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Top 30 CCNA Interview Questions


1)    What is Routing?

Routing is the process of finding a path on which data can pass from source to destination. Routing is done by a device called routers, which are network layer devices.

2)    What is the purpose of the Data Link?

The job of the Data Link layer is to check messages are sent to the right device. Another function of this layer is framing.

3)    What is the key advantage of using switches?

When a switch receives a signal, it creates a frame out of the bits that was extracted from that signal. With this process, it gains access and reads the destination address, after which it forwards that frame to the appropriate port. This is a very efficient means of data transmission, instead of broadcasting it on all ports.

4)    When does network congestion occur?

Network congestion occurs when too many users are trying to use the same bandwidth. This is especially true in big networks that do not resort to network segmentation.

5)    What is a Window in networking terms?

A Window refers to the number of segments that is allowed to be sent from source to destination before an acknowledgement is sent back.

6)    Does a bridge divide a network into smaller segments?

Not really. What a bridge actually does is to take the large network and filter it, without changing the size of the network.

7)    Which LAN switching method is used in CISCO Catalyst 5000?

This model uses the Store-and-forward switching method. It stores the entire frame to its buffers and performs a crc check before deciding whether or not to forward that data frame.

8 ) What is the role of the LLC sublayer?

The LLC sublayer, short for Logical Link Control, can provide optional services to an application developer. One option is to provide flow control to the Network layer by using stop/start codes. The LLC can also provide error correction.

9)    How does RIP differ from IGRP?

RIP relies on the number of hops in order to determine the best route to a network. On the other hand, IGRP takes consideration many factors before it decides the best route to take, such as bandwidth, reliability, MTU and hop count.

10)    What are the different memories used in a CISCO router?

-    NVRAM stores the startup configuration file
-    DRAM stores the configuration file that is being executed
-    Flash Memory - stores the Cisco IOS.

11)    What is BootP?

BootP is a protocol that is used to boot diskless workstations that are connected to the network. It is short for Boot Program. Diskless workstations also use BootP in order to determine its own IP address as well as the IP address of the server PC.

12)    What is the function of the Application Layer in networking?

The Application Layer supports the communication components of an application and provides network services to application processes that span beyond the OSI reference model specifications. It also synchonizes applications on the server and client.

13)    Differentiate User Mode from Privileged Mode

User Mode is used for regular task when using a CISCO router, such as to view system information, connecting to remote devices, and checking the status of the router. On the other hand, privileged mode includes all options that are available for User Mode, plus more. You can use this mode in order to make configurations on the router, including making tests and debugging.

14)    What is 100BaseFX?

This is Ethernet that makes use of fiber optic cable as the main transmission medium. The 100 stands for 100Mbps, which is the data speed.

15)    Differentiate full-duplex from half-duplex.

In full-duplex, both the transmitting device and the receiving device can communicate simultaneously, that is, both can be transmitting and receiving at the same time. In the case of half-duplex, a device cannot receive while it is transmitting, and vice versa.

16)    What is MTU?

MTU stands for Maximum Transmission Unit. It refers to the maximum packet size that can be sent out onto the data line without the need to fragment it.

17)    How does cut-through LAN switching work?

In Cut-Through LAN switching, as soon as the router receives the data frame, it will immediately send it out again and forward it to the next network segment after reading the destination address.

18)    What is latency?

Latency is the amount of time delay that measures the point from which a network device receives a data frame to the time it sends it out again towards another network segment.

19)    Utilizing RIP, what is the limit when it comes to number of hops?

The maximum limit is 15 hop counts. Anything higher than 15 indicates that the network is considered unreachable.

20)    What is a Frame Relay?

Frame Relay is a WAN protocol that provides connection-oriented communication by creating and maintaining virtual circuits. It has a high performance rating and operates at the Data Link and Physical Layers.

21)    How do you configure a Cisco router to route IPX?

The initial thing to do is to enable IPX routing by using the "ipx routing" command. Each interface that is used in the IPX network is then configured with a network number and encapsulation method.

22)    What are the different IPX access lists?

There are two access lists: Standard and Extended. Standard Access List can only filter the source or destination IP address. An Extended Access List uses the source and destination IP addresses, port, socket and protocol when filtering a network.

23)    Explain the benefits of VLANs.

VLANs allow the creation of collision domains by groups other than just physical location. Using VLANs, it is possible to establish networks by different means, such as by function, type of hardware, protocol, among others. This is a big advantage when compared to conventional LANs wherein collision domains are always tied to physical location.

24)    What is subnetting?

Subnetting is the process of creating smaller networks from a big parent network. Being a part of a network, each subnet is assigned some additional parameters or identifier to indicate its subnet number.

25)    What are the advantages of a layered model in the networking industry?

A layered network offers many advantages. It allows administrators to make changes in one layer without the need to make changes in the other layers. Specialization is encouraged, allowing the network industry to make progress faster. A layered model also lets administrators troubleshoot problems more efficiently.

26)    Why is UDP lease favored when compared to TCP?

It's because UDP is unreliable and unsequenced. It is not capable of establishing virtual circuits and acknowledgements.

27)    What are some standards supported by the Presentation layer?

Presentation layer supports many standards, which ensures that data is presented correctly. These include PICT, TIFF and JPEG for graphics, MIDI, MPEG and QuickTime for Video/Audio.

28)    What's the simplest way to remotely configure a router?

