Interview Questions Networking

7/31/2019 Interview Questions Networking

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Difference betw een t he comm unication and tra nsm ission.

The differences between the communication and transmission are:

Physical movement of information and concerning about bit priority,synchronization, clock etc is referred as transmission, where as full exchangeof information among media of communication is referred as communication.

Transmission is all about transmitting of data to the destination, where asthe dialogue between the source and destination is all aboutcommunication.

What is the difference between TFTP and FTP application layer

protocols?

The differences between FTP and TFTP:

FTP is connection oriented, where as TFTP is not.TFTP uses error checking and flow control, where as TFTP does not causeerror checking.

FTP uses TCP as transport protocol, where as TFTP uses UDP as transportprotocol.Authentication is mandatory in FTP, where as authentication is not needed inTFTP.

Just getting and putting application effectively is the design concern of TFTP,where as FTP provides more control and data connection aspects.

Difference betw een bi t ra te and baud ra te .

The differences between bit rate and baud rate:

Bit rate is measured as number of data bits transmitted / second in

communication channel.

Baud rate is measured as number of times a signal state is changed in acommunication channel.

One change of state can transmit one bit or less than one bit which dependson modulation technique used. The bit and baud rate have the connection:

bps = baud / second x the number of bits / per baud

W hat are NETBI OS and NETBEUI ?


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Network Basic Input Output System provides session layer of OSI modelrelated services which allows the applications on different computers forcommunicating over a LAN. NetBIOS runs over TCP/IP through NetBIOS overTCP/IP (NBT) protocol. This process results in every computer in the networkwith NetBIOS name and an IP address that corresponds to a host name.

NetBIOS Extended User Interface is an extended version of NetBIOS. It is aprogram that allows computers to communicate within a local area network.NetBEUI forms the frame format which was not a specification of NetBIOS.NetBEUI is the best choice for performing communication within a LAN.

Difference bet w een ARP and RARP.

The differences between ARP and RARP:

Address Resolution Protocol is utilized for mapping IP network address to thehardware address that uses data link protocol.

Reverse Address Resolution Protocol is a protocol using which a physicalmachine in a LAN could request to find its IP address from ARP table orcache from a gateway server.

IP address of destination to physical address conversion is done by ARP, bybroadcasting in LAN.

Physical address of source to IP address conversion is done by RARP.

ARP associates 32 bit IP address with 48 bit physical address.

Allowing a host to discover its internet address after knowing only itsphysical address is done by RARP.

W hat is the difference betw een POP3 a nd I MAP Mail Server?

POP3:All emails are to be downloaded again if used by another desktop PC forchecking the email.May leads to confusion if used for checking email in office and at home pc.Attachments will be down loaded into desktop while the check new email process is in progress.Mailboxes can be created only on desktop and one mail box exists on theserver.


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I MAP:

There is no need for downloading all email while using another desktop PCfor checking email.Unread mail identification is easier.Message downloading is possible only when opened for display from itscontents.Multiple mailboxes creation is possible on the desktop PC and also on theserver.

W hat is a Transaction server?

A transaction server is software that is used for implementing transactions.

A transaction comprises of multiple steps that must automatically becompleted. A transaction server consists of a safety providing system andenvironment where the programs can be written for making use of thefeatures of guaranteed transactions.

W hat i s Message Or iented Middlew are ( MOM) ?

An infrastructure focuses on sending and receiving messages to incrementinteroperability, flexibility and flexibility of an application. MOM performs thisby allowing an application to be distributed over platforms of different kind.MOM reduces the application development complexity which spans multipleoperating systems and network protocols. This process insulates theapplication developer from the operating systems details and networkinterfaces. Various APIs across diverse platforms and networks are providedby MOM.

W hat is Groupw are server?

Groupware server is software that allows the collaboration of users,irrespective of location through the internet or intranet to work together inan atmosphere which is virtual.

W hat are TP-Lite and TP-Heav y Monitors?

TP-Lite Monitor: The integration of TP monitors functions in a databaseengines is called as TP-Lite monitor.

TP-Hea vy Monitor: A TP monitor that supports the client/serverarchitecture and allows PC for initiating very complex multiserver transactionfrom the desktop.


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W hat is LAN?

LAN is a computer network that spans a relatively small area. Most LANs areconfined to a single building or group of buildings. However, one LAN can beconnected to other LANs over any distance via telephone lines and radiowaves. A system of LANs connected in this way is called a wide-areanetwork (WAN). Most LANs connect workstations and personal computers.Each node (individual computer) in a LAN has its own CPU with which itexecutes programs, but it also is able to access data and devices anywhereon the LAN. This means that many users can share expensive devices, suchas laser printers, as well as data. Users can also use the LAN tocommunicate with each other, by sending e-mail or engaging in chatsessions.

W hat ' s the d iff e rence Be tween an I n t r ane t and the I n te rne t?

There's one major distinction between an intranet and the Internet: TheInternet is an open, public space, while an intranet is designed to be aprivate space. An intranet may be accessible from the Internet, but as a ruleit's protected by a password and accessible only to employees or otherauthorized users.

From within a company, an intranet server may respond much more quicklythan a typical Web site. This is because the public Internet is at the mercy of traffic spikes, server breakdowns and other problems that may slow thenetwork. Within a company, however, users have much more bandwidth andnetwork hardware may be more reliable. This makes it easier to serve high-bandwidth content, such as audio and video, over an intranet.

Define the te rm Protocol .

Protocol is a standard way of communicating across a network. A protocol isthe "language" of the network. It is a method by which two dissimilarsystems can communicate. TCP is a protocol which runs over a network.

Def ine File Tra nsfe r Protocol.

File Transfer Protocol (FTP), a standard Internet protocol, is the simplestway to exchange files between computers on the Internet. Like theHypertext Transfer Protocol (HTTP), which transfers displayable Web pagesand related files, and the Simple Mail Transfer Protocol (SMTP), whichtransfers e-mail, FTP is an application protocol that uses the Internet'sTCP/IP protocols. FTP is commonly used to transfer Web page files from theircreator to the computer that acts as their server for everyone on the


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Internet. It's also commonly used to download programs and other files toyour computer from other servers.

