CCNA Interview Questions and Answers for freshers

1. What is the difference between a router and a switch?

   • Answer: A router operates at the Network Layer (Layer 3) of the OSI model and forwards data packets between networks based on their IP addresses. A switch operates at the Data Link Layer (Layer 2) and forwards data frames within a single network based on MAC addresses. Routers connect different networks, while switches connect devices within the same network.

2. Explain the OSI model.

   • Answer: The OSI model is a conceptual framework that standardizes the functions of a telecommunication or computing system without regard to its underlying internal structure and technology. It consists of seven layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application. Each layer has specific functions and interacts with the layers above and below it.

3. What is subnetting?

   • Answer: Subnetting is the process of dividing a large network into smaller, logical subnetworks. This improves network efficiency, security, and scalability by organizing devices and controlling broadcast domains.

4. Explain the difference between IPv4 and IPv6.

   • Answer: IPv4 uses 32-bit addresses, resulting in a limited number of available addresses. IPv6 uses 128-bit addresses, providing a vastly larger address space. IPv6 also offers improved security features and simplified header structure.

5. What is a MAC address?

   • Answer: A MAC (Media Access Control) address is a unique physical address assigned to a network interface card (NIC). It's used by switches to forward data frames within a local network.

6. What is DHCP?

   • Answer: DHCP (Dynamic Host Configuration Protocol) is a network management protocol used to automatically assign IP addresses and other network configuration parameters to devices on a network.

7. What is a default gateway?

   • Answer: The default gateway is the IP address of the router that a device uses to send data packets to networks outside its own subnet.

8. What is a subnet mask?

   • Answer: A subnet mask is a 32-bit number used to identify the network portion and the host portion of an IP address. It determines which part of the IP address belongs to the network and which part belongs to the specific device on that network.

9. What is the difference between static and dynamic routing?

   • Answer: Static routing involves manually configuring routes on a router. Dynamic routing uses routing protocols (like RIP, OSPF, EIGRP) to automatically discover and update routes.

10. Explain RIP routing protocol.

    • Answer: RIP (Routing Information Protocol) is a distance-vector routing protocol that uses hop count as a metric. It's simple to configure but has limitations in terms of scalability and convergence speed.

11. Explain OSPF routing protocol.

    • Answer: OSPF (Open Shortest Path First) is a link-state routing protocol that uses cost as a metric. It's more scalable and efficient than RIP, offering faster convergence.

12. What is VLSM?

    • Answer: VLSM (Variable Length Subnet Masking) is a subnetting technique that allows using different subnet masks for different subnetworks, optimizing IP address utilization.

13. What is NAT?

    • Answer: NAT (Network Address Translation) is a method used to translate private IP addresses to public IP addresses and vice versa. It conserves public IP addresses and enhances network security.

14. What is ACL?

    • Answer: ACL (Access Control List) is a set of rules used to control network access based on source and destination IP addresses, ports, and other criteria. They are used to filter traffic and enhance network security.

15. Explain the concept of a VLAN.

    • Answer: A VLAN (Virtual Local Area Network) is a logical grouping of devices on a network that act as if they are on the same physical LAN, even if they are geographically separated. It allows for better network segmentation and security.

16. What is STP?

    • Answer: STP (Spanning Tree Protocol) is a network protocol that prevents loops in a switched network. It ensures that only one active path exists between any two network devices, avoiding broadcast storms.

17. What is RSTP?

    • Answer: RSTP (Rapid Spanning Tree Protocol) is an improved version of STP that provides faster convergence in the event of network topology changes.

18. What is MSTP?

    • Answer: MSTP (Multiple Spanning Tree Protocol) is a more sophisticated spanning tree protocol that allows for the creation of multiple spanning trees within a network, enhancing scalability and flexibility.

19. What is a Frame Relay?

    • Answer: Frame Relay is a WAN technology that uses packets to transfer data between networks. It's a connection-oriented protocol providing efficient data transmission over a wide area network.

20. What is PPP?

    • Answer: PPP (Point-to-Point Protocol) is a data link layer protocol used to establish a connection between two nodes over a point-to-point link. It is commonly used for dial-up connections and other point-to-point links.

21. What is HDLC?

    • Answer: HDLC (High-Level Data Link Control) is a bit-oriented synchronous data link layer protocol used for point-to-point and multipoint communication links.

