Top 50 IT Interview Questions and Answers

1. Define network?

A network is a collection of computers, servers, mainframes, network devices, peripherals, or other devices connected to one another allowing for data to be shared and used. A great example of a network is the internet, connecting millions of people all over the world together.

2. What is a link?

The link is the physical and logical network component used to interconnect hosts or nodes in the network and a link protocol is a suite of methods and standards that operate only between adjacent network nodes of a local area network segment or a wide area network connection.

3. What is a node?

A node is a basic unit used in computer science. Nodes are devices or data points on a larger network. Devices such as a personal computer, cell phone, or printer arenodes. When defining nodes on the internet, a node is anything that has an ip address.

4. What is a gateway?

A gateway is a network point that acts as an entrance to another network. On the internet, a node or stopping point can be either a gateway node or a host (end-point) node. Both the computers of internet users and the computers that serve pages to users are host nodes.

5. What is point-point link?

In computer networking, point-to-point protocol (ppp) is a data link (layer 2) protocol used to establish a direct connection between two nodes. It can provide connection authentication, transmission encryption (using ecp, rfc 1968), and compression.

6. What is multiple access?

Multiple access is a radio transmission scheme that allows several earth stations to transmit in the same time span. This provides the way to network these stations together, either in a star or a mesh network.

7. What’s the benefit of sub netting?

a- ability to secure your resources by placing them into separate subnetworks

b- ability to organize your resources within a network

c- Speedup your network

8. What is bgp (border gateway protocol)?

Border gateway protocol (bgp) is a standardized exterior gateway protocol designed to exchange routing and reachability information among autonomous systems (as) on the internet. The protocol is often classified as a path vector protocol but is sometimes also classed as a distance-vector routing protocol.

9. What is gateway-to-gateway protocol?

The gateway-to-gateway protocol (ggp) is an obsolete protocol defined for routing datagrams between internet gateways. The gateway-to-gateway protocolwas designed as an internet protocol (ip) datagram service similar to the transmission control protocol (tcp) and the user datagram protocol (udp).

10. What is a multi-homed host?

A multihomed host is physically connected to multiple data links that can be on the same or different networks. For example, a computer with a windows nt 4.0 server and multiple ip addresses can be referred to as "multihomed" and may serve as an ip router.

11. What is ospf?

Open shortest path first (OSPF) is a routing protocol for internet protocol (IP) networks. It uses a link state routing (lsr) algorithm and falls into the group of interior routing protocols, operating within a single autonomous system (as). It is defined as ospf version 2 in rfc 2328 (1998) for ipv4.

12. What is routing?

Routing is the process of selecting best paths in a network. [a] routing is performed for many kinds of networks, including the public switched telephone network (circuit switching), electronic data networks (such as the internet), and transportation networks.

13. What is a protocol?

The tcp/ip internet protocols, a common example, consist of: transmission control protocol (tcp), which uses a set of rules to exchange messages with other internet points at the information packet
level. Internet protocol (ip), which uses a set of rules to send and receive messages at the internet address level.

14. Explain difference between router, switch and hub?

What is a router?

A device that forwards data packets along networks. A router is connected to at least two networks,
commonly two lans or wans or a lan and its isp.s network. Routers are located at gateways, the places
where two or more networks connect. Routers use headers and forwarding tables to determine the best path for forwarding the packets, and they use protocols such as icmp to communicate with each other and configure the best route between any two hosts.

What is a switch?

In networks, a device that filters and forwards packets between LAN segments. Switches operate at the data link layer (layer 2) and sometimes the network layer (layer 3) of the osi reference model and
therefore support any packet protocol. Lans that use switches to join segments are called switched lans or, in the case of Ethernet networks, switched Ethernet LAN.




Finally, what is a hub?

A common connection point for devices in a network. Hubs are commonly used to connect segments of along. A hub contains multiple ports. When a packet arrives at one port, it is copied to the other ports so that all segments of the LAN can see all packets.

