Top 50 CCNA Interview Questions and Answers

CCNA is a certification that proves your ability to understand, use, and manage Cisco networks. The CCNA certification provides you with the skills necessary for optimizing and administering Cisco networking resources in an organization. With this credential, you can move on to higher-level certifications such as the MCSA or MCDBA. 

The benefits of obtaining CCNA include:

• Improved job prospects: A well-rounded CCNA certification indicates that you have knowledge about network technologies and their applications – two important factors when seeking employment in information technology (IT) fields.  
• Increased knowledge base: Knowing how to administer Cisco networks allows IT, professionals, more flexibility when deploying systems within an organization, they no longer need someone who only understands hardware configurations.

In this article, we will see the top 50 CCNA interview questions with their answers. 

1. Name any two ports of Switches. 

• Access Port: An access port is a kind of connection on a switch that can be used to connect a virtual machine on VLAN unaware. This port delivers the virtual machine with connectivity by a switch that is VLAN aware without requiring it to support VLAN tagging.
• Combo Port: These ports are used to connect devices to the switch. Switches are connected to a port that is called a combo port. These ports can be assigned to different combinations of devices. A device combination is a group of one or more devices used to transmit or receive data. In other words, a combo port can be a single interface with two front ends, such as an RJ45 connector and an SFP module connector (also called MiniGBIC).

2. What are three possible ways of data transmission in CCNA?

• Simplex Mode: Simplex mode is sort of a unidirectional path within the communication is one-way. Only 1 of the 2 devices will send and the other will receive. 
• Half-Duplex Mode: Every station will broadcast and receive information in half-duplex mode, however, it is not at the identical time. once the device transmits data.
• Full-Duplex Mode:  Each station will broadcast and receive information at an identical time in full-duplex mode. Signals traveling in one direction share the link’s capability with signals traveling within the different directions in full-duplex mode:
  • Either the connection or the receiver must have two physically independent transmission routes.
  • On the other hand, capacitance is divided by signals moving in both directions.

For more details please refer to the Transmission Modes in Computer Networks (Simplex, Half-Duplex, and Full-Duplex) article.

3. Name different IPX access lists.

There are three IPX Access lists:

• Standard Access list: The access list is created using the source IP address. These ACLs allow or deny the whole protocol suite. They do not differentiate between the IP traffic such as TCP, UDP, HTTPS, etc. By using digits 1-99 or 1300-1999, the router will understand it as a standard ACL and set the address as the source IP address.
• Extended Access-list: It is a type of Access-list that is mainly used as it can differentiate IP traffic. the whole traffic will not be permitted or denied like in the standard access list. ACL uses both source and destination IP addresses and also port numbers to distinguish IP traffic. In this type of ACL, we can also mention which IP traffic should be allowed or denied. These use range of numbers 100-199 and 2000-2699.
• Reflexive Access list: Reflexive Access-list can be defined as an access list that allows only the responses of the packets on sessions created within the network from the outside network.

For more details please refer to the Access-Lists (ACL) article.

4. What do you mean by 100BaseFX?

100BASE-FX is another variation of the 100Base-T normal with the exception that it is a quick LAN i.e sending over fiber. Like various standards, 100Base uses two wires or in this case strings for data transmission: one for reception (RX), while the other for transmission (TX).

For more details please refer to the Fast Ethernet and Gigabit Ethernet article.

5. Name the LAN Switching method that is mostly used in CISCO Catalyst 5000?

The store-and-forward switching technique is used by the CISCO Catalyst 5000 and therefore it stores the entire frame in its buffers and performs a CRC (Cyclic Redundancy Check)  before deciding whether or not to transmit this information frame.

For more details please refer to the Message switching techniques article.

6. Name different memories that are used in CISCO routers.

The different memories that are used in Cisco routers are given below:

• Flash Memory 
• RAM ( Random Access Memory ) 
• ROM (Read Only Memory)
• NVRAM (Non-Volatile Random Access Memory)

For more details please refer to the different memories used in a CISCO router article.

