Computer Networking Interview Questions and Answers

1.	What is a network?
	It is a set of devices connected by communication links. A node can be a computer or any other device capable of sending and/or receiving data generated by other nodes on the network.

2.	What is a protocol?
	It is a set of rules that governs data communication.

3.	What is multiplexing?
	Multiplexing is the process of dividing a link, the phycal medium, into logical channels for better efficiency. Here medium is not changed but it has several channels instead of one.

4.	Define bandwidth?
	The range of frequencies that a medium can pass is called bandwidth. It is the difference between the highest and lowest frequencies that the medium can satisfactorily pass.

5.	What do you mean by switching?
	It is a method in which communication devices are connected to one another efficiently. A switch is intermediary hardware or software that links devices together temporarily.
6.	What are the important topologies for networks?
	BUS topology STAR topology RING topology MESS topology

7.	What are the duties of data link layer?
	Data link layer is responsible for carrying packets from one hop (computer or router) to the next. The duties of data link layer include packetizing, adderssing, error control, flow control, medium access control.

8.	What is virtual channel?
	Virtual channel is normally a connection from one source to one destination, although multicast connections are also permitted. The other name for virtual channel is virtual circuit.

9.	What is multicast routing?
	Sending a message to a group is called multicasting, and its routing algorithm is called multicast routing.

10.	What is TELNET ?
	TELNET is a client - server application that allows a user to log on to a remote machine,giving the user access to the remote system. TELNET is an abbreviation of terminal network.
11.	What do you mean by data communication?
	It is the exchange of data between two devices via some form of transmission medium such as wire cable. The communicating system must be part of a communication system made up of a combination of hardware and software.The effectiveness of a data communication system depends on three fundamental characteristics: delivery, accuracy and timeliness.

12.	What is distributed processing?
	It is a strategy in which services provided by the network reside at multiple sites.

13.	What is point to point connection?
	It provides a dedicated link between two devices. The entire capacity of the link is reserved for transmission between the two devices.

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

15.	What is subnet?
	A generic term for section of a large networks usually separated by a bridge or router.
16.	What is multipoint connection?
	In multipoint connection more than two specific devices share a single link. Here the capacity of the channel is shared either separately or temporally.

17.	What is simplex?
	It is the mode of communication between two devices in which flow of data is unidirectional.

18.	What is half-duplex?
	It is the mode of communication between two devices in which flow of data is bidirectional but not at the same time. ie each station can transmit and receive but not at the same time.

19.	What is full duplex?
	It is the mode of communication between two devices in which flow of data is bidirectional and it occurs simultaneously. Here signals going in either direction share the capacity of the link.

20.	What is a topology?
	Topology of a network is defined as the geometric representation of the relationship of all the links and linking devices (node) to one another .
21.	What is Bandwidth?
	Every line has an upper limit and a lower limit on the frequency of signals it can carry. This limited range is called the bandwidth.

22.	What is point-to-point protocol?
	A communications protocol used to connect computers to remote networking services including Internet service providers.

23.	What is switching?
	Switching in data communication is of three types Circuit switching Packet switching Message switching

24.	Compare analog and digital signals?
	Analog signals can have an infinite number of values in a range but digital signal can have only a limited number of values.

25.	What is the difference between ARP and RARP?
	ARP - Address resolution protocol is used to associate the 32 bit IP address with the 48 bit physical address, used by a host or a router to find the physical address of another host on its network by sending a ARP query packet that includes the IP address of the receiver. RARP - Reverse address resolution protocol allows a host to discover its Internet address when it knows only its physical address.
26.	What is ICMP?
	ICMP is Internet Control Message Protocol, a network layer protocol of the TCP/IP suite used by hosts and gateways to send notification of datagram problems back to the sender.

27.	What is logical link control?
	One of two sublayers of the data link layer of OSI reference model, as defined by the IEEE 802 standard. This sublayer is responsible for maintaining the link between computers when they are sending data across the physical network connection.

28.	What is difference between baseband and broadband transmission?
	In a baseband transmission, the entire bandwidth of the cable is consumed by a single signal. In broadband transmission, signals are sent on multiple frequencies, allowing multiple signals to be sent simultaneously.