What is FTP (File Transfer Protocol)?

FTP is File Transfer Protocol. It used to exchange files on the internet. Toenable the data transfer FTP uses TCP/IP, FTP is most commonly used toupload and download files from the internet. FTP can be invoked from thecommand prompt or some graphical user interface. FTP also allows toupdate (delete, rename, move, and copy) files at a server. It uses areserved port no 21.

Explain the 7 Layers of OSI .

Laye r 1 : Physical laye rIt represents all the electrical and physical specifications for devices.

Layer 2 : Data l ink layerIt provides the functional and procedural means to transfer data betweennetwork entities and to detect and possibly correct errors that may occur inthe Physical layer.

Layer 3 : Net w ork layerThe Network layer provides the functional and procedural means of transferring variable length data sequences from a source to a destinationvia one or more networks.

Layer 4 : Transport layerIt provides transparent transfer of data between end users.

Laye r 5 : Session layerIt controls the sessions between computers. It connects, manages andterminates the connections between the local and remote application.

Layer 6 : Presenta t ion layerIt transforms data to provide a standard interface for the Application layer.

Laye r 7 : Applicat ion layerIt provides a means for the user to access information on the networkthrough an application.

W hat is a netw ork? W hat are t he different k inds of netw ork? Explainthem


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A network is a group of computers or nodes connected together. They areconnected with each other by communication paths.

Types of Netw orks:

LAN Local Area Network connects a group of nodes covering a smallphysical area. LANs are most commonly seen in offices, building etc. LANsenable higher transfer rate of data, smaller coverage of area and hence lesswiring.

W AN Wide Area Network connects a group of nodes covering a wide area.WAN typically connects and allow communication between regions ornational boundaries. The most common example of WAN is internet.

VPN Virtual Private Network connects or links nodes in some larger areaby open connections or virtual circuits in some larger network (e.g., theInternet) instead of by physical wires. It is used for secure communicationthrough the public internet. VPN alone may not support explicit securityfeatures, such as authentication or content encryption.

I n t ra n et It is a set of networks under the control of a singleadministrative person. It can be considered as an internal network of anorganization. If it is large, web servers are used to provide information tothe users.

Extranet It is a network that restricts itself within a single organization. Itcan be categorized as WAN, MAN etc. however; it cannot have a single LAN.It must have a connection (at least one) with external network.

W hat a re net w ork topologies? Explain Ring, Bus and Sta r topology.

A network topology describes the layout of a network. It describes howdifferent nodes and elements are connected to each other. Different types of topology:

a. Ring:-

All nodes connected with another in a loop. Each device is connected to one or more another device on either side.

b. Bus

All nodes connected to a central and a common cable called as a backbone.


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In bus topology, the server is at one end and the clients are connectedat different positions across the network.

Easy to manage and install. If the backbone fails, the entire communication fails.

c. Star

All nodes connected to a central hub. The communication between the nodes is through the hub. Relative requires more cables as compared to BUS. However if any

node fails, it wont affect the entire LAN.

Explain I P, TCP and UD P.

TCP Transmission control Protocol is used to establish communicationbetween nodes or networks and exchange data packets. It guaranteesdelivery of data packets in the order they were sent. Hence it is mostcommonly used in all applications that require guaranteed delivery of data.It can handle both timeouts (if packets were delayed) and retransmission (if packets were lost). The stream of data is transmitted in segments. Thesegment header is 32 bit. it is a connectionless communication protocol atthe third level (network) of the OSI model.

I P Internet protocol is used for transmission of data over the internet. IPuses IP addresses to identity each machine uniquely. Message is sent usingsmall packets. The packet contains both the sender and receivers address.IP does not guarantee the delivery in the same order as sent. This isbecause the packets are sent via different routes. It is a connectionlesscommunication protocol at the third level (network) of the OSI model.

UD P User Data Protocol is a communication protocol. It is normally usedas an alternative for TCP/IP. However there are a number of differencesbetween them. UDP does not divide data into packets. Also, UDP does notsend data packets in sequence. Hence, the application program must ensure

the sequencing. UDP uses port numbers to distinguish user requests. It alsohas a checksum capability to verify the data.

W hat is m ult icast ing?

Multicasting allows a single message to be sent to a group of recipients.Emailing, teleconferencing, are examples of multicasting. It uses thenetwork infrastructure and standards to send messages.

Explain the functionality of PI NG.


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Ping Is particularly used to check if the system is in network or not. It alsogives packet lost information. In windows ping command is written as pingip address. The output returns the data packets information. The number of packets sent, received and lost is returned by PING.

Explain the core naming me chanism, Domain Na me System ( DNS) .

A Domain Name system is used to convert the names of the website on theinternet to IP addresses. The domain names for each IP addresses arestored in a database that is distributed across different servers. A domainname space consists of a tree of domain names. The tree has zones. Zonesconsist of a collection of connected nodes. These nodes are served by aname server. A domain name is usually in the form of mydomain.com. Here,

.com is the top level domain. Whereas my domain is the sub domain orsubdivision. A host name is a domain name that has one or more IPaddresses associated with it.

What is Application layer?

The application layer is located at the top of the TCP/IP protocol layers. Thisone contains the network applications which make it possible tocommunicate using the lower layers. The software in this layer thereforecommunicates using one of the two protocols of the layer below (thetransport layer), i.e. TCP or UDP. In computer networking, an applicationlayer firewall is a firewall operating at the application layer of a protocolstack.[1] Generally it is a host using various forms of proxy servers to proxytraffic instead of routing it. As it works on the application layer, it mayinspect the contents of the traffic, blocking what the firewall administratorviews as inappropriate content, such as certain websites, viruses, andattempts to exploit known logical flaws in client software, and so forth. Anapplication layer firewall does not route traffic on the network layer. Alltraffic stops at the firewall which may initiate its own connections if thetraffic satisfies the rules.

