Computer Networking Interview Question and Answer

1. Define Network?

A network is a set of devices connected by physical media links. A network is recursively is a connection of two or more nodes by a physical link or two or more networks connected by one or more nodes.

2. What is a Link?

At the lowest level, a network can consist of two or more computers directly connected by some physical medium such as coaxial cable or optical fiber. Such a physical medium is called as Link.

3. What is a node?

A network can consist of two or more computers directly connected by some physical medium such as coaxial cable or optical fiber. Such a physical medium is called as Links and the computer it connects is called as Nodes.

4. What is a gateway or Router?

A node that is connected to two or more networks is commonly called as router or Gateway. It generally forwards message from one network to another.

5. What is point-point link?

If the physical links are limited to a pair of nodes it is said to be point-point link.

6. What is Multiple Access?

If the physical links are shared by more than two nodes, it is said to be Multiple Access.

7. What are the advantages of Distributed Processing?

a. Security/Encapsulation
b. Distributed database
c. Faster Problem solving
d. Security through redundancy
e. Collaborative Processing

16. Define Routing?

The process of determining systematically hoe to forward messages toward the destination nodes based on its address is called routing.

17. What is a peer-peer process?

The processes on each machine that communicate at a given layer are called peer-peer process.

18. When a switch is said to be congested?

It is possible that a switch receives packets faster than the shared link can accommodate and stores in its memory, for an extended period of time, then the switch will eventually run out of buffer space, and some packets will have to be dropped and in this state is said to congested state.

20. What is Round Trip Time?

The duration of time it takes to send a message from one end of a network to the other and back, is called RTT.

21. Define the terms Unicasting, Multiccasting and Broadcasting?

If the message is sent from a source to a single destination node, it is called Unicasting.
If the message is sent to some subset of other nodes, it is called Multicasting.
If the message is sent to all the m nodes in the network it is called Broadcasting.

22. What is Multiplexing?

Multiplexing is the set of techniques that allows the simultaneous transmission of multiple signals across a single data link.

23. Name the categories of Multiplexing?

a. Frequency Division Multiplexing (FDM)
b. Time Division Multiplexing (TDM)
   i. Synchronous TDM
   ii. ASynchronous TDM Or Statistical TDM.
c. Wave Division Multiplexing (WDM)

24. What is FDM?

FDM is an analog technique that can be applied when the bandwidth of a link is greater than the combined bandwidths of the signals to be transmitted.

25. What is WDM?

WDM is conceptually the same as FDM, except that the multiplexing and demultiplexing involve light signals transmitted through fiber optics channel.

26. What is TDM?

TDM is a digital process that can be applied when the data rate capacity of the transmission medium is greater than the data rate required by the sending and receiving devices.

27. What is Synchronous TDM?

In STDM, the multiplexer allocates exactly the same time slot to each device at all times, whether or not a device has anything to transmit.

28. List the layers of OSI

a. Physical Layer
b. Data Link Layer
c. Network Layer
d. Transport Layer
e. Session Layer
f. Presentation Layer
g. Application Layer

29. Which layers are network support layers?

a. Physical Layer
b. Data link Layer and 
c. Network Layers

30. Which layers are user support layers?

a. Session Layer
b. Presentation Layer and 
c. Application Layer

31. Which layer links the network support layers and user support layers?

The Transport layer links the network support layers and user support layers.

32. What are the concerns of the Physical Layer?

Physical layer coordinates the functions required to transmit a bit stream over a physical medium.
a. Physical characteristics of interfaces and media
b. Representation of bits
c. Data rate
d. Synchronization of bits
e. Line configuration
f. Physical topology
g. Transmission mode

33. What are the responsibilities of Data Link Layer?

The Data Link Layer transforms the physical layer, a raw transmission facility, to a reliable link and is responsible for node-node delivery.
a. Framing
b. Physical Addressing
c. Flow Control
d. Error Control
e. Access Control

34. What are the responsibilities of Network Layer?

The Network Layer is responsible for the source-to-destination delivery of packet possibly across multiple networks (links).
a. Logical Addressing
b. Routing