In cases when you need to configure a router remotely, the most convenient is to use the Cisco AutoInstall Procedure. However, the router must be connected to the WAN or LAN through one of the interfaces.

29)    What does the show protocol display?

-    routed protocols that is configured on the router
-    the address assigned on each interface
-    the encapsulation method that was configured on each interface

30)    How do you depict an IP address?

It can be done in three possible ways:
-    using Dotted-decimal. For example:
- using Binary. For example: 10000010.00111011.01110010.01110011
-    using Hexadecimal. For example: 82 1E 10 A1

Network Administrator Preparation Questions

Question # 1
Who is network administrator?
Network administrator is responsible for the maintenance of computer hardware and software systems that make up a computer network including the maintenance and monitoring of active data network or converged infrastructure and related network equipment.
Network administrators are generally mid-level support staff within an organization and do not typically get involved directly with users. Network administrators focus on network components within a company's LAN/WAN infrastructure ensuring integrity. Depending on the company and its size, the network administrator may also design and deploy networks.

Question # 2
What is network management?
Network management is the operation, administration, maintenance, and provisioning (OAMP) of networked systems. Network management is essential to command and control practices and is generally carried out of a network operations center.

Question # 3
List the layers of the OSI reference model?
There are 7 OSI reference layers:
*    Physical Layer
*    Data Link Layer
*    Network Layer
*    Transport Layer
*    Session Layer
*    Presentation Layer
*    Application Layer

Question # 4
Explain routers?
Routers can connect two or more network segments. These are intelligent network devices that store information in its routing table such as paths, hops and bottlenecks. With this info, they are able to determine the best path for data transfer. Routers operate at the OSI Network Layer.

Question # 5
Describe point to point link?
Anonymous FTP is a way of granting user access to files in public servers. Users that are allowed access to data in these servers do not need to identify themselves, but instead log in as an anonymous guest.

Question # 6
What is link?

A link refers to the connectivity between two devices. It includes the type of cables and protocols used in order for one device to be able to communicate with the other.

Question # 7
Explain backbone network?
A backbone network is a centralized infrastructure that is designed to distribute different routes and data to various networks. It also handles management of bandwidth and various channels.

Question # 8
Define LAN?
LAN is short for Local Area Network. It refers to the connection between computers and other network devices that are located within a small physical location.

Question # 9
Define node?
A node refers to a point or joint where a connection takes place. It can be computer or device that is part of a network. Two or more nodes are needed in order to form a network connection.

Question # 10
Explain subnet mask?
A subnet mask is combined with an IP address in order to identify two parts: the extended network address and the host address. Like an IP address, a subnet mask is made up of 32 bits.

Question # 11
Explain the maximum length allowed for a UTP cable?
A single segment of UTP cable has an allowable length of 90 to 100 meters. This limitation can be overcome by using repeaters and switches.

Question # 12
What can be considered as good passwords?
Good passwords are made up of not just letters, but by combining letters and numbers. A password that combines uppercase and lowercase letters is favorable than one that uses all upper case or all lower case letters. Passwords must be not words that can easily be guessed by hackers, such as dates, names, favorites, etc. Longer passwords are also better than short ones.

Question # 13
Define the number of network IDs in a class C network?
For a Class C network, the number of usable Network ID bits is 21. The number of possible network IDs is 2 raised to 21 or 2,097,152. The number of host IDs per network ID is 2 raised to 8 minus 2, or 254.

Question # 14
Tell me what happens when you use cables longer than the prescribed length?
Cables that are too long would result in signal loss. This means that data transmission and reception would be affected, because the signal degrades over length.

Question # 15
What common software problems can lead to network defects?
Software related problems can be any or a combination of the following:

*    Client server problems
*    Application conflicts
*    Error in configuration
*    Protocol mismatch
*    Security issues
*    User policy and rights issues

Question # 16
Tell me which protocol can be applied when you want to transfer files between different platforms, such between UNIX systems and Windows servers?
Use FTP (File Transfer Protocol) for file transfers between such different servers. This is possible because FTP is platform independent.

Question # 17
Explain the use of a default gateway?
Default gateways provide means for the local networks to connect to the external network. The default gateway for connecting to the external network is usually the address of the external router port.

Question # 18
Define the proper termination rate for UTP cables?
The proper termination for unshielded twisted pair network cable is 100 ohms.

Question # 19
Explain netstat?
Netstat is a command line utility program. It provides useful information about the current TCP/IP settings of a connection.

Question # 20
What is ping?
Ping is a utility program that allows you to check connectivity between network devices on the network. You can ping a device by using its IP address or device name, such as a computer name.

Question # 21
Define peer to peer?
Peer to peer are networks that does not reply on a server. All PCs on this network act as individual workstations.

Question # 22
Tell me what advantages does fiber optics have over other media?
One major advantage of fiber optics is that is it less susceptible to electrical interference. It also supports higher bandwidth, meaning more data can be transmitted and received. Signal degrading is also very minimal over long distances.

Question # 23
Can you please explain the difference between hub and a switch?
A hub acts as a multi-port repeater. However, as more and more devices connect to it, it would not be able to efficiently manage the volume of traffic that passes through it. A switch provides a better alternative that can improve the performance especially when high traffic volume is expected across all ports.

Question # 24
Explain DNS?