14. What is checksum?

A checksum is a count of the number of bits in a transmission unit that is included with the unit so that the receiver can check to see whether the same number of bits arrived. If the counts match, it's assumed that the complete transmission was received. Both tcpand udp communication layers provide a checksum count and verification as one of their services.

15. What is redundancy?

Redundancy is a system design in which a component is duplicated so if it fails there will be a backup. Redundancy has a negative connotation when the duplication is unnecessary or is simply the result of poor planning.

16. What are the criteria necessary for an effective and efficient network?

Criteria necessary for an effective and efficient network. It can be measured in many ways, including transmit time and response time. It is measured by frequency of failure, the time it takes a link to recover from a failure, and the network’s robustness.

17. What is the key advantage of using switches?

A switch is just a another n/w device which has its own advantages and disadvantages as compared to a hub/router/bridge etc ... I hope it doesn't have any disadvantages as such unless and until compared to other n/w devices[note : this is just my opinion,please add details if you have some]

Advantages :

1) reduces the number of broadcast domains

2) supports vlan's which can help in logical segmentation of ports[physical ports].splitting up the broadcast domain.

3) intelligent device[compared to hub's] which can make use of cam table for port to mac mapping

4) compared to bridges ,switches are more h/w oriented therefore operations are less cpu intense[basic operations

5) Thee cost to number of ports ratio is best .. i.e for a cheaper cost you get switches with more number of ports available than routers.

Disadvantages :

1) not as good as a router in limiting broadcasts

2) communication b/w vlan's need intervlan routing [router] ,but these days there are a number of multilayer switches available in the market.

3) handling multicast packets needs quite a bit of configuration & proper designing.

4) at times swtiches when in promiscuos mode is a opening for security attacks [spoofing ip address or capturing ethernet frames using ethereal.

18. When does network congestion occur?

Congestion, in the context of networks, refers to a network state where a node or link carries so much data that it may deteriorate network service quality, resulting in queuing delay, frame or data packet loss and the blocking of new connections. In a congested network, response time slows with reduced network throughput. Congestion occurs when bandwidth is insufficient and network data traffic exceeds capacity.

19. 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.

20. What is the difference between osi and tcp/ip model?

Comparison of osi reference model and tcp/ip reference model

Following are some major differences between osi reference model and tcp/ip reference model, with

diagrammatic comparison below.

Osi(open system interconnection)

1. Osi is a generic, protocol independent standard, acting as a communication gateway between the network and end user.

2. In osi model the transport layer guarantees the delivery of packets.

3. Follows vertical approach.

4. Osi model has a separate presentation layer and session layer.

5. Osi is a reference model around which the networks are built. Generally it is used as a

Tcp/ip(transmission control protocol / internet protocol)

1. Tcp/ip model is based on standard protocols around which the internet has developed. It is a communication protocol, which allows connection of hosts over a network.

2. In tcp/ip model the transport layer does not guarantees delivery of packets. Still the tcp/ip model is more reliable.

3. Follows horizontal approach.

4. Tcp/ip does not have a separate presentation layer or session layer.

5. Tcp/ip model is, in a way implementation of the osi guidance tool.

6. Network layer of osi model provides both connection oriented and connectionless service.

7. Osi model has a problem of fitting the protocols into the model.

8. Protocols are hidden in osi model and are easily replaced as the technology changes.

9. Osi model defines services, interfaces and protocols very clearly and makes clear distinction between them. It is protocol independent.

10. It has 7 layers model.

6. The network layer in tcp/ip model provides connection-less service.

7. Tcp/ip model does not fit any protocol

8. In tcp/ip replacing protocol is not easy.

9. In tcp/ip, services, interfaces and protocols are not clearly separated. It is also protocol dependent.

10. It has 4 layers






21. What is the size of ip address?

The number of unassigned internet addresses is running out, so a new classless scheme called cidr is gradually replacing the system based on classes a, b, and c and is tied to adoption of ipv6. In ipv6 the ip address size is increased from 32 bits to 128 bits.