35. What are the responsibilities of Transport Layer?

The Transport Layer is responsible for source-to-destination delivery of the entire message.
a. Service-point Addressing
b. Segmentation and reassembly
c. Connection Control
d. Flow Control
e. Error Control

36. What are the responsibilities of Session Layer?

The Session layer is the network dialog Controller. It establishes, maintains and synchronizes the interaction between the communicating systems.
a. Dialog control
b. Synchronization

37. What are the responsibilities of Presentation Layer?

The Presentation layer is concerned with the syntax and semantics of the information exchanged between two systems.
a. Translation
b. Encryption
c. Compression

38. What are the responsibilities of Application Layer?

The Application Layer enables the user, whether human or software, to access the network. It provides user interfaces and support for services such as e-mail, shared database management and other types of distributed information services.
a. Network virtual Terminal
b. File transfer, access and Management (FTAM)
c. Mail services
d. Directory Services

39. What are the two classes of hardware building blocks?

Nodes and Links.

40. What are the different link types used to build a computer network?

a. Cables
b. Leased Lines
c. Last-Mile Links
d. Wireless Links

41. What are the categories of Transmission media?

a. Guided Media
  i. Twisted - Pair cable
    1. Shielded TP
    2. Unshielded TP
  ii. Coaxial Cable
  iii. Fiber-optic cable
b. Unguided Media
  i. Terrestrial microwave
  ii. Satellite Communication

42. What are the types of errors?

a. Single-Bit error
  In a single-bit error, only one bit in the data unit has changed
b. Burst Error
  A Burst error means that two or more bits in the data have changed.

43. What is Error Detection? What are its methods?

Data can be corrupted during transmission. For reliable communication errors must be deducted and Corrected. Error Detection uses the concept of redundancy, which means adding extra bits for detecting errors at the destination. The common Error Detection methods are 
  a. Vertical Redundancy Check (VRC)
  b. Longitudinal Redundancy Check (VRC)
  c. Cyclic Redundancy Check (VRC)
  d. Checksum

44. What is Redundancy?

The concept of including extra information in the transmission solely for the purpose of comparison. This technique is called redundancy.

45. What is VRC?

It is the most common and least expensive mechanism for Error Detection. In VRC, a parity bit is added to every data unit so that the total number of 1s becomes even for even parity. It can detect all single-bit errors. It can detect burst errors only if the total number of errors in each data unit is odd.

46. What is LRC?

In LRC, a block of bits is divided into rows and a redundant row of bits is added to the whole block. It can detect burst errors. If two bits in one data unit are damaged and bits in exactly the same positions in another data unit are also damaged, the LRC checker will not detect an error. In LRC a redundant data unit follows n data units.

47. What is CRC?

CRC, is the most powerful of the redundancy checking techniques, is based on binary division.

48. What is Checksum?

Checksum is used by the higher layer protocols (TCP/IP) for error detection

49. List the steps involved in creating the checksum.

a. Divide the data into sections
b. Add the sections together using 1's complement arithmetic
c. Take the complement of the final sum, this is the checksum.

Windows System Administrator Interview Question and Answer

1. Q: What does Active Directory mean?

A: The active Directory means a service that identifies and handles resources, making them visible for different groups or members that are authorized. It has the role of an object store. The Active directory sees as objects workstations, people, servers devices or documents and they all have their own characteristics and access control list or ACL.

2.Q: What is the meaning of Global Catalog?

A: A Global Catalog is something that each domain has, and it is used for authenticating the user on the network, on windows 2000 network logon’s were protected from failures by assigning a Global Catalog to every site.

3.Q: What is the use for DHCP?

A: DHCP is used for the DHCP servers, personal computers can get their configuration from a DHCP server on an IP configuration. The server knows nothing about the personal computers until they make a request for information. Usually the most common information sent is IP address and DHCP is used to make a large network administration easier.

 4.Q: What does a Super Scope do in DHCP?