7. What is the difference between tracert and traceroute?

Traceroute is a feature or a utility that records the route (explicit passage PCs at each bounce) through the organization between your PC and a predetermined objective PC and the Tracert tracking is a quick scan that shows a lot of tracking information of any network or device that can be obtained in a package from a PC or gadget.

For more details please refer to the Difference between Ping and Traceroute article

8. What do you mean by DLCI?

DLCI (Data Link Connection Identifier) is the quantity of a personal or switched virtual circuit in a frame relay network, situated within the frame header, the DLCI field identifies that logical circuit the data travels over, and each DLCI includes a committed information rate (CIR) associated with it.

For more details please refer to the Local Management Interface (LMI)

9. Name router command that is used to display RAM content and NVRAM Content.

To Show, the components of NVRAM or point to the arrangement file assigned to the CONFIG_FILE variable, we use the show startup-config command.

For more details please refer to the Cisco Router basic commands article.

10. Define Frame relay?

Frame relay is a technology that provides fast and reliable data transmission in Internet networks. It is a standards-based networking technology that provides a path for data packets from one point on the network to another.

For more details please refer to the How does Frame Relay Work article.

11. Difference between User mode and Privileged mode in Cisco? 

User mode is only for viewing router configurations and Privileged mode is for viewing all router configurations and also allows editing some less important configurations.

For more details please refer to the Cisco Router modes article.

12. What is EIGRP? Mention some metrics of the EIGRP Protocol.

EIGRP determines the path value from 5 metrics: bandwidth, load, delay, reliability, and MTU. EIGRP uses five different messages to communicate with neighboring routers. EIGRP Messages – Hello, Update, Question, Answer and Confirm.

For more details please refer to the EIGRP fundamentals article.

13 . What is CDP(Cisco Discovery Protocol)? Write its functions.

Cisco Discovery Protocol (CDP) is a network discovery tool that helps network administrators and technicians identify nearby Cisco devices, especially those with a low-transparency protocol.

For more details please refer to the Cisco Discovery Protocol (CDP) and Link Layer Discovery Protocol (LLDP) article.

14. Difference between a broadcast domain and a collision domain?

Both broadcast and collision domains overlap. Broadcast domain refers to the transmission of information over a wide area, such as television or radio broadcasting. The collision domain consists of two or more objects that come into contact with each other suddenly, violently, or unexpectedly.

For more details please refer to the Collision Domain and Broadcast Domain in the Computer Network article.

15. What do you mean by route poisoning?

Route poisoning is a way to control a router from transmitting packets through a path that has become weak within computer networks. Distance-vector routing protocols in computer networks use route poisoning to show other routers that a route is no longer reachable and should not be considered from their routing tables. The split horizon with poison reverses the route poisoning and delivers updates with unreachable hop counts directly to all the nodes in the network. When the protocol catches an invalid route, all of the routers in the network are notified that the bad route has an infinite (∞) route metric. This makes all nodes on the invalid route seem infinitely distant, stopping any of the routers from sending packets over the invalid path.

For more details please refer to the Route Poisoning article.

16. What types of passwords can be used in CISCO routers?

There are three types of passwords that can be used in a Cisco router. These are 

• Administrative passwords: They are used to control access to the router. They are used to assign permissions to users and to control the overall operation of the router. 
• User passwords: These are used to protect data stored on the router. They are used to log into the router and control access to the router.
• Password attributes: They are used to set a password limit, and to specify the amount of time that a password must be used before it is automatically changed.

For more details please refer to the Different Types of Passwords used in Securing Cisco Router article.

17. Write the difference between public IP and private IP.

A public IP address that identifies you on the Internet so that all the information you seek can find you. Private IP addresses are used within a private network to securely connect to other devices in the same network. Each device on the same network has a unique private IP address.

For more details please refer to the Private and Public IP article.

18. Explain PoE.

Power over Ethernet (PoE) is a measure that allows Ethernet cables to simultaneously transfer data and power using a single network cable. This permits system integration and network installers to establish powered appliances in areas that lack electrical circuitry. In addition, PoE stops the cost of installing extra electrical wiring, requiring professional electrical installers to assure that strict conduit regulations are followed. PoE technology transmits 10/100/1000 Mbps of data and 15W, 30W, 60W, and up to 90W of power budget to appliances over Cat5e, Cat6, and Cat6a. Cat7 and Cat8 Ethernet cables for the highest distance of 100m.