DNS is Domain Name System. The main function of this network service is to provide host names to TCP/IP address resolution.

Question # 25
List the different network protocols that are supported by Windows RRAS services?
There are three main network protocols supported: NetBEUI, TCP/IP, and IPX.

Question # 26
How maximum networks and hosts are in a class A, B and C network?
1)    For Class A, there are 126 possible networks and 16,777,214 hosts
2)    For Class B, there are 16,384 possible networks and 65,534 hosts
3)    For Class C, there are 2,097,152 possible networks and 254 hosts

Question # 27
What is the standard color sequence of a straight-through cable?
Orange/white, orange, green/white, blue, blue/white, green, brown/white, brown.

Question # 28
Tell me what protocols fall under the application layer of the TCP/IP stack?
Following are the protocols under TCP/IP Application layer: FTP, TFTP, Telnet and SMTP.

Question # 29
Is it possible to connect two computers for file sharing without using a hub or router?
Yes, you can connect two computers together using only one cable. A crossover type cable can be use in this scenario. In this setup, the data transmit pin of one cable is connected to the data receive pin of the other cable, and vice versa.

Question # 30
Define ipconfig?
Ipconfig is a utility program that is commonly used to identify the addresses information of a computer on a network. It can show the physical address as well as the IP address.

Question # 31
Can you please explain the difference between straight-through and crossover cable?
A straight-through cable is used to connect computers to a switch, hub or router. A crossover cable is used to connect two similar devices together, such as a PC to PC or Hub to hub.

Question # 32
Explain client/server?
Client/server is a type of network wherein one or more computers act as servers. Servers provide a centralized repository of resources such as printers and files. Clients refers to workstation that access the server.

Question # 33
What is networking?

Networking refers to the inter connection between computers and peripherals for data communication. Networking can be done using wired cabling or through wireless link.

Question # 34
Suppose when you move the NIC cards from one PC to another PC, does the MAC address gets transferred as well?
Yes, that's because MAC addresses are hard-wired into the NIC circuitry, not the PC. This also means that a PC can have a different MAC address when the NIC card was replace by another one.

Question # 35
What is clustering support?
Clustering support refers to the ability of a network operating system to connect multiple servers in a fault-tolerant group. The main purpose of this is the in the event that one server fails, all processing will continue on with the next server in the cluster.

Question # 36
Suppose if a network which contains two servers and twenty workstations, where is the best place to install an Anti-virus program?
An anti-virus program must be installed on all servers and workstations to ensure protection. That's because individual users can access any workstation and introduce a computer virus when plugging in their removable hard drives or flash drives.

Question # 37
What is Ethernet?
Ethernet is one of the popular networking technologies used these days. It was developed during the early 1970s and is based on specifications as stated in the IEEE. Ethernet is used in local area networks.

Question # 38
Give some drawbacks of implementing a ring topology?
In case one workstation on the network suffers a malfunction, it can bring down the entire network. Another drawback is that when there are adjustments and reconfiguration's needed to be performed on a particular part of the network, the entire network has to be temporarily brought down as well.

Question # 39
Can you please explain the difference between CSMA/CD and CSMA/CA?
CSMA/CD, or Collision Detect, retransmits data frames whenever a collision occurred. CSMA/CA, or Collision Avoidance, will first broadcast intent to send prior to data transmission.

Question # 40
What is SMTP?
SMTP is short for Simple Mail Transfer Protocol. This protocol deals with all Internal mail, and provides the necessary mail delivery services on the TCP/IP protocol stack.

Question # 41
Define multicast routing?
Multicast routing is a targeted form of broadcasting that sends message to a selected group of user, instead of sending it to all users on a subnet.

Question # 42
Explain the importance of encryption on a network?

Encryption is the process of translating information into a code that is unreadable by the user. It is then translated back or decrypted back to its normal readable format using a secret key or password. Encryption help ensure that information that is intercepted halfway would remain unreadable because the user has to have the correct password or key for it.

Question # 43
How are IP addresses arranged and displayed?
IP addresses are displayed as a series of four decimal numbers that are separated by period or dots. Another term for this arrangement is the dotted decimal format.  An example is

Question # 44
Explain the importance of authentication?
Authentication is the process of verifying a user's credentials before he can log into the network. It is normally performed using a username and password. This provides a secure means of limiting the access from unwanted intruders on the network.

Question # 45
What is tunnel mode?
This is a mode of data exchange wherein two communicating computers do not use IPSec themselves. Instead, the gateway that is connecting their LANs to the  transit network creates a virtual tunnel that uses the IPSec protocol to secure all communication that passes through it.

Step-by-Step Guide to Getting Started with Hyper-V

Requirements for Hyper-V

Hyper-V has specific hardware and software requirements. The use of this release is limited to specific test environments. The usage limitations are disclosed in the End-User License Agreement, which you must accept to install Hyper-V.

Hardware Requirements and Known Issues

Hyper-V requires an x64-based processor, hardware-assisted virtualization, and hardware data execution protection. Hardware requirements and known issues are included in the release notes. We recommend that you review the release notes before you install Hyper-V.
To download Release Notes for this Release of Hyper-V, see To review the release notes, see

Step 1: Install Hyper-V

You can use Server Manager to install Hyper-V.
 To install Hyper-V
1.    Click Start, and then click Server Manager.
2.    In the Roles Summary area of the Server Manager main window, click Add Roles.
3.    On the Select Server Roles page, click Hyper-V.
4.    On the Create Virtual Networks page, click one or more network adapters if you want to make their network connection available to virtual machines.
5.    On the Confirm Installation Selections page, click Install.
6.    The computer must be restarted to complete the installation. Click Close to finish the wizard, and then click Yes to restart the computer.
7.    After you restart the computer, log on with the same account you used to install the role. After the Resume Configuration Wizard completes the installation, click Close to finish the wizard.