Def ine D NS

The DNS translates Internet domain and host names to IP addresses. DNSautomatically converts the names we type in our Web browser address barto the IP addresses of Web servers hosting those sites. DNS implements adistributed database to store this name and address information for allpublic hosts on the Internet.

Define Telnet


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Telnet is the main Internet protocol for creating a connection to a remoteserver.

Define SMTP.

SMTP - Short for Simple Mail Transfer Protocol, a protocol for sending e-mailmessages between servers.

W hat I s a MAC Address?

MAC (Media Access Control) addresses are globally unique addressed thatare written into hardware at the time of manufacture. The MAC address is aunique value associated with a network adapter. MAC addresses are also

known as hardware addresses or physical addresses. They uniquely identifyan adapter on a LAN. MAC addresses are 12-digit hexadecimal numbers (48bits in length).

MAC vs. I P Addressing

Whereas MAC addressing works at the data link layer, IP addressingfunctions at the network layer (layer 3). It's a slight oversimplification, butone can think of IP addressing as supporting the software implementationand MAC addresses as supporting the hardware implementation of thenetwork stack. The MAC address generally remains fixed and follows thenetwork device, but the IP address changes as the network device movesfrom one network to another.

Define Spanning-Tree Protocol ( STP)

Spanning-Tree Protocol (STP) as defined in the IEEE 802.1D is a linkmanagement protocol that provides path redundancy while preventingundesirable loops in the network. For an Ethernet network to functionproperly, only one active path can exist between two stations. Loops occur innetworks for a variety of reasons. The most common reason you find loops

in networks is the result of a deliberate attempt to provide redundancy - incase one link or switch fails, another link or switch can take ov

W hat is VPN?

A VPN is a service that offers secure, reliable connectivity over a sharedpublic network infrastructure such as the Internet. VPNs maintain the samesecurity and management policies as a private network. They are the mostcost effective method of establishing a virtual point-to-point connectionbetween remote users and an enterprise customer's network.


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W hat is VPN?

Virtual Private network is a network that used the public telecommunicationinfrastructure. This means that it used public wires to connect the nodes.E.g. Internet. VPN supports remote access to computers and allow data tobe transmitted over this public network. Even though the data is transmittedover a public network, encryption and decrypting data to ensure security.

How w ould you def ine I P address?

IP address or Internet Protocol address is the address of a device attachedto an IP network (TCP/IP network). It is a must for every client, server andnetwork device to have a unique IP address for each network connection

(network interface). Every IP packet contains a source IP address and adestination IP address. As a device moves from one network to another, itsIP address changes.

Computers using the TCP/IP for communication are uniquely identified by a32 bit address called as an IP address. The routers use the IP addressinformation to forward the packet to the destination computer.

IP addresses are categorized as:

Private a ddress : these IP addresses are used exclusively within a privatenetwork and not for public to see.

Public Address : these are registered IP addresses used for public.

Each IP address has a network address and a host address. IP addresses areexpressed in four sets of three numbers, separated with dots. Each set iscalled as an octet because when converted to binary; it denotes eightbinary.

Difference betw een Stat ic and Dynamic I P.

Static IP is also called as permanent address assigned to each device in anetwork, whereas Dynamic IP, a temporary address assigned to the devicevia DHCP software. IP address assigned to your service by your cable or DSLInternet provider is typically dynamic IP. In routers and operating systems,the default configuration for clients is dynamic IP

W hat is the difference betw een public and private I P?


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A public IP address allows equipment accessible to everyone on the internet.A private IP address is for private use within the network and allows manymore PCs to be connected. If you are using a private IP and wants VOIP, youneed to change to a public IP address.

W hat is Netw ork Address Translat ion?

Network Address Translation acts as an agent between the Internet and alocal network. It is a dynamic method which is used to minimize Internetconnectivity needs. Network address translation describes the rewriting of the Internet Protocol (IP) addresses of data packets so that multipletransmissions require only one IP address.

Def ine I P mul t icast .

IP multicast technology reduces traffic by sending stream of information tomany recipients at one go. Video conferencing, stock quotas are theexamples based on IP multicast.

W hat is subneting?

Subnet adds one level to the way IP address is represented. It logicallyorganizes the network. For instance, it can logically group computersbelongs to the finance department.

Def ine Address Resolution Prot ocol.

Address Resolution Protocol ARP, is responsible for mapping an IP address toits corresponding physical network address. It is mostly seen on Ethernetnetwork.

Explain Maxim um Transfer Un it , MTU.

MTU specifies the largest amount of data that can be transferred across anetwork.

W hat is Routing Protocol?

Routing protocol is the way to send routing information between any routersin an autonomous system.


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When a source sends a packet to a destination, this packet has a specificpath or route it follows. Different routing protocols are used to find the

shortest path to the destination. The protocols maintain routing tables.Routing tables consist of a set of rules used to determine where thesepackets will travel. When a packet is received, a network device examinesthe packet and matches it to the routing table entry providing the bestmatch for its destination. The packet keeps hopping until it reaches itsdestination.

Explain the st ructure an d use of inter net a ddresses.

Each IP address is 32 bit long. In human language the IP addresses arewritten in dotted decimal notation. These are then converted to binary bythe computer. Each IP address has two parts: Network identifier or anetwork ID and host ID. The current internet protocol standard is IPV4. TheIP addresses are divided into three classes: a class A network, a class Bnetwork, and a class C network. Class A being the largest. The four digitnumbers in an IPV4 address, each network of class A will have different firstnumber, and then its network will be addressed by the rest of the threenumbers, or three bytes. The IP addresses identify a machine to deliverpackets and load web pages.

Explain how name s are t ransla ted ( resolved) into I P address.Domain Name server or DNS is used to resolve names into IP addresses.When a web address is entered into the browser, the DNS client sends arequest to the DNS server to find the corresponding IP address for thename. The DNS server receives this request and searches for thecorresponding IP address in the database. If at this point the resolution fails,this server sends this request to the parent server. The request keeps goingup the hierarchy to the parent servers or the closest authoritative of theDNS server to resolve the address. If the request times out an error isretuned to the client. If the server is able to resolve the name requested, itpasses the information back to the client. The next request sent by the clientis to request for a web page for the IP address.