29.	What is mesh network?
	A network in which there are multiple network links between computers to provide multiple paths for data to travel.

30.	Define bit rate and bit interval?
	Digital signals are aperiodic.so instead of using period and frequency we use bit interval and bit rate respectively.Bit interval is the time required to send one single bit.Bit rate is the number of bit intervals per second.
31.	What is sampling?
	It is the process of obtaining amplitude of a signal at regular intervals.

32.	Define pulse amplitude modulation?
	It is an analog to digital conversion method which takes analog signals, samples it and generates a series of pulse based on the results of the sampling. It is not used in data communication because the series of pulses generated still of any amplitude. To modify it we use pulse code modulation.

33.	What is Nyquist Theorem?
	According to this theorem, the sampling rate must be at least 2 times the highest frequency of the original signal.

34.	What is Asynchronous mode of data transmission?
	It is a serial mode of transmission.In this mode of transmission, each byte is framed with a start bit and a stop bit. There may be a variable length gap between each byte.

35.	What are the different types of multiplexing?
	Multiplexing is of three types. Frequency division multiplexing and wave division multiplexing is for analog signals and time division multiplexing is for digital signals.
36.	What MAU?
	In token Ring, hub is called Multistation Access Unit(MAU).

37.	What do you mean by switching?
	It is a method in which communication devices are connected to one another efficiently.A switch is intermediary hardware or software that links devices together temporarily.

38.	What do you mean by flow control?
	It is the regulation of sender’s data rate so that the receiver buffer doesn’t become overwhelmed.i.e. flow control refers to a set of procedures used to restrict the amount of data that the sender can send before waiting for acknowledgement.

39.	What do you mean by Bluetooth?
	It is a wireless LAN technology designed to connect devices of different functions such as telephones, notebooks, computers, cameras, printers and so on. Bluetooth LAN Is an adhoc network that is the network is formed spontaneously? It is the implementation of protocol defined by the IEEE 802.15 standard.

40.	What is virtual channel?
	Virtual channel is normally a connection from one source to one destination, although multicast connections are also permitted. The other name for virtual channel is virtual circuit.
41.	What is multicast routing?
	Sending a message to a group is called multicasting, and its routing algorithm is called multicast routing.

42.	What is Mail Gateway?
	It is a system that performs a protocol translation between different electronic mail delivery protocols.

43.	What is IP address?
	The internet address (IP address) is 32bits that uniquely and universally defines a host or router on the internet. The portion of the IP address that identifies the network is called netid. The portion of the IP address that identifies the host or router on the network is called hostid.

44.	What do you mean by subnetting?
	Subnetting divides one large network into several smaller ones. It adds an intermediate level of hierarchy in IP addressing.

45.	What is Firewalls?
	It is an electronic downbridge which is used to enhance the security of a network. It’s configuration has two components. Two routers Application gateway
46.	What is Repeaters ?
	A receiver receives a signal before it becomes too weak or corrupted, regenerates the original bit pattern, sand puts the refreshed copy back onto the link. It operates on phycal layer of OSI model.

47.	What is Bridges?
	They divide large network into smaller components.They can relay frames between two originally separated LANs. They provide security through partitioning traffic. They operate on phycal and data link layer of OSI model.

48.	What is Gateway ?
	It is a protocol converter.A gateway can accept a packet formatted for one protocol and convert it to a packet formatted for another protocol. It operates on all the seven layers of OSI model.

49.	What do you mean by peer ?
	Entities comprising the corresponding layers on different machines are called peers.

50.	What do you mean by broadcasting ?
	Broadcast system allow addressing a packet to all destination by using a special code in address field. when packet is transmitted it is received and processed by every machine on the network.
51.	What is source route?
	It is a sequence of IP addresses identifying the route a datagram must follow. A source route may optionally be included in an IP datagram header.

