Question # 1
Explain Active Directory?
Answer:-
"Active Directory is the directory service used in Windows 2000 Server and is the foundation of Windows 2000 distributed networks."
The core of Active Directory is a combination of an LDAP server and MIT Kerberos 5 KDC running on a Windows 2000 server acting as a domain controller that work as a unit to provide authentication ("Who are you?") and authorization ("What are you allowed to do?") information within a group of interlinked systems.
Above and beyond that, the LDAP "face" of this structure behaves as an enterprise-wide distributed database that not only contains Windows-specific information but can be extended to incorporate user-defined data as well.
The AD is held together by DNS, which is used not only to locate specific machines within the AD but also to locate which functions of the AD are running on which domain controllers.
Question # 2
What is Forest?
Answer:-
The term "forest" is used to describe a collection of AD domains that share a single schema for the AD. All DC's in the forest share this schema and it is replicated in a hierarchical fashion among them. The preferred model for Windows 2000 AD is to have an organization use a single forest that spans an entire enterprise.
While not an administrative block by themselves, forests are a major boundary in that only limited communication is available between forests. For example, it is difficult for a user in one forest to access a resource in another forest.
It is very difficult to integrate forests at this time because of potential problems reconciling schema differences between two forests.
Question # 3
What is Domains in Active Directory?
Answer:-
In Windows 2000, a domain defines both an administrative boundary and a security boundary for a collection of objects that are relevant to a specific group of users on a network. A domain is an administrative boundary because administrative privileges do not extend to other domains. It is a security boundary because each domain has a security policy that extends to all security accounts within the domain. Active Directory stores information about objects in one or more domains.
Domains can be organized into parent-child relationships to form a hierarchy. A parent domain is the domain directly superior in the hierarchy to one or more subordinate, or child, domains. A child domain also can be the parent of one or more child domains, as shown below.
Question # 4
What is Organizational Units?
Answer:-
OU's have many of the attributes of an NT 4 domain. However, instead of requiring server resources to create and support, they are a logical construct within the Active Directory so an OU does not have to support and maintain a domain controller.
OU's are created by an administrator of an AD domain and can be freely named (and renamed). The OU can then be populated objects of many types including computers, groups, printers, users and other sub-OU's.
The real power of an OU is that once it is established, the administrator of its "parent" can delegate administrative authority -- in total or in part -- to any user or group that is in the AD.
When this happens, the designated user/group gains complete administrative authority over all objects in their OU and thus has all of the rights and abilities that a Windows NT domain administrator would have as well as some new ones such as the ability to further segment their OU into sub-OU's and delegate authority over those sub-elements as they see fit.
Question # 5
What is the Group Policy?
Answer:-
Group Policy is one of the most exciting -- and potentially complex -- mechanisms that the Active Directory enables. Group policy allows a bundle of system and user settings (called a "Group Policy Object" or GPO) to be created by an administrator of a domain or OU and have it automatically pushed down to designated systems.
Group Policy can control everything from user interface settings such as screen background images to deep control settings in the client such as its TCP/IP configuration and authentication settings. There are currently over 500 controllable settings. Microsoft has provided some templates as well to provide a starting point for creating policy objects.
A significant advantage of group policy over the old NT-style policies is that the changes they make are reversed when the policy no longer applies to a system. In NT 4, once a policy was applied to a system, removing that policy did not by itself roll back the settings that it imposed on the client. With Windows 2000, when a specified policy no longer applies to a system it will revert to its previous state without administrative interference.
Multiple policies from different sources can be applied to the same object. For example, a domain might have one or more domain-wide policies that apply to all systems in the domain. Below that, systems in an OU can also have policy objects applied to it, and the OU can even be further divided into sub-OU's with their own policies.
This can create a very complex web of settings so administrators must be very careful when creating these multiple layers of policy to make sure the end result -- which is the union of all of the applicable policies with the "closest" policy taking priority in most cases -- is correct for that system. In addition, because Group policy is checked and applied during the system boot process for machine settings and again during logon for user settings, it is recommended that GPO's be applied to a computer from no more than five "layers" in the AD to keep reboot and/or login times from becoming unacceptably long.
Question # 6
What is Empty Root Domain?
Answer:-
The "empty root domain" is an AD design element that has become increasingly popular at organizations with decentralized IT authority such as universities.
