CCNA Interview Questions

CCNA Interview Questions

Q. What is OSI reference model “network” layer?

Network layer is layer 3 of the OSI reference model that defines logical addressing, routing and path determination. Examples of the protocols working at this layer are IP and IPX.

Q. Which of the below are Transport layer protocols?

  1. a) TCP
  2. b) HTTP
  3. c) IP
  4. d) UDP

A: a.TCP, d. HTTP

Q. In networking terminology, what is “data encapsulation”?

Data encapsulation is the process of putting headers and trailers around the data. Each layer encapsulates the upper layer’s data into a new header and trailer. This process is repeated until reaching layer 1 which is responsible for transmitting the data over the transmission medium.

Q. Inwhich OSI reference model layer does HTTP operate?

  1. a) Transport layer
  2. b) Network layer
  3. c) Application layer
  4. d) Physical layer

A: c.Application layer

Q. What is CSMA/CD and how does it work?

When the data transmitted by two or three nodes on a network through the cable, there occurs collision. So, CSMA/CA(Carrier Sense Multiple Access/ Collision Avoidance) is used,

Before transmitting the data on the cable, NIC (network Interface Card) checks the cable if any transmission is going on. If no, sends the data or waits for the transmission to finish.

If two MC senses the medium at the same time, and send the data there occurs collision. Then the node detects the collision and sends a ‘Jam Signal’ to all other nodes on that network.

Q. What are the two kinds of transport possible and give some example?

a) Reliable and unreliable are the two kinds of transport possible

b) The transport varies according to the application

c) The reliable protocol is defined by TCP

d) The unreliable protocol is defined by UDP Example UDP is used in SNMP


UDP is used in SNMP

TCP is used in HTTP

Q. How TCP ensures a reliable as well as controlled transport?

a) The reliable transport is ensured by the assurance of data delivery

b) The controlled transport is ensured by congestion control which means when the resources are busy it does not send the data

Q. For an inherent requirement application which protocol would be better to use at the transport layer?

TCP protocol would be better to use because it resend the acknowledgement when the packet is not received

Q. When the client will declare that the server is unreachable if the client sends data to a server?

a) Even though the server does not send an acknowledgement, the client will not declare the server that it is unreachable. Instead, it resends the data packet until it reaches its threshold value. Declares that the server is unreachable

b) If the client does not receive any acknowledgment after reaching its threshold value, then it declares that the server is unreachable

Q. Why the windowing concept is introduced in TCP?

In TCP, an acknowledgement is sent every time when a fragment of data is received. This increases the traffic when a large amount of data is sent. To avoid this, the Windowing concept is introduced.

Q. List the TCP/IP port for following:

  1. a) FTP
  2. b) TELNET
  3. c) HTTP
  4. d) SNMP
  5. e) POPS

A: FTP-21, TELNET-23, HTTP-8o, SNMP-25, POP3-no

Q. What are the advantages of UDP over TCP?

a) Both are transport layer protocols.UDP is a connectionless protocol while TCP is a connection oriented protocol

b) UDP provides low overhead data delivery than TCP

c) UDP find applications in the Domain Name System (DNS) , Video Streaming , Voice over IP (VoIP) whereas TCP has applications in Web Browsers ,E-mail , File Transfers.

Q. Which connector type is used in Ethernet cables?

a) Rhi

b) RJr2

c) RJ55

d) RJ45

A: d. RJ45

Q. What is broadcast MAC address and what is its value?

The broadcast MAC address is a type of layer 2 addresses that is used to deliver data to all devices in the same broadcast domain of the sender. The source sends only one frame on the network and the switch replicates it to all ports in the same broadcast domain of the source. The broadcast MAC address has a value of FFFF.FFFF.FFFF.

Q. Describe “twisted” pair cables and mention why they are twisted?

Ethernet cables contain 8 wires in 4 pairs groups. Each pair is twisted so that the magnetic field created by one wire cancels out the magnetic field created by the other wire. This enhances performance and decreases transmission noise.

Q. Describe how you can make an Ethernet cross-over cable?

Ethernet cross-over cable is created by connecting Pins 1 and 2 on one side of the cable to pins 3 and 6 on the other side. The other pins’ connectivity doesn’t matter as the  network device uses only 4 wires of the 8 to send and receive data.

Q. What typical cable type do you use to connect two switches together?

a) Straight-through cable

b) Roll-over cable

c) Console cable

d) Cross-over cable

A: d. Cross-over cable

Q. What is the maxinnun cable length in Fast Ethernet (IEEE 8o2.3u) standard?

a) 100m

b) 200m

c) 50m

d) 500m

A: a. 100 m

Q. What is the speed of E1 line?

a) 64 kbps

b) 1.544 Mbps

c) 2.048 Mbps

d) 1.026 Mbps

A: c. 2.048 Mbps

Q. Which of the below are OSI layer2 WAN protocols?


b) PPP

c) Frame-relay

d) Ethernet A

A: HDLC, PPP, Frame-relay

Q. Which of the below are types of Digital Subscriber line (DSL)?






Q. What is ATM?

ATM (asynchronous transfer mode) is a dedicated-connection switching technology used for WAN links. ATM organizes digital data into “cell” units and transmits them over a physical medium using digital signal technology.