22. What is the range of class c address? 

C, 192 – 223

23. What is Poe (power over Ethernet)?

Power over Ethernet (Poe) is a technology for wired Ethernet lans (local area networks) that allows the electrical current necessary for the operation of each device to be carried by the data cables rather than by power cords. Doing so minimizes the number of wires that must be strung in order to install the network.

24. What are the advantages of distributed processing?

Distributed data processing is a computer-networking method in which multiple computers across different locations share computer-processing capability. This is in contrast to a single, centralized server managing and providing processing capability to all connected systems. Computers that comprise the distributed data-processing network are located at different locations but interconnected by means of wireless or satellite links.

Advantage: lower cost, reliable, improved performance and reduced processing time, flexible.

25. When were osi model developed and why its standard called 802.xx and so on?

Osi model was developed in february 1980 that why these also known as 802.xx standard (notice 80 means ==> 1980, 2means ==> february)

26. What is full form of AD?

Administrative distance

27. What is a peer-peer process?

In its simplest form, a peer-to-peer (p2p) network is created when two or more pcs are connected and share resources without going through a separate server computer. A p2p network can be an ad hoc connection—a couple of computers connected via a universal serial bus to transfer files.

28. What is the difference between broadcast domain and collision domain?

Collision domain

A collision domain is, as the name implies, a part of a network where packet collisions can occur. A collision occurs when two devices send a packet at the same time on the shared network segment. The packets collide and both devices must send the packets again, which reduces network efficiency.

Collisions are often in a hub environment, because each port on a hub is in the same collision domain.By contrast, each port on a bridge, a switch or a router is in a separate collision domain.

Tip – remember, each port on a hub is in the same collision domain. Each port on a bridge, a switch or router is in a separate collision domain.

Broadcast domain

A broadcast domain is a domain in which a broadcast is forwarded. A broadcast domain contains all
devices that can reach each other at the data link layer (osi layer 2) by using broadcast. All ports on a
hub or a switch are by default in the same broadcast domain. All ports on a router are in the different
broadcast domains and routers don’t forward broadcasts from one broadcast domain to another.

29. What is ping? Why you use ping?

Short for packet internet groper, ping is a utility used to verify whether or not a network data packet is capable of being distributed to an address without errors. The ping utility is commonly used to check for network errors.

Ping is a basic internet program that allows a user to verify that a particular IP address exists and can accept requests.

Ping is used diagnostically to ensure that a host computer the user is trying to reach is actually operating. Ping works by sending an internet control message protocol (icmp) echo request to a specified interface on the network and waiting for a reply. Ping can be used for troubleshooting to test connectivity and determine response time.


30. What is the difference between cross cable and straight cable

Now days, LAN card has intelligence, so that both cables can work.

They have a feature on lots of switches and hubs etc called "auto-mdix" or "auto mdi/mdix", that is the new thing where detect the proper connection type no matter which cable you use.

The cable can be categorized as cat 5, cat 5e, and cat 6 UTP cable. Cat 5 UTP cable can support 10/100 Mbps Ethernet net Ethernet network running at 10/100/1000 Mbps. You might hear about cat 3 utp cable, it's not popular anymore since it Straight and crossover cable can be cat3, cat 5, cat 5e or cat 6 utp cable, the only difference is each type will have different purposes.

Ethernet network cables are straight and crossover cable. This ethernet network cable is made of 4 pair high performance data transmission. Both end of cable is called rj45 connector.

There are two types of network cables commonly used in pc networks - straight-through and cross-over.

Straight cable

Usually use straight cable to connect different type of devices. This type of cable will be used most of the time and can be

1) connect a computer to a switch/hub's normal port.

2) connect a computer to a cable/dsl modem's lan port.

3) connect a router's wan port to a cable/dsl modem's lan port.

4) connect a router's lan port to a switch/hub's uplink port. (normally used for expanding network)

5) connect two switches/hubs with one of the switch/hub using an uplink port and the other one using normal port If you need to check how straight cable looks like, it's easy. Both sides (side a and side b) of cable have wire arrangement

Crossover cable

Sometimes you will use crossover cable, it's usually used to connect same type of devices. A crossover cable can be used

1) connect two computers directly.