Describe th e basics of inter net r outing.

When a source sends a packet to a destination, this packet has a specificpath or route it follows. Different routing protocols are used to find theshortest path to the destination. The protocols maintain routing tables.Routing tables consist of a set of rules used to determine where thesepackets will travel. When a packet is received, a network device examines


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the packet and matches it to the routing table entry providing the bestmatch for its destination. The packet keeps hopping until it reaches itsdestination.

Define broadcast doma in.

It is a logical area in a computer network where any computer connected tothe network can directly transmit to any other computer in the domainwithout having to go through a routing device

Bridge vs sw itch

A bridge connects two different LAN networks. A switch is something like you

can connect many computers to a switch and then one computer canconnect to another through the switch. Switch is a unicast one to oneconnection.

W hat is a Router?

A router is a device or sometimes a software in a computer which decidesthe next network point to which a packet should be forwarded to reach itsdestination on Internet. It is usually included as part of the network switchand is located at a gateway, including each point-of-presence on theInternet. The router is connected to at least two networks and determineswhich way to send each information packet based on its understanding of the state of the networks it is connected to.

Def ine gatewa y

A gateway is a network point that provides entrance into another network.On the Internet, a node or stopping point can be either a gateway node or ahost (end-point) node. Both the computers of Internet users and thecomputers that serve pages to users are host nodes. The computers thatcontrol traffic within your company's network or at your local Internet

service provider (ISP) are gateway nodes

W hat i s fi rewa l l?

A firewall is a hardware or software installed to provide security to theprivate networks connected to the internet. They can be implemented inboth hardware and software, or a combination of both. All data entering orleaving the Intranet passes through the firewall which allows only the datameeting the administrators rules to pass through it.


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W hat are the types of f i rew al ls?

Packet Filtering Firewall: This type of Firewall detects packets and block unnecessary packets andmakes network traffic release.

Scree ning Router Firew alls: It's a software base firewall available in Router provides only light filtering.

Com puter- based Firew all : It's a firewall stored in server with an existing Operating System likeWindows and UNIX.

Hardw are base Firew al l: Its device like box allows strong security from public network. Mostly usedby big networks.

Proxy Server: Proxy server allows all clients to access Internet with different access limits.Proxy server has its own firewall which filters the all packet from webserver.

W hat is Data encryption?

Data encryption ensures data safety and very important for confidential orcritical data. It protect data from being read, altered or forged whiletransmission.

W hat is the Pu blic Key Encrypt ion?

Public key encryption use public and private key for encryption anddecryption. In this mechanism, public key is used to encrypt messages andonly the corresponding private key can be used to decrypt them. To encrypta message, a sender has to know recipients public key.

Define Digital Signatures.

Digital signature is an attachment to an electronic message used for securitypurpose. It is used to verify the authenticity of the sender.

W hat is Ethernet technology?


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Ethernet technology is a high speed broadcast bus technology. In this type,all the station shares a single ether channel and receives every singletransmitted signal.

Explain the use of netw ork interface card, NI C.

NIC is used to connect computer to an Ethernet network.

Explain tok en ring technology.

In this technology, all the devices are arranged in a circle. A token movesaround the circular network. A device waits for the token before it sends itsframe. Once it receives token, it initiates transmission of its frame.

W hat is CSMA and CD concept?

In CSDA (carrier sense multiple access), presence of any digital signal in anetwork is checked before transmission. Data transmission occurs only whenno signal is sensed.

CD, Collision detection is responsible for monitoring carrier in order to avoidsignal jam.

W hat is NetBI OS protocol?

NetBIOS (Network Basic Input/Output System) Protocol allows applicationson separate computers to communicate over a LAN. It runs over TCP/IPgiving each computer in the network a NetBIOS name and IP address. E.g. Itcan be used for computers running Windows 2000 (or before) to join acomputer network running Windows 2000 (or later).

W hat is I GMP protocol?

Internet Group Management Protocol, allows internet hosts to multicast. i.e.

to send messages to a group of computers. There may be a group of internet hosts interested to multicast. IGMP allows router to determine whichhost groups have members on a given network segment. It helps toestablish group memberships. It is commonly used for streamlining videosand gaming. The protocol can be implemented both as a host side androuter side. The host side is responsible to notify its membership in a group.The notification is made to a local router. This local router (router side) inturn sends out queries.

W hat i s TCP / I P protocol?


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Transmission Control Protocol / Internet Protocol: - It is a family of protocolsused for communication and connection between hosts on the internet. It isthe most widely used standard for transmitting data over the internet. Thefour layers in the protocol are (from bottom to top):- Physical layer, Datalink layer, Network layer, transport layer and application layer, also called asthe OSI model. In TCP/IP , IP is responsible for forwarding packets while TCPensures the correct delivery of data from client to server. TCP detects loss of data as well.

W hat is HTTP ( Hypertex t Transfer Protocol) ?

HTTP or Hyper Text Transfer Protocol is provides a set of rules to transferfiles, videos, images over the world wide web. When the web browser is

opened, a HTTP request call is made. A web server contains a HTTP daemon.This daemon is used to wait for HTTP requests and handle them when theyarrive. The web browser from where HTTP requests are made is called as aclient. These requests are sent to the server. It uses a reserved port no 80.

W hat i s NNTP ( Netw ork New s Transfer Protocol) ?

NNTP or Network News Transfer Protocol is used to manage the notes postedon Unset newsgroup (a collection of posted notes on a subject posted bydifferent users). NNTP servers are responsible for managing Usenetnewsgroup collected globally. A NTTP client is a part of the web browser alsocalled as a news reader. It uses a reserver port no 119.

W hat is POP3 ( Post Office Protocol 3) ?

POP3 or Post Office Box 3 is used for receiving emails. It is a client serverprotocol which holds the email. Once the email is downloaded from theserver, POP3 deletes it from the server. Ordinal numbers are used to identifyspecific messages.

W hat i s SNMP ( Sim ple Netw ork Management Protocol) ?

