Top OSI Model Interview Questions and Answers [CCNA] 2019

In this post, we will be discussing the OSI Model Interview Questions and Answers (CCNA). OSI is the conceptual and reference model which standardize how the communication between the computer systems/applications take over the network.

So. Let’s begin with the most important and recently asked Interview Questions on basis of tech experts.

1. • 1. What is OSI Layer Model?

        OSI is the Open Systems Interconnection is a reference model which defines the standards of communication between the computer systems/applications over the network. It is not implemented in the real world but taken as the reference to how computers communicate with each other using various protocols defined in each layer. There are 7 layers in the OSI model.

     2. List the layers of OSI Model?

        There are 7 layers in the OSI model i.e. :
        1. Application Layer
        2. Presentation Layer
        3. Session Layer
        4. Transport Layer
        5. Network Layer
        6. Data Link Layer
        7. Physical Layer

         

         

        

     3. Is there any other alternative model to the OSI model? If yes, explain it.

        We have TCP/IP as an alternate model which also explains the standards of communication between computers/application over the network. It is a much more simple model as compared to the OSI layer model and also contains fewer details of protocols than the OSI model.

        TCP/IP model has 4 layers whereas the OSI model is 7 layer architecture model. The 4 layers of the TCP/IP model are Application Layer, Transport Layer, Internet Layer, Network Access Layer.

        

        TCP-IP Model vs OSI Model

     4. Explain the difference between TCP and UDP?

        Comparison chart between TCP and UDP protocols

         

        

        Difference between TCP and UDP

         

     5. Explain the functions of Data Link, Network and Transport Layer?

        Data Link Layer

        a. It is the second layer of the OSI model.
        b. It is responsible for the physical transformation data. It ensures the message delivery to the right device on the basis of the MAC address.
        c. It helps in generating error notification and flow control.
        d. It provides services to the upper layer i.e. Network Layer by transforming packets into frames.
        e. Data link layer adds the customized header into the messaging which contains hardware source and destination MAC address.

        Network Layer

        a. It is the third layer of the OSI model.
        b. It manages the network devices on the basis of IP address.
        c. It is responsible for packet forwarding, routing and addressing.
        d. It transmits data segments between networks in the form of packets.
        e. It also determines the best path for the packet delivery between the Source IP Address and Destination IP address.

        Transport Layer

        a. Transport Layer is the fourth layer of the OSI model
        b. It receives data from the Session Layer and segments it.
        c. Each segment is made up of Source and Destination Port number, Protocol/Services and Sequence number.
        d. Transport layer has two well-known protocols— TCP and UDP.
        e. It performs error checking. If any data segment is lost, it re-transmits the same.
        f. It provides the feature of Data Integrity by maintaining flow control.

         

     6. Explain the Physical Layer of the OSI model?
        

        a. It is the 1st layer of the OSI model.
        b. It converts the binary data received from Data Link Layer into signals and transmits them over the local media which can be electrical signals, light etc. depending over the local media.
        c. All the hardware such as NIC, Ethernet, ADSL, Bluetooth are the protocols of Physical Layer.

         

     7. What is the difference between Half-Duplex and Full-Duplex?

        Half-Duplex: In half-duplex data can travel in both directions but not at the same time. Either device can send the data or can receive the data at a single point of time.

        Full-Duplex: In Full-Duplex scenario, Data can travel in both direction at the same time. Data can travel in both directions simultaneously.

     8. Explain the difference between Flow Control and Error Control?

        Flow Control: Flow Control is the function of adjusting the flow of data from one device to another device in between adjacent OSI layers. It is used for ensuring that receiving device can handle all incoming data. It is particularly used when sending device is capable of transmitting the data as a much faster rate as compared to receiving a device.

        Error Control: Error Control is the process of detecting and controlling the errors which arrive during the transformation of data both the bit level and packet level errors.

        During the transformation of data from one computer/application to another involves many steps, each step can subject to error. With the Error Detection and Error Control process we can be that the transmitted and received data is identical.

     9. List the different protocols works at each layer of the OSI model?
        

        1. Application Layer Protocols:

        Telnet, FTP, TFTP, SMTP, DNS, BOOTP, SNMP, CMOT

        2. Presentation Layer Protocols:

        Apple Filing Protocol (AFP), Independent Computing Architecture (ICA), Lightweight Presentation Protocol(LPP), NetWare Core Protocol(NCP), Network Data Representation(NDR)

        3. Session Layer Protocols:
        

        Apple Talk Data Stream Protocol (ADSP), Apple Talk Session Protocol (ASP), H.245, Layer 2 Forwarding Protocol (L2F), NetBIOS, PAP, PPTP, RPC, RTCP, SMPP, SCP, SOCKS, ZIP, SDP

        4. Transport Layer Protocols:

        TCP, UDP, SST, SPX, SCTP, RUDP, MPTCP, FCP, CUDP, ATP

        5. Network Layer Protocols:

        IPv4, IPv6, RIP, EIGRP, ICMP, IGMP, EGP, DDP, CLNS, IPSec, IPX, PIM

        6. Data Link Layer Protocols:

        Ethernet, CDP, ATM, ARCnet, CAN, Econet, EAPS, FDDI, Frame Relay, HDLC, LAPD, LLDP, PPP, NDP, SpaceWire, Token Ring, MPLS

        7. Physical Layer:

        Analog Transmission, Asynchronous Serial Communication, IEEE802.3, Repeater, Circuit switching, Serial Communication, Passband, PHY, PhoneNet, Modem, CoaXpress

        Top 50 Networking CCNA Interview Questions & Answers?

     10. What is Port Number and Define the Range of Port Numbers?

         A port number is a unique identification 16-bit unsigned number that is put in a header appended to a message unit. They identify a specific process or network services.
         When any message is received by the server or endpoints, it needs the mechanism to identify for forwarding the message to right process, to identify the process we use the Port Numbers.

         The range of Port Numbers:
         a. Well Known Ports: 0 to 1023
         b. Registered Ports: 1024 to 49151
         c. Private or Open Ports: 49152 to 65535

          

     11. Difference between Data Encapsulation and Data de-encapsulation?
         
         When data is transfer from the higher layer to the lower layer. Each layer adds its header to the original packet. This is known as Data Encapsulation.
         
         When data is transferred from the lower layer to the higher layer, each layer removes the information added by the other layers. It will remove the headers added by other layers and will insert its own header. This is known as Data de-encapsulation.
         
     12. What is CRC? On which layer CRC works?
         
         CRC is Cyclic Redundancy Check. It is used to detect errors in a network. It works at Data Link Layer.
     13. What is TCP Three-Way Handshake?
         
         A TCP Three-way Handshake is a method to establish a connection between the client/localhost and server. It has three steps in which client and server exchange their SYN and ACK packets before data transfer take place.