2) connect a router's LAN port to a switch/hub's normal port. (normally used for expanding network)

3) connect two switches/hubs by using normal port in both switches/hubs.

If you need to check how crossover cable looks like, both side (side a and side b) of cable have wire arrangement with fol

This cable (either straight cable or cross cable) has total 8 wires (or we can say lines), i.e. Four twisted pairs (4x2=8) with codes. It doesn’t matter what color is given to the cable (but there is a standard).

Purpose of this cross cable is Rx (receiving terminal) connects to Tx (transmitting) of one PC to another PC and vice versa.

As we use two pcs (same devices), straight cable will connect Tx to Tx and Rx to Rx of two computers, so cross cable is require because it has internal arrangement like cross cable. So note that use cross cable to connect two similar devices.

A straight cable will not work to connect two computers together.

Crossover used to connect to pcs directly together, also used for connecting networking devices together like switch to s

Straight cables connect two different types of devices. Whereas crossover cables connect two of the same type

31. What is the difference between tracert and traceroute?

Traceroute:

1) You can find this utility in linux/unix based operating systems.

2) It relies over udp probe packet with destination port: 33434.

3) it uses random source port.

Tracert :

1)you can find this utility in windows based operating systems as well as servers.

2) it rely over icmp type 8(echo packet) & type 0(echo request).

32. What is round trip time?

In telecommunications, the round-trip delay time (rtd) or round-trip time (rtt) is the length of time it takes for a signal to be sent plus the length of time it takes for an acknowledgment of that signal to be received. This time delay therefore consists of the propagation times between the two points of a signal.

33. Define the terms unicasting, multicasting and broadcasting and any casting?

Unicast: a term used in communication to describe a piece of information to send from one point to another. There are only sender and receiver. All lans support unicast transfer mode and most applications that employ tcp transport protocol uses unicast messaging.

Broadcast: a term used for describing communication that is sent a piece of information from one point to all other points. There is one sender and multiple receivers. All lans support broadcast transmission.

Multicast: a term described in communicating a piece of information sent from one or more points to a set of other points. The senders and receivers are one or more.

Anycast is a network addressing and routing methodology in which data-grams from a single sender are routed to the topologically nearest node in a group of potential receivers, though it may be sent to several nodes, all identified by the same destination address.

34. How many pins do serial ports of routers have?

As a 9-pin d connector accessible from the exterior of the case,

35. What are the differences between static IP addressing and dynamic IP addressing?

Difference between static and dynamic ips. When a device is assigned a static ip address, it does not change. The device always has the same ip address. Most devices use dynamic ip addresses, which are assigned by the network when they connect.

36. Difference between csma/cd and csma/ca?

CSMA/CA Vs CSMA/CD

Carrier sense multiple access or csma is a media access control (mac) protocol that is used to control the flow of data in a transmission media so that packets do not get lost and data integrity is maintained. There are two modifications to csma, the csma cd (collision detection) and csma ca (collision avoidance), each having its own strengths.

Csma operates by sensing the state of the medium in order to prevent or recover from a collision. A collision happens when two transmitters transmit at the same time. The data gets scrambled, and the receivers would not be able to discern one from the other thereby causing the information to get lost. The lost information needs to be resent so that the receiver will get it.

Csma cd operates by detecting the occurrence of a collision. Once a collision is detected, csma cd immediately terminates the transmission so that the transmitter does not have to waste a lot of time in continuing. The last information can be re-transmitted. In comparison, csma ca does not deal with the recovery after a collision. What it does is to check whether the medium is in use. If it is busy, then the transmitter waits until it is idle before it starts transmitting. This effectively minimizes the possibility of collisions and makes more efficient use of the medium.

Another difference between csma cd and csma ca is where they are typically used. Csma cd is used mostly in wired installations because it is possible to detect whether a collision has occurred. With wireless installations, it is not possible for the transmitter to detect whether a collision has occurred or not. That is why wireless installations often use csma ca instead of csma cd.