Step 2: Create and set up a virtual machine

After you have installed Hyper-V, you can create a virtual machine and set up an operating system on the virtual machine.
Before you create the virtual machine, you may find it helpful to consider the following questions. You can provide answers to the questions when you use the New Virtual Machine Wizard to create the virtual machine.
•    Is the installation media available for the operating system you want to install on the virtual machine? You can use physical media, a remote image server, or an .ISO file. The method you want to use determines how you should configure the virtual machine.
•    How much memory will you allocate to the virtual machine?
•    Where do you want to store the virtual machine and what do you want to name it?
 To create and set up a virtual machine
1.    Open Hyper-V Manager. Click Start, point to Administrative Tools, and then click Hyper-V Manager.
2.    From the Action pane, click New, and then click Virtual Machine.
3.    From the New Virtual Machine Wizard, click Next.
4.    On the Specify Name and Location page, specify what you want to name the virtual machine and where you want to store it.
5.    On the Memory page, specify enough memory to run the guest operating system you want to use on the virtual machine.
6.    On the Networking page, connect the network adapter to an existing virtual network if you want to establish network connectivity at this point.
If you want to use a remote image server to install an operating system on your test virtual machine, select the external network.
7.    On the Connect Virtual Hard Disk page, specify a name, location, and size to create a virtual hard disk so you can install an operating system on it.
8.    On the Installation Options page, choose the method you want to use to install the operating system:
•    Install an operating system from a boot CD/DVD-ROM. You can use either physical media or an image file (.iso file).
•    Install an operating system from a boot floppy disk.
•    Install an operating system from a network-based installation server. To use this option, you must configure the virtual machine with a network adapter connected to the same network as the image server.
9.    Click Finish.
After you create the virtual machine, you can start the virtual machine and install the operating system.

Step 3: Install the operating system and integration services

In the final step of this process, you connect to the virtual machine to set up the operating system. As part of the setup, you install a software package that improves integration between the virtualization server and the virtual machine.
The instructions in this step assume that you specified the location of the installation media when you created the virtual machine. The instructions also assume that you are installing an operating system for which integration services are available.
 To install the operating system and integration services
1.    From the Virtual Machines section of the results pane, right-click the name of the virtual machine you created in step 2 and click Connect. The Virtual Machine Connection tool will open.
2.    From the Action menu in the Virtual Machine Connection window, click Start.
3.    Proceed through the installation.
•    When you are at the point where you need to provide input to complete the process, move the mouse cursor over the image of the setup window. After the mouse pointer changes to a small dot, click anywhere in the virtual machine window. This action "captures" the mouse so that keyboard and mouse input is sent to the virtual machine. To return the input to the physical computer, press Ctrl-Alt-Left arrow and then move the mouse pointer outside of the virtual machine window.
•    After the operating system is set up, you are ready to install the integration services. From the Action menu of Virtual Machine Connection, click Insert Integration Services Setup Disk. If Autorun does not start the installation automatically, you can start it manually. From a command prompt, type:
After you have completed the setup and integration services are installed, you can proceed to test the virtual machine by customizing it to suit your testing goals. For example, you can view or modify the virtual hardware that is configured for the virtual machine. From the Virtual Machines pane, right-click the name of the virtual machine you created in step 3 and click Settings. From the Settings window, click the name of the hardware to view or change it.
Good Luck