For more details please refer to the Power Over Ethernet (POE) article.

19. What is Round Trip Time?

RTT is also known as round-trip time is a crucial tool in defining the working condition of a network. It is the time between a request and the response in any kind of server on the internet. A round-trip time is measured in milliseconds. RTT can be examined and determined by pinging a specific address. It refers to the time taken by a network request to reach a final point and to revert back to the initial source.

For more details please refer to the RTT(Round Trip Time) article.

20. What is DHCP scope?

The DHCP scope is a valid range of IP addresses that are known for assignment or lease to client computers on an individual subnet. In a DHCP server, a scope is configured to determine the address pool of IPs that the server can provide to DHCP clients. DHCP Scopes define IP addresses that are provided to the clients. They should be determined and activated before DHCP clients use the DHCP server for its dynamic IP configuration. Users can configure as many scopes on a DHCP server as needed in the network environment.

For more details please refer to the Dynamic Host Configuration Protocol (DHCP) article.

21.  what is NVRAM?

NVRAM (Non-volatile random-access memory) is a computer memory that can keep data when power to the memory chips has been turned off. NVRAM is a part of the larger type of non-volatile memory (NVM), which contains storage-class memory based on NAND flash. Flash memory chips are slow to read to and write than RAM chips, making them less well fitted for active computational memory.

22. What is the use of “Service Password Encryption”?

Service Password Encryption  Command on CISCO Router/Switch  Permits you to encrypt all passwords on your router so that they cannot be easily assumed from your running configuration. This command uses very weak encryption because the router has to decrypt the password very quickly for it to work.

For more details please refer to the Different Types of Passwords used in Securing Cisco Router article.

23.  Explain different cable types?

There are commonly two types of cables used in networking, described below.

• Coaxial cable: A coaxial cable is a kind of copper cable specially made with a metal guard and other parts arranged to stop signal interference. It is mainly used by cable TV firms to connect their satellite antenna installations to customers’ homes and businesses. It is also sometimes used by telephone companies to secure central offices to telephone poles near customers. Some homes and offices use coaxial cable, too, but its general use as an Ethernet connectivity medium in companies and data centers has been replaced by the deployment of twisted pair cabling.
• Twisted pair: Twisted pair Ethernet is an Ethernet in a computer network that uses twisted pairs of insulated copper wires for the physical layer of the network, which is connected to the data link layer. Twisted pair cable wires are turned around each other to reduce obstacles from other twisted pairs in the cable. The two twisted wires help in reducing crosstalk that can disrupt signals and decrease electromagnetic induction, which has a voltage across a conductor moving through a magnetic field. 

For more details please refer to the Types of Ethernet Cable article.

24.  What is the port number of DNS and Telnet?

The Port number of Telnet is 23 and the Port number of DNS is 53..

For more details please refer to the Various TCP and UDP ports article.

25. Which service uses both TCP and UDP?

The Domain Name System (DNS) uses the TCP and UDP protocols for communication.UDP is used for lower communications and is ideal for DNS queries.TCP is used for zone transfers and is suitable for large response messages.

For more details please refer to the Various TCP and UDP ports article.

26. What is the port number of SMTP and POP3?

The Port number of SMTP is 587 and the Port number of POP3 is 110.

For more details please refer to the Difference between SMTP and POP3 article.

27. What is CRC? Which layer does CRC work on?

CRC stands for Cyclic Redundancy Check. It is a checksum algorithm used to detect errors in digital data streams transmitted between two or more computers. The layer where CRC works depends on the type of data being checked and how it needs to be processed by the system. In most cases, CRC is applied at the lower layer of an OSI model stack (OSI Reference Model).

For more details please refer to the Cyclic Redundancy Check article.

28. Which one is reliable – TCP or UDP ? and why?

TCP is reliable because it guarantees the delivery of data to the destination router. The delivery of data to the destination can not be secured in UDP.