SNMP or Simple Network Management Protocol is typically used formanaging the network. Managing the network includes managing the nodespresent in the network. These nodes may be server, routers, bridges andhubs. SNMP agents are used to achieve this. Managing the network isessential because it helps to monitor network performance, detect networkfaults or failures, audit network usage etc. the SNMP messages like TRAP,GET or SET may be invoked by network elements or network managementsystem.


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W hat is Routing table?

A routing table stores the routes of the various nodes in a network. Nodescan be any electronic device connected to the network. The table is usuallystored in a router or the network computer as a database or file. Thisinformation helps to fond the best possible path. The routing table has atleast 3 fields: the destination network id, cost of the path, next hop oraddress to send the packet.

W hat is Routing Protocols?

Routing protocols are used to assist in achieving the basic purpose of routing. They specify the routers the method to communicate with each

other. They help the routers select the best possible path between nodes.There are different types of protocols such as link-state routing protocols,path vector protocols and distance vector routing protocols. These protocolsprevent routing loops to form or break if formed already. They help to decidepreferred routes from a sequence of hop costs..

W hat is Distance Vector Routing Protocols?

The main goal of Distance Vector Routing Protocols Is to find out the bestpath for he data packet to reach the destination. Distance here could be thehops. The three different types of Distance Vector routing protocols include:-Routing Information Protocol (RIP v1 and v2) and Interior Gateway RoutingProtocol. The protocol is easy to manage however not well scalable.

The Distance Vector protocol initially prepares a Routing table which isshared with other routers. This routing table is shared between routerspresent in the same network. A new routing table is prepared when somenew information is received from some other router. Now, the bad routingpaths are removed keeping only the smallest hop paths. This new table isthen communicated to other routers.

Explain Transmission Control Protocol, TCP

TCP ensures reliable and end to end delivery of segments of information.Segments are acknowledged to the source when received by the destination.Data is broken up into segments and sequenced properly beforetransmission. This arrangement of segments allows destination to trace lostdata in transmission.

W hat is TCP protocol?


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Transmission control Protocol is used to establish communication betweennodes or networks and exchange data packets. It guarantees delivery of data packets in the order they were sent. Hence it is most commonly used inall applications that require guaranteed delivery of data. It can handle bothtimeouts (if packets were delayed) and retransmission (if packets were lost).The stream of data is transmitted in segments. The segment header is 32bit. it is a connectionless communication protocol at the third level (network)of the OSI model.

TCP vs. UD P.

TCP guarantees the delivery of data. UDP on the other hand, does notguarantee delivery of data. TCP delivers messages in the order they were

sent. UDP has no ordering mechanisms. In TCP data is sent as a streamwhile UDP sends data as individual packets. UDP is faster than TCP. TCP is aconnection oriented protocol while UDP is connectionless.

Explain User Data gram Protocol , UDP.

The UDP is a connectionless, unreliable service. UDP messages can be lostand duplicated.

W hat is UDP protocol?

User Data Protocol is a communication protocol. It is normally used as analternative for TCP/IP. However there are a number of differences betweenthem. UDP does not divide data into packets. Also, UDP does not send datapackets in sequence. Hence, the application program must ensure thesequencing. UDP uses port numbers to distinguish user requests. It also hasa checksum capability to verify the data.

TCP vs. UD P.

TCP guarantees the delivery of data. UDP on the other hand, does not

guarantee delivery of data. TCP delivers messages in the order they weresent. UDP has no ordering mechanisms. In TCP data is sent as a streamwhile UDP sends data as individual packets. UDP is faster than TCP. TCP is aconnection oriented protocol while UDP is connectionless.

What is TCP windowing concept?

TCP windowing concept is primarily used to avoid congestion in the traffic. Itcontrols the amount of unacknowledged data a sender can send before itgets an acknowledgement back from the receiver that it has received it.


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W hat is Trusted and Untrusted Netw orks?

Trusted netw orks: Such Networks allow data to be transferredtransparently. The machines using a trusted network are usuallyadministered by an Administrator to ensure that private and secured data isnot leaked. Access to this network is limited. Computers using trustednetworks are more secured and confidential because of strong firewalls.

Untrusted networks: Such networks are usually administered by theowners. They can allow improper access to sensitive or personal data. Thesemachines are usually separate. Such machines could me more prone toattacks.

W hat are the different type s of VPN?

Rem ote Access VPN :- Also called as Virtual Private dial-up network(VPDN) is mainly used in scenarios where remote access to a networkbecomes essential. Remote access VPN allows data to be accessedbetween a companys private network and remote users through athird party service provider; Enterprise service provider. E.g Salesteam is usually present over the globe. Using Remote access VPN, thesales updates can be made.

Site to Site VPN Intranet based: This type of VPN can be usedwhen multiple Remote locations are present and can be made to jointo a single network. Machines present on these remote locations workas if they are working on a single network.

Site to Site VPN Extranet based: This type of VPN can be usedwhen several different companies need to work in a sharedenvironment. E.g. Distributors and service companies. This network ismore manageable and reliable.

W hat a re the different aut henticat ion m ethods used in VPNs?

The authentication method uses an authentication protocol. The methods

are:

EAP authent icat ion m ethod: Extensible authentication protocolauthenticates remote access connection. The authenticationmechanism is decided between the remote VPN client andauthenticator (ISA). The mechanism is typical in which authenticatorrequests for authentication information and the responses are given bythe remote VPN client.

MS Chap Authenticat ion m et hod: Microsoft Challenge HandshakeAuthentication Protocol (MS-CHAP) starts with the authenticator


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(Remote access server) challenge. The challenge to the remote accessclient sends a session identifier and challenge string. The client inresponse sends the nonreversible encryption of the string, theidentifier and password. Authenticator checks the credentials andgrants access on a successful authentication.

Unencrypted passw ords ( PAP) :- Uses plain text passwords. Doesnot involve encryption. Used for less secure clients.

Shiva Passw ord Authen tication Protocol ( SPAP) :- It is apassword authentication protocol. It is less secure as the same userpassword is always sent in the same reversibly encrypted form

W hat is Tunneling?