DBA Interview Questions 3

What is Row Migration and Row Chaining?
There are two circumstances when this can occur, the data for a row in a table may be too large to fit into a single data block. This can be caused by either row chaining or row migration.
Chaining: Occurs when the row is too large to fit into one data block when it is first inserted. In this case, Oracle stores the data for the row in a chain of data blocks (one or more) reserved for that segment. Row chaining most often occurs with large rows, such as rows that contain a column of data type LONG, LONG RAW, LOB, etc. Row chaining in these cases is unavoidable.
Migration: Occurs when a row that originally fitted into one data block is updated so that the overall row length increases, and the block’s free space is already completely filled. In this case, Oracle migrates the data for the entire row to a new data block, assuming the entire row can fit in a new block. Oracle preserves the original row piece of a migrated row to point to the new block containing the migrated row: the rowid of a migrated row does not change. When a row is chained or migrated, performance associated with this row decreases because Oracle must scan more than one data block to retrieve the information for that row.
  1. INSERT and UPDATE statements that cause migration and chaining perform poorly, because they perform additional processing.
  2. SELECTs that use an index to select migrated or chained rows must perform additional I/Os.
Detection: Migrated and chained rows in a table or cluster can be identified by using the ANALYZE command with the LIST CHAINED ROWS option. This command collects information about each migrated or chained row and places this information into a specified output table. To create the table that holds the chained rows,
execute script UTLCHAIN.SQL.
SQL> SELECT * FROM chained_rows;
You can also detect migrated and chained rows by checking the ‘table fetch continued row’ statistic in the v$sysstat view.
SQL> SELECT name, value FROM v$sysstat WHERE name = ‘table fetch continued row’;
Although migration and chaining are two different things, internally they are represented by Oracle as one. When detecting migration and chaining of rows you should analyze carefully what you are dealing with.
What is Ora-01555 - Snapshot Too Old error and how do you avoid it?
1. Increase the size of rollback segment. (Which you have already done)
2. Process a range of data rather than the whole table.
3. Add a big rollback segment and allot your transaction to this RBS.
4. There is also possibility of RBS getting shrunk during the life of the query by setting optimal.
5. Avoid frequent commits.
6. Google out for other causes.
What is a locally Managed Tablespace?
A Locally Managed Tablespace is a tablespace that manages its own extents maintaining a bitmap in each data file to keep track of the free or used status of blocks in that data file. Each bit in the bitmap corresponds to a block or a group of blocks. When the extents are allocated or freed for reuse, Oracle changes the bitmap values to show the new status of the blocks. These changes do not generate rollback information because they do not update tables in the data dictionary (except for tablespace quota information), unlike the default method of Dictionary - Managed Tablespaces.
Following are the major advantages of locally managed tablespaces –
• Reduced contention on data dictionary tables 
• No rollback generated 
• No coalescing required 
• Reduced recursive space management.
Can you audit SELECT statements?
      Yes, we can audit the select statements. Check out the below example:
SQL> show parameter audit
———————————— ———– ——————————
audit_file_dest string E:\ORACLE\PRODUCT\10.2.0\DB_2\
audit_sys_operations boolean FALSE
audit_trail string NONE
SQL>  begin
dbms_fga.add_policy ( object_schema => ‘SCOTT’,
object_name => ‘EMP2′,
policy_name => ‘EMP_AUDIT’,
statement_types => ‘SELECT’ );
PL/SQL procedure successfully completed.
SQL>select * from dba_fga_audit_trail;
             no rows selected
In HR schema:
SQL> create table bankim(
name varchar2 (10),
roll number (20));
Table created.
SQL> insert into bankim values (‘bankim’, 10);
1 row created.
SQL> insert into bankim values (‘bankim2′, 20);
1 row created.
SQL> select * from bankim;
———- ———-
bankim 10
bankim2 20
SQL> select name from bankim;
In sys schema:
SQL>set head off
SQL> select sql_text from dba_fga_audit_trail;
select count(*) from emp2
select * from emp2
select * from emp3
select count(*) from bankim
select * from bankim
select name from bankim
What does DBMS_FGA package do?
The dbms_fga Package is the central mechanism for the FGA is implemented in the package dbms_fga, where all the APIs are defined. Typically, a user other than SYS is given the responsibility of maintaining these policies. With the convention followed earlier, we will go with the user SECUSER, who is entrusted with much of the security features. The following statement grants the user SECUSER enough authority to create and maintain the auditing facility.
Grant execute on dbms_fga to secuser;
The biggest problem with this package is that the polices are not like regular objects with owners. While a user with execute permission on this package can create policies, he or she can drop policies created by another user, too. This makes it extremely important to secure this package and limit the use to only a few users who are called to define the policies, such as SECUSER, a special user used in examples.
What is Cost Based Optimization?
The CBO is used to design an execution plan for SQL statement. The CBO takes an SQL statement and tries to weigh different ways (plan) to execute it. It assigns a cost to each plan and chooses the plan with smallest cost.
The cost for smallest is calculated: Physical IO + Logical IO / 1000 + net IO.
How often you should collect statistics for a table?
CBO needs some statistics in order to assess the cost of the different access plans. These statistics includes:
Size of tables, Size of indexes, number of rows in the tables, number of distinct keys in an index, number of levels in a B* index, average number of blocks for a value, average number of leaf blocks in an index
These statistics can be gathered with dbms_stats and the monitoring feature.
How do you collect statistics for a table, schema and Database?
Statistics are gathered using the DBMS_STATS package. The DBMS_STATS package can gather statistics on table and indexes, and well as individual columns and partitions of tables. When you generate statistics for a table, column, or index, if the data dictionary already contains statistics for the object, then Oracle updates the existing statistics. The older statistics are saved and can be restored later if necessary. When statistics are updated for a database object, Oracle invalidates any currently parsed SQL statements that access the object. The next time such a statement executes, the statement is re-parsed and the optimizer automatically chooses a new execution plan based on the new statistics.
Collect Statistics on Table Level
sqlplus scott/tiger
exec dbms_stats.gather_table_stats ( -
     ownname          => 'SCOTT', -
     tabname          => 'EMP', -
     estimate_percent => dbms_stats.auto_sample_size, -
     method_opt       => 'for all columns size auto', -
     cascade          => true, -
     degree           => 5 - )
Collect Statistics on Schema Level
sqlplus scott/tiger
exec dbms_stats.gather_schema_stats ( -
     ownname          => 'SCOTT', -
     options          => 'GATHER', -
     estimate_percent => dbms_stats.auto_sample_size, -
     method_opt       => 'for all columns size auto', -
     cascade          => true, -
     degree           => 5 - )