22. What is EIGRP?

    • Answer: EIGRP (Enhanced Interior Gateway Routing Protocol) is a Cisco proprietary distance-vector routing protocol that combines features of both distance-vector and link-state routing protocols. It's known for its fast convergence and scalability.

23. What is BGP?

    • Answer: BGP (Border Gateway Protocol) is an exterior gateway protocol used to exchange routing information between autonomous systems (AS) on the Internet. It's used for routing between different networks.

24. What is a loopback interface?

    • Answer: A loopback interface is a virtual interface that allows a router or computer to send and receive data to itself. It's commonly used for testing and configuration.

25. What is a wildcard mask?

    • Answer: A wildcard mask is used in conjunction with an access control list (ACL) to specify which bits of an IP address should be matched. It's the inverse of the subnet mask.

26. What are the different types of cables used in networking?

    • Answer: Common types include coaxial cable, twisted-pair cable (shielded and unshielded), and fiber optic cable. Each has different characteristics in terms of speed, distance, and cost.

27. What is the difference between a straight-through and a crossover cable?

    • Answer: A straight-through cable connects devices of different types (e.g., computer to router). A crossover cable connects devices of the same type (e.g., computer to computer), though this is less common now with auto-MDIX switches.

28. What is a router configuration register?

    • Answer: The configuration register controls the boot process of a Cisco router. It specifies where the router should load its configuration from (flash memory, TFTP server, etc.).

29. Explain the concept of bandwidth.

    • Answer: Bandwidth refers to the transmission capacity of a network or communication channel. It's typically measured in bits per second (bps).

30. What is latency?

    • Answer: Latency is the delay in transmitting data over a network. It's the time it takes for a packet to travel from source to destination.

31. What is jitter?

    • Answer: Jitter is the variation in latency over time. Unpredictable jitter can negatively impact real-time applications like VoIP.

32. What is a network topology?

    • Answer: Network topology refers to the physical or logical layout of a network. Common topologies include bus, star, ring, mesh, and tree.

33. What is a physical topology?

    • Answer: The physical topology refers to the actual arrangement of cables and devices in a network.

34. What is a logical topology?

    • Answer: The logical topology describes how data flows through the network, independent of the physical layout.

35. What is a broadcast domain?

    • Answer: A broadcast domain is a portion of a network where devices can communicate with each other using broadcast messages.

36. What is a collision domain?

    • Answer: A collision domain is a segment of a network where data collisions can occur. Switches reduce the size of collision domains.

37. What is a routing table?

    • Answer: A routing table is a database that a router uses to determine the best path to forward data packets to their destination networks.

38. What is the command to display the routing table on a Cisco router?

    • Answer: `show ip route`

39. What is the command to ping a remote host?

    • Answer: `ping [IP address]`

40. What is the command to trace the route to a remote host?

    • Answer: `traceroute [IP address]` or `tracert [IP address]` (on Windows)

41. What is the command to display the MAC address table on a Cisco switch?

    • Answer: `show mac address-table`

42. What is the command to show the interfaces on a Cisco router or switch?

    • Answer: `show interfaces`

43. What is Telnet?

    • Answer: Telnet is a network protocol used to access remote devices. However, it's insecure because it transmits data in plain text. SSH is preferred for secure remote access.

44. What is SSH?

    • Answer: SSH (Secure Shell) is a secure network protocol used to access remote devices. It encrypts data transmission, providing secure remote access.

45. What is TFTP?

    • Answer: TFTP (Trivial File Transfer Protocol) is a simple network protocol used to transfer files between a client and a server. It's often used for downloading router configuration files.

46. What is FTP?

    • Answer: FTP (File Transfer Protocol) is a network protocol used to transfer files between a client and a server. It offers more features than TFTP, but can be less secure unless using SSL/TLS.

47. What is HTTP?

    • Answer: HTTP (Hypertext Transfer Protocol) is the foundation of data communication for the World Wide Web. It's used to transfer web pages and other web resources.

48. What is HTTPS?

    • Answer: HTTPS (Hypertext Transfer Protocol Secure) is an extension of HTTP that uses SSL/TLS to encrypt communication, providing secure web browsing.

49. What is DNS?

    • Answer: DNS (Domain Name System) is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network.