Tunneling is a mechanism provided to transfer data securely between twonetworks. The data is split into smaller packets and passed through thetunnel. The data passing through the tunnel has 3 layers of encryption. Thedata is encapsulated. Tunneling can be approached by Point to Pointtunneling protocol.

W hat a re voluntary and com pulsory tunnels?

Voluntary Tunneling Users computer is an end point of the tunnel and acts as tunnel client. Herethe client or user issues a request to configure and create a voluntarytunnel. They require a dial up or LAN connection. Example of dial upconnection is internet at home where a call is made to the ISP andconnection is obtained.

Compulsory tunneling In compulsory tunneling, instead of the user a vpn remote access serverconfigures and creates a tunnel. Hence, the end point is the Remote severnot the user.

Explain stat ic an d dynam ic tun nels.

Tunnels that are created manually are static tunnels. Tunnels that are autodiscovered are dynamic tunnels. In dynamic tunneling, tcp connections canbe checked dynamically. If no connections exist that are routed through thetunnel, a check for more suitable gateway can be done. Static tunneling mayat times require dedicated equipments.

Explain th e im porta nce of increasing and decreasing subnet bits.


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Adding 1s as a bit means increasing the subnets and decreasing the hosts.Removing or decreasing 1s means decreasing subnets and increasing hosts.Hence by increasing or decreasing the subnet architecture can be decided asper needs.

W hy do we need a subnet m ask?

A subnet mask allows identification of host part and network part of an IPaddress. Subnet mask can be used to find if an IP address is present on asubnet or not.

W hat is RTP?

Real-Time Transfer Protocol lays a standard or a way to transfer or managereal time data over a network. It does not guarantee the delivery of data orprovide any quality of service. However it helps to manage the data. Whichmeans that RTP can be used deliver the necessary data to the application tomake sure it can put the received packets in the correct order Real time dataexamples could be audio and video.

What is RTP Multiplexing?

RTP multiplexing allows multiple media flows within a single RTP datapayload between two points. This means that it can be used to carry multiplestreams of data in one RTP packet. RTP multiplexing will reduce thebandwidth used. RTP multiplexing will also increase scalability

Explain the use of RTP an d RTCP protocols.

Use of RTP and RTCP:-

1. RTP can be used to transfer Real time data like voice packets.2. RTP can be used with RTCP which makes it possible to monitor data.3. Packet loss can be detected by RTP using Sequence number

RTCP provides Qos feedback :- Packets lost, round trip time.

Describe th e form at of RTP and RTCP packets.

The 32 bits of RTP packet format is as follows:- (L to R)

Bit 0-1:- Indicates version, currently 2Bit 2:- P- indicates padding bytesBit 3:- X- Indicates presence of extension header


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Bit 4-7:- CC- Contains number of CSRC identifiers that follows the headerBit 8:- M- Current data has some special relevance (if set)Bit 9-15:- PT- Indicates format of payloadBit 16-31:- Sequence numberTimestamp: - 32bits time stamp of packetSSRC- Synchronization source identifier uniquely identifies the source of astream.CSRC -Contributing source IDs enumerate contributing sources to a streamwhich has been generated from multiple sourcesExtension header: - first 32 bit word contains profile specific identifier andlength specifier

The 3 2 bits of RTCP header form at is as follows:- ( L to R)

Bit 0-1:- Indicates version, currently 2Bit 2:- P- indicates padding bytesBit 3 to 7:- Count of number of reception report blocksBit 8 to 15:- Type: - Determined RTCP packet type. Type can take valuesfrom 0 to 25516 to 31:- Length- Length of RTCP packet - 1SR: - Sender Report for transmission and reception from active sendersRR: - Receiver report for reception from in active sendersSDES: - Source description itemsBYE- indicates end of participationAPP: - Application specific functions

Describe how the mult icast protocol w orks.

Multicast protocol or Internet protocol delivers a singles message to multiplemachines. One packet from the source is replicated and sent to thedestination. Every multicast message requires a multi case group. The groupdefines the addresses which will receive the message. The group is definedby the class D address. Different routing protocols are used to find themulticast groups and build routes for them. Distance Vector Multicastprotocol is one of them. The receiver, to whom the multicast packet is sent

to, needs to join the group. Joining the group is enabled and managed byIGMP. Multicast routers are used to transmit the messages from one networkto another.

Describe how to control the scope of m ulticast t ransm issions.

Controlling the scope of multicast transmission restricts the range of groupmembers. TTL (Time To Live) is one of the mechanisms to limit the scope. If the TTL value is small, packets would only be multicast to smaller distancedestinations. More the value of TTL, more would be the scope of


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transmission to a larger number of machines. Administrative scoping isanother mechanism. In this, transmission is restricted to a specific addressspace of an organization or a site.

Explain why use Multicasting.

When the same message or packet needs to be sent to multipledestinations, multicasting is used.

Within campus and offices, using multicasting file distribution can bedone.

System messages, news and videos can be sent at the same time. More commonly used for audio and video streaming.

W hat is a socket?

A socket is used to connect an application to a network protocol. A socketenables communication between a client and a server. The communication isstarted when the client is assigned a local port number, and binds a socketto it. The client writes on the socket and gets information from server byreading it.

W hat a re Sockets? How do Sockets W ork?

A socket is used to connect an application to a network protocol. A socketenables communication between a client and a server. The communication isstarted when the client is assigned a local port number, and binds a socketto it. The client writes on the socket and gets information from server byreading it. The Socket class is used to communicate. It provides rich set of methods for both asynchronous and synchronous data transfer.ConnectAsynch is used to start an asynchronous connection. SendAsynchand ReceiveAsynch are used to send and receive data. Shutdown and closemethods are used to shutdown and close the sockets.

Datagram vs. st ream .

Stream can be considered as a pipe that allows full duplex connection. Adatagram or a packet on the other hand, has a source and a destination.There is no connection. Stream is like a communication channel whiledatagram is completely self contained. Streams provide a reliable andsequenced communication. Datagrams on the other hand are unreliable andno sequence maintained.