The empty root domain acts as a placeholder for the root of Active Directory, and does not typically contain any users or resources that are not required to fulfill this roll [sic]. [...] Only those privileges that have tree or forest-wide scope are restricted to the empty root domain administrators. Departmental administrators can work independently of other departments.
This politically neutral root domain provides a central source of authority and policy enforcement, and provides a single schema and global catalog that allows users to find resources anywhere in the university/district/state system. Individual IT departments retain a significant degree of independence and can control their own users and resources without having to worry that actions by administrators in other departments will disrupt their domain.
Question # 7
What is Mixed Mode?
Answer:-
Allows domain controllers running both Windows 2000 and earlier versions of Windows NT to co-exist in the domain. In mixed mode, the domain features from previous versions of Windows NT Server are still enabled, while some Windows 2000 features are disabled. Windows 2000 Server domains are installed in mixed mode by default. In mixed mode the domain may have Windows NT 4.0 backup domain controllers present. Nested groups are not supported in mixed mode.
Question # 8
What is Native Mode?
Answer:-
When all the domain controllers in a given domain are running Windows 2000 Server. This mode allows organizations to take advantage of new Active Directory features such as Universal groups, nested group membership, and inter-domain group membership.
Question # 9
What is LDAP?
Answer:-
LDAP is the directory service protocol that is used to query and update AD. LDAP naming paths are used to access AD objects and include the following:
• Distinguished names
• Relative Distinguished names
Question # 10
Minimum Requirement for Installing AD?
Answer:-
1. Windows Server, Advanced Server, Datacenter Server
2. Minimum Disk space of 200MB for AD and 50MB for log files
3. NTFS partition
4. TCP/IP Installed and Configured to use DNS
5. Administrative privilege for creating a domain in existing network
Question # 11
How will you verify whether the AD installation is proper?
Answer:-
1. Verify SRV Resource Records
After AD is installed, the DC will register SRV records in DNS when it restarts. We can
check this using DNS MMC or nslookup command. Using MMC
If the SRV records are registered, the following folders will be there in the domain folder in Forward Lookup Zone.
• msdes
• sites
• tcp
• adp
Using nslookup
>nslookup
>ls -t SRV Domain
If the SRV records are properly created, they will be listed.
2. Verifying SYSVOL
If SYSVOL folder is not properly created data stores in SYSVOL such are scripts, GPO, etc will not be replicated between DCs.
First verify the following folder structure is created in SYSVOL Domain
Staging Staging areas Sysvol
Then verify necessary shares are created.
>net share
It should show two shares, NETLOGON and SYSVOL
3. Verifying Database and Log files
Make sure that the following files are there at %systemroot%ntds Ntds.dit, Edb.*, Res*.log
Question # 12
Explain Active Directory schema?
Answer:-
The Active Directory schema is the set of definitions that defines the kinds of objects, and the types of information about those objects, that can be stored in Active Directory. The definitions are themselves stored as objects so that Active Directory can manage the schema objects with the same object management operations used for managing the rest of the objects in the directory.
There are two types of definitions in the schema: attributes and classes. Attributes and classes are also referred to as schema objects or metadata.
Attributes are defined separately from classes. Each attribute is defined only once and can be used in multiple classes. For example, the Description attribute is used in many classes, but is defined once in the schema, assuring consistency.
Question # 13
Can you explain LDAP?
Answer:-
The Lightweight Directory Access Protocol, or LDAP , is an application protocol for querying and modifying data using directory services running over TCP/IP
Question # 14
What is Domain Controller?
Answer:-
In an Active directory forest, the domain controller is a server that contains a writable copy of the Active Directory Database participates in Active directory replication and controls access to network resource.
Question # 15
Define Active Directory?
Answer:-
An active directory is a directory structure used on Microsoft Windows based computers and servers to store information and data about networks and domains.
Question # 16
Why we need Netlogon?
Answer:-
Maintains a secure channel between this computer and the domain controller for authenticating users and services. If this service is stopped, the computer may not authenticate users and services, and the domain controller cannot register DNS records."
Question # 17
Define Kerberos?
Answer:-
Kerberos is a network authentication protocol. It is designed to provide strong authentication for client/server applications by using secret-key cryptography.
Question # 18
Explain What are the standard Port numbers?