52.	What are major types of networks?
	Server-based network Peer-to-peer network

53.	What are the protocols in application layer ?
	The protocols defined in application layer are TELNET FTP SMTP SMTP

54.	What do you mean by point to point network?
	Point to point network consist of many connections between individual pair of machines.large networks are point to point.Routing algorithm plays an important in point to point network.It uses stored ad forword technique.It is a packet switching network.
55.	Define Retransmission?
	Retransmission is a technique in which the receiver detects the occurrence of an error and asks the sender to resend the message. Resending is repeated until a message arrives that the receiver believes is error-freed.

56.	What are major types of networks?
	Server-based network Peer-to-peer network

57.	What are the protocols in application layer ?
	The protocols defined in application layer are TELNET FTP SMTP SMTP

58.	What do you mean by point to point network?
	Point to point network consist of many connections between individual pair of machines.large networks are point to point.Routing algorithm plays an important in point to point network.It uses stored ad forword technique.It is a packet switching network.
59.	What are the protocols in transport layer ?
	The protocols defined in transport layer are : TCP UDP

60.	Define TCP ?
	It is connection oriented protocol.It consist byte streams oeiginating on one machine to be delivered without error on any other machine in the network.while transmitting it fragments the stream to discrete messages and passes to interner layer.At the destination it reassembles the messages into output stream.

61.	What is URL ?
	It is a standard for specifying any kind of information on the World Wide Web.

62.	Define UDP ?
	It is unreliable connectionless protocol.It is used for one-shot,client-server type,request reply queries and applications in which prompt delivery is required than accuracy.
63.	What is World Wide Web ?
	World Wide Web is a repository of information spread all over the world and linked together.It is a unique combination of flexibility,portability,and user-friendly features .The World Wide Web today is a distributed client-server service,in which a client using a browser can access a service using a server.The service provided is distributed over many locations called web sites.

64.	What is Hypertext Transfer Protocol(HTTP) ?
	It is the main protocol used to access data on the World Wide Web .the protol transfers data in the form of plain text,hypertext,audio,video,and so on. It is so called because its efficiency allows its use in a hypertext environment where there are rapid jumps from one document to another.

65.	What do you mean by Simple Mail Transfer Protocol ?
	The TCP/IP protocol that supports electronic mail on the internet is called Simple Mail Transfer Protocol.SMTP provides for mail exchange between users on the same or different computer and supports Sending a single message to one or more recipient Sending message that include text, voice,video,or graphics.Sending message to users on network outside the internet.
66.	What do you mean by local login and remote login ?
	When a user logs into a local time-sharing system ,it is called local login. When a user wants to access an application program or utility located on a remote machine,he or she performs remote login.

67.	What is Network Virtual Terminal ?
	A universal interface provided by TELNET is called Network Virtual Terminal(NVT) character set. Via this interface TELNET translates characters (data or command) that come from local terminal into NVT form and delivers them to the network.

Unix/Linux Interview Questions

1.	What is a shell?
	A Unix shell is the program which reads user input from the command line and executes actions based upon that input.

2.	Define session?
	A session is a collection of one or more process groups. A process establishes a new session by calling setsid function. This function returns process group id if OK.

3.	What do you mean by signal?
	Signals are software interrupts. Signals provide a way of handling asynchronous events: a user at a terminal typing the interrupt key to stop a program or the next program in the pipeline terminating prematurely.

4.	What is unix?
	UNIX is the most popular operating system on multi-user systems. This operating system originated as a single-user system. It started off on a cast-off DEC PDP-7 at Bell laboratories in 1969. Ken Thompson, with ideas and help from Dennis Ritchie, and others, wrote a small, general-purpose operating system.

5.	Define message queue?
	message queue Message queue is a linked list of messages. It is used to make a communication between the related or unrelated processes.
6.	Define directory and filename?
	A directory is a file that contains directory entries. The directory entry containing a file name along with structure of information describing the attributes of the file. The names in a directory are called filename. The only two characters that cannot appear in a file name are / and null character.

7.	Define program and process?
	A program is a executable file residing in a disk file. An executing instance of a program is called a process. Every UNIX process have a unique numeric identifier called the process ID. The process ID is always a non negative integer.

8.	List down the different file types?
	Regular file Directory file Character special file Block special file FIFO Symbolic link Socket

9.	What are the options available to determine the group ID of the new file?
	The group ID of the new file can be the effective group ID of the process The group ID of the new file can be the group ID of the directory in which the file is being created.