Q. When connecting to internet, which of the below remote access technologies are considered always on?


b) Cable Modems

c) Analog modems


A: ADS, Cable Modems, HDSL

Q. You use a DSL connection at home for internet connectivity. You use an IP address of on your PC. The DSL is doing NAT for your IP to to access internet. According to NAT terminology, what is the name of your IP address after being NATed to the public IP as viewed on internet?

a) Inside local

b) Inside global

c) Outside local

d) Outside global

A: b. Inside global

Q. Which protocols below are lave= protocols that can be used over WAN?

a) PPP




A: a. PPP, c. HDLC

Q. Which command below do you use to configure PPP on a serial interface?

a) use ppp

b) set ppp

c) encapsulation ppp

d) protocol ppp

A: encapsulation ppp

Q. When configuring Internet Access Router in small office, which features below are usually configured to allow internet access for users?

a) PAT

b) BGP


d) Telnet

A: a.PAT , c. DHCP

Q. Why PAT is used when configuring SOHO routers?

PAT (Port Address Translation) is a NAT type in which each computer on LAN is translated to the same IP address, but with a different port number assignment. Small Office/ Home Office (SOHO) routers are used in small offices to connect users to internet. It uses one public IP address for internet access. So PAT is used to translate user’s IP addresses to this public IP.

Q. Describe the routing process on the router from the point a packet enters one interface till it exits from another one.

The router checks the destination IP of the packet then it tries to find a match for the destination in its routing table. If a match is found the router gets the next hop IP from the routing table along with the outgoing interface. It then sends an ARP request to get the MAC address of the next hop. It encapsulates the packet into a frame with the router’s MAC address as the source MAC and the next hop MAC address as the destination MAC. Then the router sends the frame out of the outgoing interface.

 Q. Which of the below are class B network addresses?





A: b., c.

 Q. What are the default IP address classes? What are their ranges?

The three default network classes are called A, B, and C

Class A: to

Class B: to

Class C: to

Q. What is a routing protocol?

A routing protocol is a protocol that specifies routers’ communication messages with each other in order to exchange routing information and updates. This information enables the routers to select routes between any two nodes on a network to transport user data.

Q. Describe “classless” addressing.

Classless addressing is an addressing method in which the routing process considers the network and subnet parts of the address together without the rules of Class A, B, and C addressing. This addressing system calls for eliminating the notion of address classes entirely, creating a classless addressing scheme allowing the subnet boundary to move to the right, into the network portion. This mandates sending the subnet mask in the routing updates between the routers.

Q. Describe IP routing protocols mentioning three functions of them.

The routing protocols are responsible for exchanging routing updates between routers. Routing protocols’ functions include:

a) Dynamically learn and fill the routing table with a route to all subnets in the network

b) When multiple routes are learned for a network, select the best route or load balance the traffic over them

c) Notice when routes in the table are no longer valid, and remove them from the routing table d) Prevent routing loops

Q. This IP address belongs to which address class?

Since the beginning of the IP address falls between 128 to 191.This IP address belongs to address class B.

Q. Write the network Address of this IP address and also identify its class. 

a) The network address of the given IP address is

b) And the IP’s range falls between 192 to 223, hence it comes under the ‘class C’

Q. What are the steps involved in computing ‘Address Assignment’?

Following calculations should takes place in the same order:

  1. Broadcast Address
  2. Lowest Host Address
  3. Host Address Range
  4. Network Address
  5. Highest Host Address

Q. How address is dynamically assigned to host?

Using the DHCP method, IP address can be automatically assigned to a host. It does not need to be manually updated. DHCP uses the address pool to assign address to the client. Also assigned address can be reused if the host is powered down or taken out of the network. This feature is favored for mobile users.

Q. Which protocol below allows network hosts to resolve network IPs of other hosts knowing their hostnames?


b) DNS


d) ARP

A: b.DNS

Q. What is TCP Error Recovery?

TCP error recovery serves in detecting transmission errors and recovering them. Using Sequence Number field in one direction combined with the Acknowledgment field in the opposite direction, it detects and retransmits packets with errors.

Q. Which of the below are functions of TCP protocol?

a) Error recovery

b) Encryption

c) Flow control using windowing

d) NAT

A: a. Error recovery, c. Flow control using windowing

Q. Which of the below protocols use TCP as their transport protocol?



c) FTP

d) IP

A: b. HTTP, c. FTP

Q. Describe TCP connection establishment and termination processes.

TCP is a connection oriented protocol. To establish a connection, TCP performs three-way handshaking in which the source sends a SYN packet, the destination sends a SYN/ACK packet and then the source sends ACK packet.TCP terminates connections using the four-way termination sequence using the FIN and ACK flags in which the source sends FIN/ACK packet, the destinations replies with ACK packet, the destination sends FIN/ACK packet and then the source replies with ACK packet.

Q. Why UDP is suitable for VOIP traffic?

Voice data is extremely sensitive to time and greatly benefits from the fast transportation which is associated with the UDP because its headers don’t have any kind of reliability and for practical purposes do not require a guarantee that data is transmitted which enhances usage and speed of VOIP. Hence UDP is suited for VOIP traffic.

Q. What is the DoS attack?

Denial of service (DoS) attacks flood the network with packets to make the network unusable, preventing any useful communication with the network’s users and servers.

Q. What is Spyware?

A spyware is a virus that looks for private or sensitive information, tracking what the user does with the computer, and passing the information back to the attacker in the Internet.

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