Collect Statistics on Other Levels
DBMS_STATS can collect optimizer statistics on the following levels, see Oracle Manual
Can you make collection of Statistics for tables automatic?
Yes, you can schedule your statistics but in some situation automatic statistics gathering may not be adequate. It suitable for those databases whose object is modified frequently. Because the automatic statistics gathering runs during an overnight batch window, the statistics on tables which are significantly modified during the day may become stale.
There may be two scenarios in this case:                           
·         Volatile tables that are being deleted or truncated and rebuilt during the course of the day.
·         Objects which are the target of large bulk loads which add 10% or more to the object’s total size.
So you may wish to manually gather statistics of those objects in order to choose the optimizer the best execution plan. There are two ways to gather statistics.
  1. Using DBMS_STATS package.
  2. Using ANALYZE command
How can you use ANALYZE statement to collect statistics?
To delete statistics:
To get the analyze details:
SELECT owner_name, table_name, head_rowid, analyze_timestamp FROM chained_rows;
On which columns you should create Indexes?
The following list gives guidelines in choosing columns to index:
  • You should create indexes on columns that are used frequently in WHERE clauses.
  • You should create indexes on columns that are used frequently to join tables.
  • You should create indexes on columns that are used frequently in ORDER BY clauses.
  • You should create indexes on columns that have few of the same values or unique values in the table.
  • You should not create indexes on small tables (tables that use only a few blocks) because a full table scan may be faster than an indexed query.
  • If possible, choose a primary key that orders the rows in the most appropriate order.
  • If only one column of the concatenated index is used frequently in WHERE clauses, place that column first in the CREATE INDEX statement.
  • If more than one column in a concatenated index is used frequently in WHERE clauses, place the most selective column first in the CREATE INDEX statement.
What type of Indexes is available in Oracle?
  • B-tree indexes: the default and the most common.
  • B-tree cluster indexes: defined specifically for cluster.
  • Hash cluster indexes: defined specifically for a hash cluster.
  • Global and local indexes: relate to partitioned tables and indexes.
  • Reverse key indexes: most useful for Oracle Real Application Clusters.
  • Bitmap indexes: compact; work best for columns with a small set of values
  • Function-based indexes: contain the pre-computed value of a function/expression Domain indexes: specific to an application or cartridge.
What is B-Tree Index?
B-Tree is an indexing technique most commonly used in databases and file systems where pointers to data are placed in a balance tree structure so that all references to any data can be accessed in an equal time frame. It is also a tree data structure which keeps data sorted so that searching, inserting and deleting can be done in logarithmic amortized time.
A table is having few rows, should you create indexes on this table?
You should not create indexes on small tables (tables that use only a few blocks) because a full table scan may be faster than an indexed query.
A Column is having many repeated values which type of index you should create on this column
B-Tree index is suitable if the columns being indexed are high cardinality (number of repeated values). In fact for this situation a bitmap index is very useful but bitmap index are vary expensive.
When should you rebuild indexes?
There is no thumb rule “when you should rebuild the index”. According to expert it depends upon your database situation:
When the data in index is sparse (lots of holes in index, due to deletes or updates) and your query is usually range based or If Blevel >3 then takes index in rebuild consideration; desc DBA_Indexes;
Because when you rebuild indexes then database performance goes down.
In fact binary tree index can never be unbalanced. Binary tree performance is good for both small and large tables and does not degrade with the growth of table.
Can you build indexes online?
Yes, we can build index online. It allows performing DML operation on the base table during index creation. You can use the statements:
ALTER INDEX REBUILD ONLINE is used to rebuild the index online.
A Table Lock is required on the index base table at the start of the CREATE or REBUILD process to guarantee DDL information. A lock at the end of the process also required to merge change into the final index structure.
A table is created with the following setting
                storage (initial 200k
                   next 200k
                   minextents 2
                   maxextents 100
                   pctincrease 40)
What will be size of 4th extent?
Percent Increase allows the segment to grow at an increasing rate.
The first two extents will be of a size determined by the Initial and Next parameter (200k)
The third extent will be 1 + PCTINCREASE/100 times the second extent (1.4*200=280k).
AND the 4th extent will be 1 + PCTINCREASE/100 times the third extent (1.4*280=392k!!!) and so on...
Can you Redefine a table Online?
Yes. We can perform online table redefinition with the Enterprise Manager Reorganize Objects wizard or with the DBMS_REDEFINITION package.
It provides a mechanism to make table structure modification without significantly affecting the table availability of the table. When a table is redefining online it is accessible to both queries and DML during the redefinition process.
Purpose for Table Redefinition
·         Add, remove, or rename columns from a table
·         Converting a non-partitioned table to a partitioned table and vice versa
·         Switching a heap table to an index organized and vice versa
Modifying storage parameters
·         Adding or removing parallel support
·         Reorganize (defragmenting) a table
·         Transform data in a table
Restrictions for Table Redefinition:
·         One cannot redefine Materialized Views (MViews) and tables with MViews or MView Logs defined on them.
·         One cannot redefine Temporary and Clustered Tables
·         One cannot redefine tables with BFILE, LONG or LONG RAW columns
·         One cannot redefine tables belonging to SYS or SYSTEM
·         One cannot redefine Object tables
·         Table redefinition cannot be done in NOLOGGING mode (watch out for heavy archiving)
·         Cannot be used to add or remove rows from a table
Can you assign Priority to users?
Yes, we can do this through resource manager. The Database Resource Manager gives a database administrators more control over resource management decisions, so that resource allocation can be aligned with an enterprise's business objectives.
With Oracle database Resource Manager an administrator can:
  • Guarantee certain users a minimum amount of processing resources regardless of the load on the system and the number of users
  • Distribute available processing resources by allocating percentages of CPU time to different users and applications.
  • Limit the degree of parallelism of any operation performed by members of a group of users
  • Create an active session pool. This pool consists of a specified maximum number of user sessions allowed to be concurrently active within a group of users. Additional sessions beyond the maximum are queued for execution, but you can specify a timeout period, after which queued jobs terminate.
  • Allow automatic switching of users from one group to another group based on administrator-defined criteria. If a member of a particular group of users creates a session that runs for longer than a specified amount of time, that session can be automatically switched to another group of users with different resource requirements.
  • Prevent the execution of operations that are estimated to run for a longer time than a predefined limit
  • Create an undo pool. This pool consists of the amount of undo space that can be consumed in by a group of users.
  • Configure an instance to use a particular method of allocating resources. You can dynamically change the method, for example, from a daytime setup to a nighttime setup, without having to shut down and restart the instance.