1. Csma/cd takes effect after a collision while Csma/ca takes effect before a collision.

2. Csma/ca reduces the possibility of a collision while csma/cd only minimizes the recovery time.

3. Csma/cd is typically used in wired networks while csma/ca is used in wireless networks.

1. Csma/cd is used in wired lans and csma/ca used in wireless lans and other types of wireless networks.

2. Csma/cd is standardized in ieee 802.3 and csma/ca is standardized in ieee 802.11.

3. Csma/cd will not take steps to prevent transmission collision until it is taken place whilst csma/ca will take actions not to take place any collision since the latter has no means of knowing whether a collision has taken place.

37. What is dhcp scope?

A dynamic host configuration protocol (DHCP) scope is the consecutive range of possible ip addresses that the dhcp server can lease to clients on a subnet. Scopes typically define a single physical subnet on your network to which dhcp services are offered.

38. What are the different memories used in a Cisco router?

Rom, ram, nvram, flash memory

39. What are the different types of passwords used in securing a Cisco router?

The five main passwords of the Cisco Ios are:

Console, aux , vty, enable password, enable secret

40. What is the use of “service password encryption”?

The enable-secret option encrypts your password when you configure the router. When someone looks at your running config, it will not display your "enable" password. However, if you do not use the service password option, when someone views your running config, it will display all passwords except the "enable secret". It will show what your password is for your console line, and vty (telnet). When you do use the service password-encryption, when someone views your running config, those passwords will not be displayed.

41. Briefly explain the conversion steps in data encapsulation.

Transport layer: segment is the pdu of the transport layer.

 Network layer: packet is the pdu of the transport layer.

 Data link layer: frame is the pdu of the transport layer.

 Physical layer: bit is the pdu of the transport layer.

 In configuring a router, what command must be used if you want to delete the configuration data that is stored in the nvram?

Router= erase startup-configuration

42. Ieee standard for wireless networking?

Ieee 802.11 is a set of media access control (mac) and physical layer (phy) specifications for implementing wireless local area network (wlan) computer communication in the 900 mhz and 2.4, 3.6, 5, and 60 ghz frequency bands.

43. What is the range of class a address?

Class a- 0-127

44. What is the range of class b address?

Class b- 128-191

45. Differentiate logical topology from physical topology?

A logical topology is how devices appear connected to the user. A physical topology is how they are actually interconnected with wires and cables. For example, in a shared ethernet network that uses hubs rather than switches, the logical topology appears as if every node is connected to a common bus that runs from node to node. However, its physical topology is a star, in which every node on the network connects to a central hub

46. What is as (autonomous system)?

An autonomous system (as) is a network or a collection of networks that are all managed and supervised by a single entity or organization. An as is a heterogeneous network typically governed by a large enterprise. An as has many different sub-networks with combined routing logic and common routing policies. Each sub-network is assigned a globally unique 16 digit identification number (known as the as number or asn) by the Internet assigned numbers authority (IANA).

47. What is the difference between private ip and public ip?

Public IP address

Connected with the internet network

Publicly registered with network information center

Requires router to connect with a network

Assigned by your ISP.

Private IP address

Connected with a LAN

Is not registered with network information center

Requires modem to connect with a network

Assigned by user or router

48. Explain different cable types?

Coaxial cables

Invented back in the 1880s, "coax" was best known as the kind of cable that connected television sets to home antennas. Coaxial cable is also a standard for 10 mbps ethernet cables. When 10 mbps ethernet was most popular, during the 1980s and early 1990s, networks typically utilized one of two kinds of coaxcable - thinnet (10base2 standard) or thicknet (10base5). These cables consist of an inner copper wire of varying thickness surrounded by insulation and other shielding. Their stiffness caused network administrators difficulty in installing and maintaining thinnet and thicknet.

Twisted pair cables:

Twisted pair eventually emerged during the 1990s as the leading cabling standard for ethernet, starting with 10 mbps (10base-t, also known as category 3 or cat3), later followed by improved versions for 100mbps (100base-tx, cat5 and cat5e) and successively higher speeds up to 10 gbps (10gbase-t).