Answer:-
SMTP - 25,
POP3 - 110,
IMAP4 - 143,
RPC - 135,
LDAP - 389,
SSL - 443,
HTTP - 80,
RDP - 3389,
DNS - 53,
DHCP - 67,68, FTP-21,
GC-3268,
Secure LDAP - 636, Kerberos - 88,
NNTP - 119,
TFTP - 69,
SNMP - 161.
Question # 19
What is DNS Scavenging?
Answer:-
Scavenging will help you clean up old unused records in DNS.
Question # 20
Explain Where is the AD database held? What other folders are related to AD?
Answer:-
%SystemRoot% tdsNTDS.DIT.
Edb*.log is the transaction log file. Each transaction file is 10 megabytes (MB). When Edb.log file is full, active directory renames it to Edbnnnnn.log, where nnnnn is an increasing number starts from 1.
Edb.chk is a checkpoint file which is use by database engine to track the data which is not yet written to the active directory database file. The checkpoint file act as a pointer that maintains the status between memory and database file on disk. It indicates the starting point in the log file from which the information must be recovered if a failure occurs.
Res1.log and Res2.log: These are reserved transaction log files. The amount of disk space that is reserved on a drive or folder for this log is 20 MB. This reserved disk space provides a sufficient space to shut down if all the other disk space is being used.
Question # 21
How to upgrade from Windows 2003 DC to Windows 2008 DC?
Answer:-
Windows 2003 must be running with SP2 Run adprep /forestprep
Run adprep /domainprep
Start the installation from Windows 2008 DVD Domain level must be in Native Mode
Installation must be started from windows 2003 OS
Question # 22
What is new in Windows Server 2008 Active Directory Domain Services?
Answer:-
AD Domain Services auditing, Fine-Grained Password Policies,Read-Only Domain Controllers,Restartable Active Directory Domain Services
Question # 23
Explain What are RODCs? And what are the major benefits of using RODCs?
Answer:-
Read only Domain Controller, organizations can easily deploy a domain controller in locations where physical security cannot be guaranteed.
Question # 24
Tell me What is the SYSVOL folder?
Answer:-
The Sysvol folder on a Windows domain controller is used to replicate file-based data among domain controllers. %systemroot%SYSVOL
Question # 25
Do you know How frequently is the group policy refreshed?
Answer:-
90 minutes give or take.
Question # 26
What is the number of permitted unsuccessful logons on Administrator account?
Answer:-
Unlimited. Remember, though, that it's the Administrator account, not any account that's part of the Administrators group.
Question # 27
What hidden shares exist on Windows Server 2003 installation?
Answer:-
Admin$, Drive$, IPC$, NETLOGON, print$ and SYSVOL.
Question # 28
What is the List Folder Contents permission on the folder in NTFS?
Answer:-
Same as Read & Execute, but not inherited by files within a folder. However, newly created subfolders will inherit this permission.
Question # 29
Where is GPT stored?
Answer:-
%SystemRoot%SYSVOLsysvoldomainnamePoliciesGUID
Question # 30
Explain GPT and GPC?
Answer:-
Group policy template and group policy container.
Question # 31
Tell me Where are group policies stored?
Answer:-
%SystemRoot%System32GroupPolicy
Question # 32
Explain What is the difference between local, global and universal groups?
Answer:-
Domain local groups assign access permissions to global domain groups for local domain resources. Global groups provide access to resources in other trusted domains. Universal groups grant access to resources in all trusted domains.
Question # 33
Define LSDOU?
Answer:-
It's group policy inheritance model, where the policies are applied to Local machines, Sites, Domains and Organizational Units
Question # 34
Define REPADMIN?
Answer:-
is a command line tool used to monitor and troubleshoot replication on a computer running Windows.
• Checks replication consistency between replication partners.
• Monitors replication status.
• Displays replication metadata.
• Forces replication events.
Question # 35
What is NETDOM?
Answer:-
NETDOM is a command-line tool that allows management of Windows domains and trust relationships
Question # 36
What is ADSIEDIT?
Answer:-
ADSI Edit is an LDAP editor for managing objects in Active Directory. This Active Directory tool lets you view objects and attributes that are not exposed in the Active Directory Management Console.
Question # 37
What is REPLMON?
Answer:-
Replmon is the first tool you should use when troubleshooting Active Directory replication issues
Question # 38
How to find FSMO roles?