Windows Administrator Interview Questions I

Question # 1
What is a desktop?
When you start your computer, the first thing you see is the desktop. The desktop is your work area.

Question # 2
Define Taskbar?
By default, the taskbar is located on the bottom edge of the desktop. You can click the taskbar and drag it to other locations. The Start button, active program buttons, icons for quick access to programs, and the current time are located on the taskbar.

Question # 3
Define My Computer?
The My Computer icon provides access to the resources on your computer. You can access your drives and other peripherals by clicking on the My Computer icon.

Question # 4
Define Recycle Bin?
When you delete an object, Windows XP sends it to the Recycle Bin. You can restore objects that are located in the Recycle Bin or you can permanently delete them.

Question # 5
Define Internet Explorer?
The Internet Explorer icon launches the Internet Explorer browser.

Question # 6
Define Shortcut Icon?
Icons with an arrow in the lower left corner are shortcut icons. Click the icon for quick access to the object they represent (program, document, printer, and so on).

Question # 7
Define Program, folder, and document icons?
Program, folder, and document icons do not have an arrow in the lower left corner. They represent the actual object and provide direct access to the object.

Question # 8

How to start a program?
To start a program:
1)    Click the Start button, located in the lower left corner of your screen.
2)    Highlight Programs. The Program menu will appear.
3)    Move to the Program menu and highlight the program you want to start. If you see a right pointer next to your selection, a sub-menu will appear. Refine your choice by highlighting the appropriate selection on the sub-menu. Continue until you get to the final sub-menu.
4)    Click the program name to start the program.

Question # 9
How to add an item located on my desktop to the Start or to a Program menu?
To add an item on the desktop to the Start or to a Program menu:
1)    Click and drag the item on top of the Start button.
2)    Release the mouse button when the Start menu appears.
3)    The item will appear on the Start menu.
4)    If you would prefer to have the item on a Program menu or sub-menu of the Start menu, drag the item from the Start menu to the Program menu or sub-menu.

Question # 10
What is Windows Explorer?
Windows Explorer is a place where you can view the drives on your computer and manipulate the folders and files. Using Windows Explorer, you can cut, copy, paste, rename, and delete folders and files.

Question # 11
How to open Windows Explorer?
To open Windows Explorer:
1)    Click the Start button, located in the lower left corner of your screen.
2)    Highlight programs.
3)    Highlight Accessories.
4)    Click Windows Explorer.

Question # 12
How to add an item located in Windows Explorer to the Start menu or to a Program menu?
To add an item located in Windows Explorer to the Start menu or to a  Program menu:
*    Click the Start button. The Start menu will appear.
*    Highlight Settings. A submenu will appear.
*    Click Taskbar and Start Menu. A dialog box will appear.
*    Click the Start Menu tab.
*    Click the Customize button.
*    Click Add.
*    Type the path to the item you want to add, or use Browse to navigate to the item.
*    Click Next.
*    Double-click an appropriate folder for the item.
*    Click Finish.
*    Click OK.
*    Click OK again. The item will appear on the menu.

Question # 13
How to remove an item from the Start menu or from a Program menu?
To remove an item from the Start menu or from a Program menu:
*    Click the Start button. The Start menu will appear.
*    Highlight Settings. A submenu will appear.
*    Click Taskbar and Start Menu. A dialog box will appear.
*    Click the Start Menu tab.
*    Click Customize.
*    Click the Remove button.
*    Find and click the item you want to remove.
*    Click the Remove button. You will be prompted.
*    Click Yes.
*    Click Close.
*    Click OK.

*    Click OK again.

Question # 14
How to copy an item that is located on the Start menu or on a Program menu?
To copy an item located on the Start menu or on a Program menu:
1)    Highlight the item.
2)    Right-click. A context menu will appear.
3)    Click Copy.

Question # 15
How to rename an item on the Start menu or on a Program menu?
To rename an item on the Start menu or on a Program menu:
1)    Highlight the item.
2)    Right-click the item.
3)    Click Rename. The Rename dialog box will appear.
4)    Type the new name in the New Name field.
5)    Click OK.

Question # 16
How to delete a file from the Start menu or from a Program menu?
To delete a file from the Start menu or from a Program menu:
1)    Highlight the item.
2)    Right-click.
3)    Click Delete. You will be prompted.
4)    Click Yes.