A: The Super Scope gives the DHCP server the possibility to have leases to multiple clients on the same physical network. The leases come from multiple scopes. All scopes must be defined using DHCP manager before the Super Scope creation and they are named member scopes. The DHCP problems can be resolved by the Super Scope in different ways like the following:

a) on a physical network like a LAN network where multiple logical IP networks exist Super Scope is very useful here. These types of networks are also named multinets.

b) there is also need for a Super Scope when the address pool for the current scope becomes empty and there is a need for new computers on the physical network.

c) when clients have to move on another scope.

d) when DHCP clients from the other side of the relay agents (BOOTP) or the network has many logical subnets.

e) when standard networks are limited to leasing addresses for the clients.

5.Q: What main file is used for Active Directory backup and how it is made?

A: Active Directory backup is made using NTbackup utility. The backup is made once with the system state and they are restored also together because they depend on each other. The system state has different components like:

a)    The registry

b)    Boot files or startup files (files required by the operating system to start).

c)    The component services

d)    The system volume or the SYSVOL folder this is a folder that contains files that are shared on a domain.

e)    The Active Directory

6.Q: Does a windows administrator have to be critical?

A: Yes and I can explain how. A system administrator is responsible for an entire network which means he/she must take care of multiple things in the same time which is not an easy task. In order to achieve this, an administrator must have high organization skills and a high technical knowledge and he/she must prevent the problems from happening so that he/she won’t have to be forced to fix them.

7.Q: In what way is forward lookup zone different from the reverse lookup zone in NDS?

A: There is one difference between these two: the forward lookup means name to IP and reverse lookup means IP to name.

8.Q: As a system administrator can you make backup and recovery of data?

A: This is a responsibility that any system administrator must have assume as a basic skill. Of course there are many types of backup that can be made but all must be known for a successful career.

9.Q: What is the meaning of DHCP and  what is the port used by it to work?

A: DHCP or Dynamic Host Configuration Protocol has the ability to assign an IP automatically, this is done in fact by the server and has a number range. When the system starts an IP is assigned automatically. The DHCP server has port number 68, while the client has 67.

10.Q: Can you ensure an updated system all the time and perform market research?

A: Staying up-to-date is another strong point of a professional administrator, technology evolves and we must keep up with the flow, otherwise we can’t do our job in a professional way. Market research is the key to an up-to –date work.

11.Q: Is it possible for a computer to be able to browse the internet without having a default gateway?

A: Yes it is as long as we use a public IP address. The gateway is required as a router or firewall when using an intranet address.

12.Q: What are the advantages or disadvantages  of using DHCP?

A: The advantage is that the DHCP server configures all IP’s automatically and the disadvantage is that when you receive a new IP address the machine name remains the same because of its association with the IP. It’s not a real problem but when somebody tries to access the machine by its name it become one.

13.Q: Are you familiar with monitoring?

A: Yes, monitoring is a base activity of a system administrator, he/she manages all the access rights and the server space, security of the user accounts is one of the most important things here. Also an administrator must make sure that the user’s activity doesn’t affect in any way the integrity of the server.

14.Q: How can we create a SRV record in DNS?

A: To do this we must open the DNS then we must select the abc.local domain the right click and we must go to Other New Records and the SRV ( choose location).

15.Q: In how much time are the security changes applied on the domain controllers?

A: Including policies for personal and public lockout, the changes apply immediately. The changes also include passwords and LSA or Local Security Authority.

16.Q: What do you do if a an end user states that a file is gone?

A: Files are deleted constantly by end users but the backup can restore them. Anyhow before using the backup we must check if the user didn’t move the file by mistake in another place.

17.Q: Where is the storage place of the environmental settings and documents from the roaming profile?

A: These documents and settings are deposited locally until the user’s log off, when they are moved into the shared folder from the server so the log on at a fresh system may take a while because of this.

18.Q: What are the classes that we can find in the Active Directory of Windows Server 2003?

A: We can find:

a)    the abstract class which can be made to look like a template and create other templates, no matter if they are abstract, auxiliary or structural.

b)    the structural class is the important type of class that is made from multiple abstract classes or an existing structural class. They are the only ones that can make Active Directory objects.

c)    the auxiliary class is used as a replace for many attributes of a structural class, it is a list of attributes.

d)    The 88 class is used for objects classes that were defined before 1993 and it is not a common class, it doesn’t use abstract, structural or auxiliary classes.