Fiber optics:

Instead of insulated metal wires transmitting electrical signals, fiber optic network cables work using strands of glass and pulses of light. These network cables are bendable despite being made of glass. They have proven especially useful in wide area network (wans) installations where long distance underground or outdoor cable runs are required and also in office buildings where a high volume of communication traffic is common.

Two primary types of fiber optic cable industry standards are defined – single-mode (100basebx standard) and multi mode (100 bases standard). Long-distance telecommunications networks more commonly use single-mode for its relatively higher bandwidth capacity, while local networks typically use multi mode instead due to its lower cost.

49. How does RIP differ from EIGRP?

Rip stands for routing information protocol and eigrp stands for interior gateway routing protocol.

The major difference between both is that eigrp is Cisco propriety that is it can be implemented only on cisco routers.while this is not the case with rip versions (rip,rip2) they are open standards.

Some internal differences between them are:

1.AD value :that is administrative distance which determines the trust worthiness of the routing protocol. static routing has the highest that is 1. For rip it is 120 for eigrp it is 90 internal / 170 external.

2.Rip uses bellmen ford algorithm to calculate the path while eigrp use dual method to calculate the routes paths

3.Maximum hop count for rip is 15 that is after 15 counts the packet is dropped while that of eigrp is 100 by default and up-to 255 by configuration.

4.There is difference between their refresh timers.

5.There is difference between the ip address which they use to send periodic updates over the network

 6. Eigrp uses an autonomous number to determine which domain it belongs to which is not the case with rip protocols.

7.rip is mostly used for smaller networks which eigrp is used for larger networks. 8.rip is a distance vector routing protocol while eigrp is an link state routing protocol.

9. Rip is classful protocol where as eigrp is classless protocol

10.in rip full routing table exchanged, but in eigrp missing routes are exchanged

11. For rip protocol, hello timers every 30 seconds but in eigrp hello timer every 5 seconds

12. Rip sends full update whenever network change occurs whereas eigrp sends triggered updates

50. Differentiate user mode from privileged mode

User mode (user exec mode)

User mode is the first mode a user has access to after logging into the router. The user mode can be identified by the > prompt following the router name. This mode allows the user to execute only the

basic commands, such as those that show the system's status. The router cannot be configured or restarted from this mode
.
Privileged mode (privileged exec mode)

Privileged mode mode allows users to view the system configuration, restart the system, and enter router configuration mode. Privileged mode also allows all the commands that are available in user mode. Privileged mode can be identified by the # prompt following the router name. From the user mode, a user can change to privileged mode, by running the "enable" command. Also we can keep a enable password or enable secret to restrict access to privileged mode. An enable secret password uses stronger encryption when it is stored in the configuration file and it is safer.

51. What is 100 base-fx?

100 base-fx is a version of fast Ethernet over optical fiber. It uses a 1300 NM near-infrared (nir) light wavelength transmitted via two strands of optical fiber, one for receive (Rx) and the other for transmit (tx).

52. What is Simplex, Half-duplex and Full-duplex?

Simplex: simplex is one direction. A good example would be your keyboard to your cpu. The cpu never needs to send characters to the keyboard but the keyboard always send characters to the cpu. In many cases, computers almost always send characters to printers, but printers usually never send characters to computers (there are exceptions, some printers do talk back). Simplex requires only one lane (in the case of serial).

Half-duplex: half-duplex data transmission means that data can be transmitted in both directions on a signal carrier, but not at the same time. For example, on a local area network using a technology that has half-duplex transmission, one workstation can send data on the line and then immediately receive data on the line from the same direction in which data was just transmitted.

Full-duplex: full-duplex data transmission means that data can be transmitted in both directions on a signal carrier at the same time. For example, on a local area network with a technology that has full-duplex transmission, one workstation can be sending data on the line while another workstation is receiving data. A full-duplex link can only connect two devices, so many such links are required if multiple devices are to be connected together.