W hat is a stream socket ?


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A stream socket provides two way communications between a client andserver. This communication is reliable and sequenced. Stream sockets areabove TCP to run across any networks. They provide unduplicated flow of data and have well established mechanism for creating and destroyingconnections and for detecting errors.

W hat is SSL?

SSL is Secured Socket Layer. SSL is used to establish a secured and anencrypted connection between a server and the browser. SSL is mostcommonly seen in payment and banking web sites. To create a SSLconnection, a SSL certificate needs to be created. If the website has a SSLcertificate installed, a small icon is displayed in the tool bar to make

customers confident that the site is secured.

W hat are the t w o im portant TCP Socket classes? Explain them

The two most important socket Classes are:

Socket Class: The Socket class provides enriched methods andproperties for network communications. It allows both synchronousand asynchronous data transfer. Shutdown method should be used toend the Socket once the data transfer is complete. UsingSetSocketOption the socket can be configured.Declaration:

Public Class Socket _Implements IDisposable

Server Socket Class: The server Socket class is used to implementserver sockets. Server sockets are used to respond to requestsreceived over the net

W hat are the a dvantages and disadvantages of Java Sockets?

Advantages:

Flexible and powerful. Cause low network traffic if efficiently used. Only updated information can be sent.

Disadvantages:

The Java applets can establish communication only with the machinerequested and not with any other machine on the network.


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The use of 56-bit keys: 56-bit key is used in encryption, there are 256possible keys. A brute force attack on such number of keys isimpractical.

The nature of algorithm: Cryptanalyst can perform cryptanalysis byexploiting the characteristic of DES algorithm but no one hassucceeded in finding out the weakness.

Weakness- Weakness has been found in the design of the cipher:

Two chosen input to an S-box can create the same output. The purpose of initial and final permutation is not clear.

f you are a vict im of Denial of Service ( Dos) then w hat you do?

The function of a denial of service attack is to flood its target machine withtoo much traffic and prevents it from being accessible to any other requestsor providing services.

To prevent DoS attacks firewall can be configured as a relay; in thisapproach the firewall responds on behalf of the internal host. Duringthe attack, the firewall responds to the SYN sent by the attacker; sincethe ACK never arrives, the firewall terminates the connection.

By Keeping protocols and Antivirus software up-to-date, we canprevent to be a victim of DoS. A regular scanning of the machine isalso necessary in order to detect any anomalous behavior.

W hat a re Brute Force Attacks?

Brute forcing is a mechanism which is used by an attacker to break theencryption of data by applying a set of various key. Cryptanalyst has a set of number of keys and apply them one by one to the encryption algorithm untilhe get the right key.

Example: http://www.xxxxx.com/online/Displaymsg.asp?msgID=78961

In this example a cryptanalyst may apply bruteforcing to the value of msgIDand read the users data.In this the browser requesting for Displaymsg.asp page and sending msgID78961 to the web server.

How do you use RSA for both a uthe nt icat ion and secrecy?

RSA is a public key encryption algorithm. The RSA algorithms are based onthe mathematical part that it is easy to find and multiply large prime


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numbers together, but it is extremely difficult to factor their product.

For authentication: One can encrypt the hash (MD4/SHA) of the data with aprivate key. This is known as digital signature.

For Secrecy: Secrecy/confidentiality is achieved by encrypting the data withpublic key and decrypting with private key.

Can you differentiate among encoding, encryption and hashing?

Encoding: Basically encoding is used to protect the integrity of data as itcrosses through communication network to keep its original message uponarriving. It is primarily an insecure function because it is easily reversible.

Encryption: Encryption is basically designed for confidentiality and dataintegrity and reversible only if you have the appropriate key.

Hashing: With hashing the operation is one-way i.e. non-reversible. It takesan input (or message) and returns a fixed-size string, which is called thehash value.

I f you have to generate a hash function then w hat character ist icsare ne ede d in a secure ha sh function?

A secure hash function should have the following characteristics:

i. The output generated by a hash function should be of a fixed length.

ii. It should be very easy to find out a hash function for a given message.

iii. If a hash value is given of a message than it is almost impossible to getthat message.

iv. The two different messages should not have the same hash value; it is

against the hash function property.

W hat is digital signature ? Differentiate betw een Physical and DigitalSignature

A digital signature is an electronic analogue of a written signature; thedigital signature can be used to provide assurance that the claimed signatorysigned the information. Digital signature is used to detect the integrity of signed data. We can differentiate between physical and digital signature as:


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i. Physical signature is just writing on paper but digital signature includescrucial parameters of identification.

ii. Physical signature can be coped but it is impossible to copy a digitalsignature.

iii. Physical signature does not give any privacy to content but digitalsignature enables encryption and thus privacy.

W hat is Authent icat ion Heade r and how i t provides the protect ion toI P header?

Basically Authentication Header protects IP header and provides thecomplete authenticity to the IP packets.

AH may work in two ways: transport mode and tunnel mode.

In tunnel mode; AH protects the IP header using two IP header layers innerand outer. Inner IP header is used to contain the source and destinationaddresses, and the outer IP header is used to contain the security gatewayinformation.

Explain SSL Protocol. How does it prote ct interne t users from variousthreats?

The SSL protocol (Secure Socket Layer protocol) was originally developed byNetscape, to ensure security of data transported and routed through HTTP,LDAP or POP3 application layer.

SSL uses TCP as a communication layer to provide a reliable end-to-endsecure and authenticated connection; which helps internet users to protectfrom various threats. SSL Record protocol is used to ensure the data security

and integrity.

W hat is PI X f irew all securi ty? How does i t differ from a f ire w all?

PIX (Private Internet Exchange)

It is a popular IP firewall and NAT (Network Address Translation) appliance.

PIX firewall security is developed by Cisco Systems.


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PIX firewall is used to protect your network with a stateful packet filteringfirewall.

A firewall is a part of a computer system or network that is designed to blockunauthorized access while permitting authorized communications.

