical to run the Active Directory
Correct answer is PDC, now the next question why? Will explain role by role what happens when a FSMO role holder fails to find the answer

Schema Master – Schema Master needed to update the Schema, we don’t update the schema daily right, when will update the Schema? While the time of operating system migration, installing new Exchange version and any other application which requires extending the schema
So if are Schema Master Server is not available, we can’t able to update the schema and no way this will going to affect the Active Directory operation and the end-user
Schema Master needs to be online and ready to make a schema change, we can plan and have more time to bring back the Schema Master Server

Domain Naming Master – Domain Naming Master required to creating a new Domain and creating an application partition, Like Schema Master we don’t cerate Domain and application partition frequently
So if are Domain Naming Master Server is not available, we can’t able to create a new Domain and application partition, it may not affect the user, user event didn’t aware Domain Naming Master Server is down

Infrastructure Master – Infrastructure Master updates the cross domain updates, what really updates between Domains? Whenever user login to Domain the TGT has been created with the list of access user got through group membership (user group membership details) it also contain the user membership details from trusted domain, Infrastructure Master keep this information up-to-date, it update reference information every 2 days by comparing its data with the Global Catalog (that’s why we don’t keep Infrastructure Master and GC in same server)
In a single Domain and single Forest environment there is no impact if the Infrastructure Master server is down
In a Multi Domain and Forest environment, there will be impact and we have enough time to fix the issue before it affect the end-user

RID Master –Every DC is initially issued 500 RID’s from RID Master Server.  RID’s are used to create a new object on Active Directory, all new objects are created with Security ID (SID) and RID is the last part of a SID. The RID uniquely identifies a security principal relative to the local or domain security authority that issued the SID
When it gets down to 250 (50%) it requests a second pool of RID’s from the RID master.  If RID 

Master Server is not available the RID pools unable to be issued to DC’s and DC’s are only able to create a new object depends on the available RID’s, every DC has anywhere between 250 and 750 RIDs available, so no immediate impact

PDC – PDC required for Time sync, user login, password changes and Trust, now you know why the PDC is important FSMO role holder to get back online, PDC role will impact the end-user immediately and we need to recover ASAP
The PDC emulator Primary Domain Controller for backwards compatibility and it’s responsible for time synchronizing within a domain, also the password master. Any password change is replicated to the PDC emulator ASAP. If a logon request fails due to a bad password the logon request is passed to the PDC emulator to check the password before rejecting the login request.

Tel me about Active Directory Database and list the Active Directory Database files?
NTDS.DIT
EDB.Log
EDB.Che
Res1.log and Res2.log
All AD changes didn’t write directly to NTDS.DIT database file, first write to EDB.Log and from log file to database, EDB.Che used to track the database update from log file, to know what changes are copied to database file.
NTDS.DIT: NTDS.DIT is the AD database and store all AD objects, Default location is the %system root%\nrds\nrds.dit, Active Directory database engine is the extensible storage engine which us based on the Jet database
EDB.Log: EDB.Log is the transaction log file when EDB.Log is full, it is renamed to EDB Num.log where num is the increasing number starting from 1, like EDB1.Log
EDB.Che: EDB.Che is the checkpoint file used to trace the data not yet written to database file this indicate the starting point from which data is to be recovered from the log file in case if failure
Res1.log and Res2.log:  Res is reserved transaction log file which provide the transaction log file enough time to shutdown if the disk didn’t have enough space

Active Directory restores types?
Authoritative restore
Non-authoritative restore

Non-authoritative restore of Active Directory
Non-authoritative restore is restore the domain controller to its state at the time of backup, and allows normal replication to overwrite restored domain controller with any changes that have occurred after the backup. After system state restore, domain controller queries its replication partners and get the changes after backup date, to ensure that the domain controller has an accurate and updated copy of the Active Directory database.
Non-authoritative restore is the default method for restoring Active Directory, just a restore of system state is non-authoritative restore and mostly we use this for Active Directory data loss or corruption.

How perform a non-authoritative restore?
Just start the domain controller in Directory Services Restore Mode and perform system state restore from backup

Authoritative restore of Active Directory
An authoritative restore is next step of the non-authoritative restore process. We have do non-authoritative restore before you can perform an authoritative restore. The main difference is that an authoritative restore has the ability to increment the version number of the attributes of all objects or an individual object in an entire directory, this will make it authoritative restore an object in the directory. This can be used to restore a single deleted user/group and event an entire OU.
In a non-authoritative restore, after a domain controller is back online, it will contact its replication partners to determine any changes since the time of the last backup. However the version number of the object attributes that you want to be authoritative will be higher than the existing version numbers of the attribute, the object on the restored domain controller will appear to be more recent and therefore, restored object will be replicated to other domain controllers in the Domain

How perform a authoritative restore?
Unlike a non-authoritative restore, an authoritative restores need to Ntdsutil.exe to increment the version number of the object attributes

What are Active Directory Partitions can be restored?
You can authoritatively restore only objects from configuration and domain partition. Authoritative restores of schema-naming contexts are not supported.

How many domain controllers need to back up? Or which domain controllers to back up?
Minimum requirement is to back up two domain controllers in each domain, one should be an operations master role holder DC, no need to backup RID Master (relative ID) because RID master should not be restored

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