10.	Define sticky bit?
	The bit S_ISVTX is known as sticky bit. If this bit is set for an executable program file, then the first time the program was executed a copy of the programmer’s text was saved in the swap area when the process terminated. The advantage of using this is the program is loaded into memory faster the next time.
11.	What is called a page fault?
	Page fault is referred to the situation when the process addresses a page in the working set of the process but the process fails to locate the page in the working set. And on a page fault the kernel updates the working set by reading the page from the secondary device.

12.	What do you mean by u-area (user area)?
	This contains the private data that is manipulated only by the Kernel. This is local to the Process, i.e. each process is allocated a u-area.

13.	What are the different types of buffering is supported by UNIX?
	Fuly buffered Line buffered Un buffered

14.	What is the purpose of exec functions?
	When a process calls one of the exec functions that process is completely replaced by the new program. The new program stats execution from main function. The processed does not change across an exec because a new process is not created.But this function replaces the current process with new program from disk.

15.	Define process group?
	A process group is a collection of one or more processes. Each process group has a unique process ID. A function getpgrp returns the process group id of the calling process.
16.	What difference between cmp and diff commands?
	cmp - Compares two files byte by byte and displays the first mismatch. diff - tells the changes to be made to make the files identical.

17.	How many prompts are available in a UNIX system?
	Two prompts, PS1 (Primary Prompt), PS2 (Secondary Prompt).

18.	What are shell variables?
	Shell variables are special variables, a name-value pair created and maintained by the shell.

19.	What is Block Started by Symbol?
	A data representation at the machine level, that has initial values when a program starts and tells about how much space the kernel allocates for the un-initialized data. Kernel initializes it to zero at run-time.

20.	What is the command to find out today’s date?
	date
21.	what are the different commands used to create files?
	touch - to create empty files.(e.g) - touch ‹filename› vi ‹filename› cat>filename .

22.	What is chmod, chown and chgrp?
	Chmod : It is used for to change permissions on files. Chown : It is used for to change ownership of a file. Chgrp : It is used for to change group of the file.

23.	What are PIDs?
	They are process IDs given to processes. A PID can vary from 0 to 65535.

24.	What does the top command display?
	Top command displays the current ammount of memory occupied by the currently executing processes and the details. In addition to memory usage top command displays cpu usage and process details.

25.	What is the command to send message to all users who are logged in?
	Wall
26.	What is Kernel?
	Kernel is core part of unix o/s. It is a group of hundreds of system calls.

27.	What are the different security features in Unix?
	Password protection File permissions Encryption.

28.	What does the swapping system do if it identifies the illegal page for swapping?
	If the disk block descriptor does not contain any record of the faulted page, then this causes the attempted memory reference is invalid and the kernel sends a “Segmentation violation” signal to the offending process. This happens when the swapping system identifies any invalid memory reference.

29.	How do you find out the current directory you’re in?
	pwd
30.	What is a pipe?
	A pipe is two or more commands separated by pipe char ‘|’. That tells the shell to arrange for the output of the preceding command to be passed as input to the following command.

31.	How to close the current user account?
	exit

32.	What is the use of grep command?
	grep is a pattern search command. It searches for the pattern, specified in the command line with appropriate option, in a file(s).

33.	which command is used to identify the type of the file?
	file “grep” means Globally search a regular expression and print it.
34.	What are the features and benefits of unix?
	Portability Machine Independent Multi-user operations Hierarchical file system Unix shell Pipes and filters Utilities Background Processing Software Development Tools Maturity

35.	What is the use of break and continue statements?
	The continue statement suspends execution of all statements following it, and switches control to the top of the loop for the next iteration. The break statement, on the other hand, causes control to break out of the loop.

36.

What is single users system?

The personal computer (PC) is a small, general-purpose system that can execute programs to perform a wide variety of tasks. The PC, however, was designed for use by one person at a time; that is, it is Single-User oriented with MS-DOS as the de facto standard operating system for this range of machines. Single user systems became very popular due to the low cost hardware and wide range of software available for these machines.