W hat are Ma lwa re? Explain different t ypes of Malw are

Malware is a software program which is developed to destroy a computersystem. These programs runs in victims computer without any informationto the victim, i.e. victim do not know that someone hacked his system.

Different types of malware are: worm, Trojans Horse, Rootkits.

Worm: Worm is a computer program which makes its copy again and againin the victims computer. They damage the network by using a lotbandwidth.

Trojan Horses: Trojan horse consists of two parts, server and client. Serveris an executable file which runs on victims computer and attacker may takethe full control of the victims computer.

Rootkits: Rootkits are used to hide the malicious processes from activeprocess

W hat a re replay at ta cks? Give an exam ple of replay at t ack

Replay attacks are the network attacks in which an attacker spies theconversation between the sender and receiver and takes the authenticatedinformation e.g. sharing key and then contact to the receiver with that key.In Replay attack the attacker gives the proof of his identity and authenticity.

Example:

Suppose in the communication of two parties A and B; A is sharing his keyto B to prove his identity but in the meanwhile Attacker C eavesdrop theconversation between them and keeps the information which are needed toprove his identity to B. Later C contacts to B and prove its authenticity.

I f you have to encrypt as w ell as com press data duringtra nsm ission then w hich w ould you do f irst and w hy?


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Data should be transmitted over any communication network in such a waythat the data integrity and authenticity should be maintained, for this firstcompress the data and then encrypt the data.

The reason behind it is; if you encrypt first you will have nothing but randomdata to work with, which will destroy any potential benefit fromcompression.

W hat is the goal of I nformat ion Securi ty in an organization?

Mainly there are three Information security goals in an organization:Confidentiality, Integrity and Availability.

Confidentiality: Confidentiality means maintaining secrecy duringtransmission of information.

I n tegri ty : Integrity means changes made in the stored information need tobe done only by authorized entities and through authorized mechanism.

Availability: Information is useless if it is not available. Availability meansinformation created and stored should be available to authorized entities.

W hat is Symm etr ic- Key cryptography and Asym m etric-Keycryptography?

Symm et ric-Key Cryptography: Symmetric-key cryptography uses a singlekey for both encryption and decryption. Encryption and decryption algorithmare inverse of each other.

Example:

To create the ciphertext from the plaintext John uses an encryptionalgorithm and a key. To create the plaintext from ciphertext, Bob uses the

decryption algorithm and the same key.

Asym m etric- Key cryptography: It is also called public key cryptography.In public key cryptography two keys: a private key and a public key is used.Encryption is done through the public key and decryption through privatekey. Receiver creates both the keys and is responsible for distributing itspublic key to the communication community.

Example:


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The sender (say John) uses the public key to encrypt the plaintext intociphertext and the receiver (say Bob) uses his private key to decrypt theciphertext.

Explain the services provided by I P ( I nter net Protocol) - Addressing,Fragment at ion, Packet t im eouts and options

1 . Addressing: For the purpose of delivering datagram packets, IP needs toknow about the address of the destination. By including the host addressing,this task is carried out by IP. As IP operates in an internet, its systems aredesigned to accept the addressing of devices which are unique.

2 . Fragment ing: The datagram packets are sent to the data link layer for

the purpose of transmission on the network. The physical network frame sizethat uses IP may be different. To resolve this, IP fragments the datagraminto certain pieces. So that, each piece can be carried on the network. Thereceiving systems use these pieces and reassemble the whole IP datagramagain.

3. Packet t im eouts: A timeout packet is the time for waiting nextinstruction from the command station. If the command is not sent by thestation, it shuts down.

Explain th e classes of I P address

IP addresses are organized into classes. For convenience of humans, IPaddresses are expressed in the decimal format. Every number in each classis represented as binary to computers.

The four numbers in an IP address are known as octets. Each of them haseight bit positions. The octets are divided into two sections: Net and Host.The first octet represents Net for identifying the network and the Hostcontains the last octet. There are five IP classes.

Class A: The class A is used for very large networks. There are 1 to 126 arepart of this class. That means there are 126 Class A networks. Class Anetworks accounts for half of the total available IP addresses.

Class B: It is used for medium size networks. The IP address with a firstoctet from 128 to 191 is part of this class. Class B networks have a first bitvalue of 1 and a second bit value of 0 in the first octet.


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Class C: Class C is used for small to middle size networks. IP address with afirst octet starts from 192-223. Class C networks have a first bit value of 1,second bit value of 1 and a third bit value of 0 in the first octet.

Cla ss D: It has first, second and third bit value as 1 and the fourth bit as 0.The other 28 bits are used for identifying the group of computers which isintended for multicast messages.

Class E: Class E is used for identification purpose. The four bits value is 1.The other 28 bits are used for identifying the group of computers which isintended for multicast messages.

Def ine Broadcast, Unicast an d Mult icast.

Unicast: A term used in communication to describe a piece of information tosend from one point to another. There are only sender and receiver. All LANssupport unicast transfer mode and most applications that employ TCPtransport 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 andmultiple receivers. All LANs support broadcast transmission.

Multicast: A term described in communicating a piece of information sentfrom one or more points to a set of other points. The senders and receiversare one or more.

W hat i s Netw ork Mask?

A network mask is used for determination of what subnet an IP addressbelongs to. An IP address has network address and the host address. Thefirst two numbers represents the network address and the second twonumbers represents the host of the network.

Define Subnett ing.

A subnet describes a set of networked computers which have common IPaddress routing prefix.

Breaking the networking into smaller and more efficient subnets is known assubnets. Subnetting prevents Ethernet packet collision which has excessiverates in a large network. Routers are used to manage the traffic andconstitute borders among subnets.


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W hat i s the User Data gram Protocol ( UDP)?

User datagram protocol allows computer applications to send messages asdatagram packets from source to destination on an Internet Protocol, without using prior communications for setting up special transmission paths. Anunreliable service is provided by UDP which makes the datagram packetsmay arrive irrespective of order. UDP is a better solution for time-sensitiveapplications due to the reason dropping packets is preferable to use delayedpackets. Its stateless nature makes the server to answer smaller queries tohuge number of clients.

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