For more details please refer to the Various TCP and UDP ports article.

29. What is the port number of FTP (data) and FTP?

The Port number of FTP (data) is 20 and the Port number of FTP is 21. 

For more details please refer to the File Transfer Protocol (FTP) article.

30.  Which layer provides the logical addressing that routers will use for path determination?

The Network layer provides logical addressing, typically IP addressing and routing.

For more details please refer to the Network Layer Services- Packetizing, Routing, and Forwarding article.

31. DNS uses which protocol? Why?

The Domain Name System (DNS) uses Transmission Control Protocol (TCP) for zone transfers and User Datagram Protocol (UDP) for name queries.UDP exchanges fewer data than TCP.

For more details please refer to the  Why does DNS use UDP and not TCP article.

32. Differentiate between forwarding lookup and reverse lookup in DNS?

Forward DNS and reverse DNS lookups are two different methods of accessing the Internet. The forward area is the DNS zone where the hostname is stored in the IP address relationship. Reverse DNS is the query method for determining the domain name associated with an IP address.

For more details please refer to the How to Implement Reverse DNS Look Up Cache? article.

33. What is Split Horizon Cisco?

A split horizon is developed to stop routing loops. Routing loops happen when a loop is created between two or more routers. For example, Router 1 has a network path to 192.168.1.0 via Router 2. Router 2 has a path to the same network, but it is back via Router 1. Therefore, Router 1 sends packets for 192.168.1.0 to Router 2, which then transmits the packets back to Router 1. This looping continues until the TTL (Time to Live) on the packet expires.

For more details please refer to the  Route Poisoning and Count to infinity problem in the Routing article.

34. Why is RIP known as Distance Vector?

The Routing Information Protocol (RIP) is the oldest distance-vector routing protocol that uses the hop count as a routing metric. RIP stops routing loops by executing a limit on the number of hops authorized in a path from source to destination. The largest number of hops allowed for RIP is 15, which limits the size of networks that RIP can support. RIP executes the split horizon, route poisoning, and hold-down means to prevent the wrong routing information from being propagated. In RIPv1 routers broadcast updates with their routing table every 30 seconds. In the early deployments, routing tables were short enough that the traffic was not important. As networks grew in size, however, it became obvious there could be a huge traffic burst every 30 seconds, even if the routers had been initialized at random times. 

For more details please refer to the Routing Information Protocol (RIP) article.

35. What is the administrative distance of RIP?

By default, OSPF has a default management level of 110 and RIP has a default management level of 120.

For more details please refer to the Routing Information Protocol (RIP) article.

36. What is the limit of hop count in RIP?

The limit of hop count in RIP is 15. Networks with a hop count of 16 or more are unreachable.

For more details please refer to the Routing Information Protocol (RIP) article.

37. How is RIP select the best path to the remote network?

The main function of the router is to determine the best way to send the packets. To determine the best route, a router searches its router table to find a network address similar to the destination IP address of the package.

For more details please refer to the Routing Information Protocol (RIP) article.

38. What are the differences between RIPv1 and RIPv2?

RIPv1 uses a standard route. Occasional updates do not have subnet information and no support for VLSM. This limitation makes it impossible to have subnets of different sizes within the same network category. In other words, all subnets in the network class should be the same size. There is also no router authentication support, which makes RIP vulnerable to various attacks. RIPv2 is a vector distance route protocol defined in RFC 1723. As a phaseless protocol, it means, it included a subnet mask and network addresses in its router updates.

For more details please refer to the Differences between RIPv1 and RIPv2 article.

39. What is pinhole congestion?

In computer networking, the router makes decisions regarding the way a packet will travel, based on the number of hops it carries to reach the destination and if it had 2 other ways to get there, it will only send it via the shortest path, regardless of the connection speed. This is known as pinhole congestion.

For more details please refer to the Congestion Control in Computer Networks article.

40. What is a passive interface in RIP?

Router (config-router) # passive-interface serial0 / 0/0. Sets the interface as idle, meaning that route updates will not be sent to this interface. NOTE: In RIP, the passive-interface command will prevent the inter-face from sending route updates but will allow the visual interface to receive updates.