Answer:-
Netdom query fsmo OR Replmon.exe
Question # 39
How to view all the GCs in the forest?
Answer:-
repadmin.exe /options * and use IS_GC for current domain options. nltest /dsgetdc:corp /GC
Question # 40
Explain Global Catalog?
Answer:-
A global catalog server is a domain controller that, in addition to its full, writable domain directory partition replica, also stores a partial, read-only replica of all other domain directory partitions in the forest
Global group's membership is limited to accounts from the same domain. The membership is replicated in its own domain only. Universal group's memership is limited to accounts from the same forest.The membership is replicated across the forest
Question # 41
How to view replication properties for AD partitions and DCs?
Answer:-
Replmon
Question # 42
What is the the Directory Partitions?
Answer:-
Schema Partition:
Only one schema partition exists per forest. The schema partition is stored on all domain controllers in a forest. It contains definitions of all objects and attributes that can be created in the directory.
Configuration Partition:
There is only one configuration partition per forest. the configuration partition contains information about the forest-wide active directory structure. Domain Partition:
Many domain partitions can exist per forest. Domain partitions are stored on each domain controller in a given domain. A domain partition contains information about users, groups, computers, and organizational units.
Application Partition:
It stores information about applications in Active Directory. It is replicated only to specific domain controllers.
Question # 43
How to Seize FSMO Roles?
Answer:-
ntdsutil - type roles - connections - connect servername - q - type seize role - at the fsmo maintenance prompt - type seize rid master
Question # 44
How to transfer FSMO Roles?
Answer:-
ntdsutil - type roles - connections - connect servername - q - type transfer role - at the fsmo maintenance prompt - type trasfer rid master
Question # 45
What is a Flexible Single Master Operation?
Answer:-
It is a role that only one DC can (or should) hold at any given time within its boundary.
Schema Master - Use MMC "Active Directory Schema Snap-in". The schema master domain controller controls all updates and modifications to the schema. Once the Schema update is complete, it is replicated from the schema master to all other DCs in the directory.
Domain Naming Master - Use "Active Directory Domains and Trusts". It controls the addition or removal of domains in the forest. Primary Domain Controller (PDC) Emulator - Use the "ADUC" . The PDC emulator is necessary to synchronize time in an enterprise.
Relative ID Master (RID Master) - Use "ADUC". All objects have a SID and a domain SID. The RID assigns relative IDs to each domain controller. Infrastructure Master - Use the "ADUC". Updates group membership information when users from other domains are moved or renamed.
The Infrastructure Master (IM) role should be held by a domain controller that is not a Global Catalog server (GC). If the Infrastructure Master runs on a Global Catalog server it will stop updating object information because it does not contain any references to objects that it does not hold.
Question # 46
What is the ISTG - Intersite topology generator?
Answer:-
ISTG is responsible for creating Active Directory Replication Connection objects for appropriate bridgehead servers within its site. Intersite replication can utilize either RPC over IP or SMTP to convey replication data.
Bridgehead server - A domain controller that is used to send replication information to one or more other sites DHCP Superscope:
A rage of IP address that span several subnets. The DHCP server can assign these address to clients that are on several subnets. DHCP Scope:
A range of IP address that the DHCP server can assign to clients that are on one subnet A stub zone
It is a copy of a zone that contains only those resource records necessary to identify the authoritative Domain Name System (DNS) servers for that zone. A stub zone is used to resolve names between separate DNS namespaces. This type of resolution may be necessary when a corporate merger requires that the DNS servers for two separate DNS namespaces resolve names for clients in both namespaces.
A stub zone consists of: SOA, NS, A Records
Question # 47
What is the KCC (Knowledge consistency checker)?
Answer:-
The KCC generates and maintains the replication topology for replication within sites and between sites. KCC runs every 15 minutes.
Question # 48
How you add a user in ad by commandline?
Answer:-
dsadd
Question # 49
How to do the work with human?
Answer:-
Its very easy please logon to lelopdf.com and see this answer
Question # 50
What is Lightweight Directory Access Protocol?
Answer:-
LDAP is the directory service protocol that is used to query and update AD. LDAP naming paths are used to access AD objects and include the following:
* Distinguished names
* Relative Distinguished names
Question # 51
What is the minimum requirement for installing AD?