50. What is a DNS server?

    • Answer: A DNS server is a computer that stores and manages domain name records, translating domain names into IP addresses and vice versa.

51. What is SNMP?

    • Answer: SNMP (Simple Network Management Protocol) is a network protocol used to monitor and manage network devices. It allows administrators to collect performance data and configure devices remotely.

52. What is an SNMP agent?

    • Answer: An SNMP agent is a software application that runs on a network device and provides information to an SNMP manager.

53. What is an SNMP manager?

    • Answer: An SNMP manager is a software application that collects and analyzes information from SNMP agents.

54. What is a port?

    • Answer: A port is a logical address used by applications to communicate over a network. It's a number between 0 and 65535.

55. What is a well-known port?

    • Answer: A well-known port is a port number below 1024 that's assigned to a specific application or service (e.g., port 80 for HTTP, port 21 for FTP).

56. What is TCP/IP?

    • Answer: TCP/IP is the suite of communication protocols used to connect devices to the Internet. It encompasses several protocols, including TCP, UDP, IP, etc.

57. What is TCP?

    • Answer: TCP (Transmission Control Protocol) is a connection-oriented protocol that provides reliable data transmission. It guarantees delivery of data packets in the correct order and without errors.

58. What is UDP?

    • Answer: UDP (User Datagram Protocol) is a connectionless protocol that provides unreliable data transmission. It's faster than TCP but doesn't guarantee delivery or order of packets.

59. What is IP?

    • Answer: IP (Internet Protocol) is a connectionless protocol responsible for addressing and routing data packets across networks.

60. What is ICMP?

    • Answer: ICMP (Internet Control Message Protocol) is used for error reporting and network diagnostics. `ping` uses ICMP.

61. What is a routing protocol?

    • Answer: A routing protocol is a set of rules and procedures used by routers to exchange routing information and determine the best path for data packets.

62. What is a metric in routing?

    • Answer: A metric is a value used by routing protocols to evaluate the cost or desirability of a particular route. Examples include hop count, bandwidth, and delay.

63. What is convergence in routing?

    • Answer: Convergence is the process by which routers in a network reach a stable routing state after a topology change.

64. What is a routing loop?

    • Answer: A routing loop occurs when a data packet is endlessly forwarded between routers without ever reaching its destination.

65. How can routing loops be prevented?

    • Answer: Using protocols like STP to prevent loops in the LAN and employing proper routing protocols with mechanisms to avoid loops (like split horizon).

66. What is a hierarchical routing design?

    • Answer: A hierarchical routing design organizes a network into areas or regions, reducing the complexity of routing and improving scalability. It uses different routing protocols for different levels (e.g., OSPF within areas, BGP between areas).

67. What is the difference between Layer 2 and Layer 3 devices?

    • Answer: Layer 2 devices (switches) operate at the data link layer using MAC addresses, while Layer 3 devices (routers) operate at the network layer using IP addresses. Layer 3 devices route traffic between different networks.

68. What is the command to configure a basic IP address on a Cisco interface?

    • Answer: `ip address `

69. What is the command to enable an interface on a Cisco device?

    • Answer: `no shutdown`

70. What is the command to disable an interface on a Cisco device?

    • Answer: `shutdown`

71. What is the command to save the configuration on a Cisco device?

    • Answer: `copy running-config startup-config`

72. What is the importance of network security?

    • Answer: Network security is crucial to protect sensitive data from unauthorized access, prevent cyberattacks, and maintain network availability and reliability.

73. What are some common network security threats?

    • Answer: Common threats include malware, phishing attacks, denial-of-service (DoS) attacks, man-in-the-middle attacks, and unauthorized access.

74. What are some ways to improve network security?

    • Answer: Implementing firewalls, intrusion detection/prevention systems (IDS/IPS), access control lists (ACLs), virtual private networks (VPNs), and regular security updates are key.

75. What is a firewall?

    • Answer: A firewall is a network security system that monitors and controls incoming and outgoing network traffic based on predefined security rules.

76. What is an IDS?

    • Answer: An IDS (Intrusion Detection System) is a system that monitors network traffic for malicious activity and alerts administrators to potential threats.

77. What is an IPS?

    • Answer: An IPS (Intrusion Prevention System) is similar to an IDS, but it also takes action to block or mitigate threats.

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