For more details please refer to the Passive-Interface Command Behavior in RIP, EIGRP & OSPF article.

41. Explain the loop avoidance mechanism in RIP.

The following methods are used to avoid Routing Loops in RIP:

• The maximum hop count mechanism can be used to block Routing Loops. Vector distance protocols use the TTL (Lifetime) value in the IP data header to avoid loops.
• Split horizontal is the setting of the route that stops the route from being advertised back to where it came from.
• Route Poisoning is another way to avoid loops. If the router finds that one of its connected routes has failed, the router will be toxic to the route by providing endless metrics to it.

For more details please refer to the  Routing Loop and How to Avoid Routing Loop article.

42. Why EIGRP is called hybrid protocol?

EIGRP does not transfer all data to the Routing table when changes are made, but will only transfer changes made since the Routing table was last updated. EIGRP does not send its routing table periodically, but will only send routing data in the event of a real change. This behavior is highly compliant with link-state routing regulations, so EIGRP is considered a hybrid protocol.

For more details please refer to the EIGRP fundamentals article.

43.  What is meant by active and passive states in EIGRP?

• Active State: Routes where a follower route fails and no follower routes are likely to move to a functional state forcing EIGRP to submit query packages and reconnect. 
• Passive State: The route is in a passive state where the route has a route to follow, and no failures have occurred so far.

For more details please refer to the EIGRP fundamentals article.

44. What does stuck-in-active mean?

EIGRP is a reliable protocol and for each question the route you send to its neighbors you must get a response within 3 minutes. If the router does not get an answer to ALL its pending questions it will set the stage for SIA (STUCK INACTIVE) and kill the nearest neighbor.

45.  What is the EIGRP Feasibility Condition?

The Feasibility condition states that the route will not be accepted if the Reported Range exceeds the best possible Route range. Or it means another way from a router’s point of view: the path to the network will not be accepted if my neighbor’s cost exceeds my cost. 

For more details please refer to the EIGRP Cost Calculation article.

46. Explain what will happen if the packet is not acknowledged?

If a packet is not acknowledged by the network, it means that the data was successfully delivered to its destination but no response was received from either end. As long as both ends are aware of each other and have been configured correctly, there should be no reason for the receiving node to do anything further with this packet. Data may still be flowing through this connection because acknowledgments take the time or because some intermediate nodes might be buffering packets before forwarding them on. However, if at any point in time you notice your traffic slowing down noticeably or becoming completely unavailable due to an excessive number of lost packets (especially during high-traffic times), then it’s likely that something has gone wrong and you’ll need to investigate what caused it.

For more details please refer to the Stop and Wait for protocol, and its problems, and solutions article.

47. Explain Null Zero in EIGRP?

It is a visual interface used to ensure that routes enter the RIB, the tracks must have the next-hop to get into the RIB. If a packet arrives on a device with a route to Null 0 and is not elsewhere, it will dispose of it as the ACL would. Think of it as a visible interaction when the packets die well.

For more details please refer to the article EIGRP fundamentals 

48.  What is the EIGRP stub routing feature?

The EIGRP stub routing feature allows the network administrator to prevent queries from being sent to a remote device. In addition to a simple hub and spoke network, where the remote device is connected to a single distribution device, the remote device can have a dual home on two or more distribution devices.

49. Difference between LSA & LSU in OSPF?

Link State Update (LSU) packs are OSPF Type 4. packs. Each LSA contains route, metrics, and topology information to define part of the OSPF network. The local router advertises the LSA inside the LSU package to its neighbors.

50.  What is Route Redistribution in computer networks?

The use of a routing protocol to broadcast routes that are known by some other means, such as by another routing protocol, static routes, or directly connected routes, is called redistribution. While operating a single routing protocol throughout your whole IP internetwork is desirable, multi-protocol routing is common for a number of reasons, such as enterprise unions, multiple departments controlled by multiple network administrators, and multi-vendor environments. Running other routing protocols is usually part of a network design. In any case, having a multiple protocol environment makes redistribution a need.