Answer:-
* Windows Server, Advanced Server, Data center Server
* Minimum Disk space of 200 MB for AD and 50 MB for log files
* NTFS partition
* TCP/IP Installed and Configured to use DNS
* Administrative privilege for creating a domain in existing network
Question # 52
How will you verify whether the AD installation is proper with SRV resource records?
Answer:-
Verify SRV Resource Records:
After AD is installed, the DC will register SRV records in DNS when it restarts. We can check this using DNS MMC or nslookup command.
Question # 53
How to Verifying SYSVOL?
Answer:-
If SYSVOL folder is not properly created data stores in SYSVOL such are scripts, GPO, etc will not be replicated between DCs. First verify the following folder structure is created in SYSVOL.
* Domain
* Staging
* Staging areas
* Sysvol
Then verify necessary shares are created.
Question # 54
How to verifying database and Log files?
Answer:-
Make sure that the following files are there at %systemroot%ntds Ntds.dit, Edb.*, Res*.log
Question # 55
What is NTDS.DIT?
Answer:-
This is the AD database and stores all AD objects. Default location is SystemRoot%ntdsNTDS.DIT.
Active Directory's database engine is the Extensible Storage Engine which is based on the Jet database and can grow up to 16 TB.
Question # 56
What is NTDS.DIT schema table?
Answer:-
The types of objects that can be created in the Active Directory, relationships between them, and the attributes on each type of object. This table is fairly static and much smaller than the data table.
Question # 57
What is NTDS.DIT Link table?
Answer:-
Link Table contains linked attributes, which contain values referring to other objects in the Active Directory. Take the Member Of attribute on a user object. That attribute contains values that reference groups to which the user belongs. This is also far smaller than the data table.
Question # 58
What is NTDS.DIT Data table?
Answer:-
Data Table users, groups, application-specific data, and any other data stored in the Active Directory.
Question # 59
How many types of Active Directory data?
Answer:-
* Active Directory has three types of data:
* Schema information
* Configuration information
* Domain information
Question # 60
What is Domain information in Active Directory?
Answer:-
Object information for a domain. Replicates to all DCs within a domain. The object portion becomes part of GC. The attribute values only replicates within the domain.
Question # 61
Define Res1.log and Res2.log?
Answer:-
This is reserved transaction log files of 20 MB (10 MB each) which provides the transaction log files enough room to shutdown if the other spaces are being used.
Question # 62
What is ADS Database garbage collection process?
Answer:-
Garbage Collection is a process that is designed to free space within the Active Directory database. This process runs independently on every DC with a default lifetime interval of 12 hours.
Question # 63
List the main steps of Garbage collection process?
Answer:-
* Removing "tombstones" from the database. Tombstones are remains of objects that have been previously deleted.
* Deletion of any unnecessary log files.
* The process launches a defragmentation thread to claim additional free space.
Question # 64
What is Online Defragmentation in Active Directory?
Answer:-
Online Defragmentation method that runs as part of the garbage collection process. The only advantage to this method is that the server does not need to be taken offline for it to run. However, this method does not shrink the Active Directory database file (Ntds.dit).
Question # 65
What is Schema information in Active Directory?
Answer:-
Definitional details about objects and attributes that one CAN store in the AD. Replicates to all DCs. Static in nature.
Question # 66
What is Schema Configuration in Active Directory?
Answer:-
Configuration data about forest and trees. Replicates to all DCs. Static as your forest is.
Question # 67
What is Offline Defragmentation in Active Directory?
Answer:-
Offline Defragmentation is done by taking the server offline and use Ntdsutil.exe to defragment the database. This approach requires that the ADS database be started in repair mode. The advantage to this method is that the database is resized, unused space is removed, and the size is reflected by the Ntds.dit file.
Question # 68
How to do Offline Defragmentation of Active Directory?
Answer:-
Active Directory routinely performs online database defragmentation, but this is limited to the disposal of tombstoned objects. The database file cannot be compacted while Active Directory is mounted.
To defrag ntds.dit offline:
* Back up System State in the backup wizard.
* Reboot and select Directory Services Restore Mode.
* At the command prompt:
* Ntdsutil
* Files
* Info
This will display current information about the path and size of the Active Directory database and its log files.