Question # 17
How to re-sort the Start or a Program menu?
To resort a menu:
1)    Go to the menu.
2)    Right-click.
3)    Click Sort By Name.

Question # 18
How to quickly find files and folders?
Windows XP enables you to quickly locate files and folders on your drives. The search option provides you with four search options: Pictures, music, or video; Documents; All files and folders; and Computers and people. To quickly find a file or folder:
*    Click the Start button. The Start menu will appear.
*    Highlight Search.
*    Click Files or Folders. The Search Results dialog box will open.
*    Choose an option.
*    Enter your search criteria. Use the table that follows to help you.
*    Click search. The results of your search will appear in the right pane.

Question # 19
How to shut down Computer?
To shut down computer:
1)    Click the Start button. The Start menu will appear.
2)    Click Turn Off Computer. The Turn Off Computer dialog box will appear.
3)    Click the Turn Off icon. Your computer will shut down.

Question # 20
How to restart Computer?

You may need to shut down and restart your computer after installing a new program or if your system becomes unstable. To shut down and immediately restart your computer:
1)    Click the Start button. The Start menu will appear.
2)    Click Turn Off Computer. The Turn Off Computer dialog box will appear.
3)    Click the Restart icon. Your computer will restart.

Question # 21
What is Standby mode?
When your computer is in the Standby mode, your computer consumes less electricity, but is ready for immediate use. However, if the computer loses electrical  power while in the standby mode, any information you have not saved will be lost.

Question # 22
How to put Computer in Standby mode?
To put your computer in Standby mode:
1)    Click the Start button. The Start menu will appear.
2)    Click Turn Off Computer. The Turn Off Computer dialog box will appear.
3)    Click the Stand By icon.

Question # 23
Define the field "Look In" in search result?
Select the drive or folder you want to search.

Question # 24
Define the field "A word or phrase in the file" in search result?
If you are looking for a file that has a specific word or phrase in the file, enter the word or phrase in this field.

Question # 25
Define the field "Specify Dates" in search result?
Select from Modified, Created, or Last Accessed. Select Modified to find all files modified since the date criteria you enter, select Created to find all files created since the date criteria you enter, or select Last Accessed to find all files accessed since the date criteria you enter.

Question # 26
Define the field "All or part of the file (document) name" in search result?
Enter the file-name, the first few letters of the file-name, or any letters found in the file-name. Use the * as a wild card. For example, to find all of the files that begin with r and end in the extension .doc, enter r*.doc. To find files that begin with resume and have any extension, enter resume.
If you are looking for a file that has a specific word or phrase in the file-name, enter the word or phrase in this field.

Question # 27
Define the field "Between/During the Previous" in search result?
Specify the date search criteria you want to use. Between allows you to search for files modified, created, or accessed between two dates. During allows you to search for files modified, created, or accessed during the previous number of days or months you specify.

Question # 28
Which is the most recently used document list?
As you work, Windows XP tracks the last 15 files you used. It lists these files on the Most Recently Used Document list. To view the Most Recently Used Document list:
*    Click the Start button.
*    Highlight Documents. The most recently used documents will display.

*    To open a file listed on the Most Recently Used Document list, click the file name.

Question # 29
How to clear my Most Recently Used Document list?
To clear the Most Recently Used Document list:
*    Click the Start button. The Start menu will appear.
*    Highlight Settings.
*    Click Taskbar and Start menu. A dialog box will appear.
*    Click the Start Menu tab.
*    Click Customize.
*    Click Clear.
*    Click OK.
*    Click OK again.

Question # 30
How to change the date and/or time?
To change the date and/or time:
*    Click the Start button, which is located in the lower left corner of the screen. The Start menu will appear.
*    Highlight Settings. A submenu will appear.
*    Click Control Panel. The Control Panel will open.
*    Click Date/Time. The Date/Time Properties dialog box will appear.

Question # 31
How to change the date and/or time in date frame?
*    In the Date frame, select the month and year.
*    In the Month field, click to open the drop-down menu and select the current month.
*    Type the year in the Year field or use the arrows next to the field to move forward or backward until you get to the current year.
*    The Time field is divided into four segments: hour, minutes, seconds, and AM and PM. To make an adjustment:
*    Click in the segment and either type in the correct information or use the arrow keys on the right side to select the correct hour, minute, second or AM or PM.

Question # 32
How to change the time zone?
*    Click the Time Zone tab.
*    Choose the correct time zone from the drop-down menu.
*    If you want the clock to automatically adjust to daylight saving time, check the box on the screen.
*    Click the Apply button.
*    Click OK.

Question # 33
How to install a new printer?
To install a new printer:
*    Make sure your printer is plugged in, connected to your computer, turned on, and has paper in it.
*    Click the Start button. The Start menu will appear.
*    Highlight Settings. A submenu will appear.
*    Click Printers and Faxes. The Printers and Faxes control panel will appear.
*    Double-click on Add Printer. The Add Printer Wizard will open.
*    Follow the onscreen instructions.

Question # 34
How to cancel every print job?
To cancel every print job:
*    Click the Start button. The Start menu will appear.
*    Highlight Settings. A submenu will appear.
*    Click Printers and Faxes. The Printers and Faxes control panel will appear.
*    Double-click the printer to which you sent the print jobs. The Printer window will open.
*    Click Printer, which is located on the menu bar.
*    Click Cancel All Documents.

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