19.Q: When is a good time for creating a forest?

A: Certain companies that have different bases require different trees and separate namespaces. And unique names sometimes give birth to different identities of DNS. Also companies are sometimes acquired and get under other influences but the continuity must be preserved for the names.

20.Q: Can you explain to us about you experience in the past regarding windows administration?

A: I have ten years of experience in this field, I was passionate about computers since childhood and I installed many operating systems at home and inside organizations including these versions of windows: 95, 98, 98 SE, NT, Millenium, 2000, 2003 Server, XP, Seven, Vista. I also managed these systems and performed maintenance, I worked with different applications from the windows environment.

21.Q: How can you handle a situation in which for instance if you have an application that is not running on Windows 2003 because it’s older?

A: In this situation the application has to be started in the compatibility mode with a previously windows operating system. This is made by right clicking the application icon and choosing another Windows from the compatibility menu.

22.Q: What is the meaning of Repadmin.exe from Windows Server 2008?

A: Repadmin.exe means Replication Diagnostics Tool and helps for the diagnostic of domain controllers in the Windows system. This tool is used by administrators to see the replication topology from the perspective of every domain controller. The active Directory forest can also be supervised by Repadmin.exe and replication problems can be tracked.

23.Q: What difference can we find in the usage of CSVDE versus LDIFDE?

A: CSVDE and LDIFDE are both commands and are used for importing and exporting objects but they are different in the way that CSVDE uses the format CSV (Comma Separated Value) which is an Excel file for files and LDIFDE uses LDIF (LDAP Data Interchange Format) file type which can be viewed with a simple text editor. LDIFDE can be also used for editing or deleting objects unlike CSVDE.

24.Q: What big differences exist between these two operating systems: Windows 2000 and Windows XP?

A: Windows 2000 has more capabilities than Windows XP especially regarding features like DHCP, Terminal Services or DNS. It has all the advantages for server usage. Windows 2000 is a little more professional than XP, but they are both coming with different versions for every user taste. While XP has Home version, Professional or Enterprise, Windows 2000 has Professional and Server editions. The Home version of XP comes with minimal features because the target clients are beginners.

25.Q: What are the things that make Unix different from Windows?

A: The code loading runtime of Unix is different from the one that Windows has. We must become aware of how the system exactly works before we make a dynamically loading module. Unix has the shared objects with the .so extension that encapsulate lines of code that the programs will use and the functions names. These function names become the references of those functions  in the memory of the program when the file is combined with the program. In Windows the .dll file (dynamic-link library file) doesn’t have references and the code of the files does not link to the memory of the program but they get through a lookup table which points to data or functions. Unix has just one type of library file, with the .a extension and the code of many object file is contained within with the .o extension. When the link is created for a shared object file the definition of the identifier may not be found, so the object code from the library will be included.

How to Extend LVM partition online?

One Logical Volume named lv1 is created under vg0. The Initial Size of that Logical Volume is
100MB. Now you required the size 500MB. Successfully make the size of that Logical Volume 500M
without losing any data. As well as size should be increased online.


Answer: In RHEL 4 LVM (Logical Volume Manager) is Version 2. The new feature added is online
extend. In previous version you should unmount the device.
1. Verify the size of Logical Volume: lvdisplay /dev/vg0/lv1
2. Verify the Size on mounted directory: df -h or df -h mounted directory name
3. Use : lvextend -L+400M /dev/vg0/lv1
4. ext2online -d /dev/vg0/lv1 to bring extended size online.
5. Again Verify using lvdisplay and df -h command.
Explanation: The Feature of LVM is dynamically resize the partition. If you resize data, it will not be
lost. LVM Concepts Multiple Physical Disks belongs to the physical group. Using multiple disks
belonging to physical group we can create on the Volume group. Under that Volume Group we can
create multiple Logical Volume and only these Logical Volumes we can use. As well as we can
increase and decrease the size of Logical Volume by using lvextend, lvresize etc.