Compact to D:DbBackup
You must specify a directory path and if the path name has spaces, the command will not work unless you use quotation marks: Quit (till you reach the command prompt)
A new compacted database named Ntds.dit can be found in D:DbBackup.
Copy the new ntds.dit file over the old ntds.dit file. You have successfully compacted the Active Directory database.
Question # 69
Define EDB.LOG?
Answer:-
This is the transaction log file (10 MB). When EDB.LOG is full, it is renamed to EDBnnnn.log. Where nnnn is the increasing number starting from 1.
Question # 70
Define EDB.CHK?
Answer:-
This is the checkpoint file used to track the data not yet written to database file. This indicates the starting point from which data is to be recovered from the log file, in case of failure.
Question # 71
Define Domain Forests in Active Directory?
Answer:-
A forest consists of multiple domain trees. The domain trees in a forest do not form a contiguous namespace but share a common schema and GC. The forest root domain is the first domain created in the forest. The root domains of all domain trees in the forest establish transitive trust relationships with the forest root domain. This is necessary for the purposes of establishing trust across all the domain trees in the forest. All of the Windows 2000 domains in all of the domain trees in a forest share the following traits:
* Transitive trust relationships between the domains
* Transitive trust relationships between the domain trees
* A common schema
* Common configuration information
* A common global catalog
Using both domain trees and forests provides you with the flexibility of both contiguous and non-contiguous naming conventions. This can be useful in, for example, companies with independent divisions that must each maintain their own DNS names.
Question # 72
Define domain Trees in Active Directory?
Answer:-
Tree is a hierarchical arrangement of W2K domains that share a contiguous name space. The first domain in a domain tree is called the root domain. Additional
domains in the same domain tree are child domains. A domain immediately above another domain in the same domain tree is referred to as the parent of the child domain. The name of the chills domain is combined with its parent domain to form its DNS name. Every child domain has a two two-way, transitive trust relationship with its parent domain Because these trust relationships are two-way and transitive, a Windows 2000 domain newly created in a domain tree or forest immediately has trust relationships established with every other Windows 2000 domain in the domain tree or forest.
These trust relationships allow a single logon process to authenticate a user on all domains in the domain tree or forest. This does not necessarily mean that the authenticated user has rights and permissions in all domains in the domain tree. Because a domain is a security boundary, rights and permissions must be assigned on a per-domain basis.
Question # 73
Define Active Directory Schema Attributes?
Answer:-
Attributes are defined separately from classes. Each attribute is defined only once and can be used in multiple classes. For example, the Description attribute is used in many classes, but is defined once in the schema, assuring consistency.
Question # 74
Define Active Directory schema?
Answer:-
The Active Directory schema is the set of definitions that defines the kinds of objects, and the types of information about those objects, that can be stored in Active Directory. The definitions are themselves stored as objects so that Active Directory can manage the schema objects with the same object management operations used for managing the rest of the objects in the directory.
There are two types of definitions in the schema: attributes and classes. Attributes and classes are also referred to as schema objects or metadata.
Question # 75
Define Active Directory Sites?
Answer:-
Site consists of one or more IP subnets connected by a high speed link. Wide area networks should employ multiple sites for efficiently handling servicing requests and reducing replication traffic. Sites map the physical structure of your network whereas domains generally map the logical structure of your organization.
Active Directory Sites and Services allow you to specify site information. Active Directory uses this information to determine how best to use available network resources.
Question # 76
What are the advantages of Active Directory Sites?
Answer:-
Active Directory Sites and Services allow you to specify site information. Active Directory uses this information to determine how best to use available network resources.
Question # 77
Define Active Directory Classes?
Answer:-
Classes, also referred to as object classes; describe the possible directory objects that can be created. Each class is a collection of attributes. When you create an object, the attributes store the information that describes the object. The User class, for example, is composed of many attributes, including Network Address, Home Directory, and so on. Every object in Active Directory is an instance of an object class.
Question # 78
Define Service requests in Active Directory?
Answer:-
When a client requests a service from a domain controller, it directs the request to a domain controller in the same site. Selecting a domain controller that is well-connected to the client makes handling the request more efficient.
Question # 79
What is GC in Active Directory?
Answer:-
GC is created automatically on the first DC in the forest. It stores a full replica of all objects in the directory for its host domain and a partial replica of all objects of every other domain in the forest. The replica is partial because it stores only some attributes for each objects.
