Most Asked CCNA Interview Questions [2025 Updated]

Network Architecture Basics

1. What is a network topology, and what are common types?

A network topology defines how devices are connected. Common types:

• Star: Central hub/switch, easy to manage, used in LANs.
• Bus: Single backbone, prone to collisions, outdated.
• Ring: Devices form a loop, used in token ring networks.
• Mesh: Multiple connections, high redundancy, used in WANs.
  Each impacts scalability and reliability.

2. What is the purpose of a layered network model?

Layered models (e.g., OSI, TCP/IP) separate network functions for modularity, simplifying design, interoperability, and troubleshooting by isolating issues to specific layers.

3. What is a packet, and how does it differ from a frame?

A packet is a Layer 3 data unit with IP headers, used for routing. A frame is a Layer 2 unit with MAC headers, used for local delivery. Packets are encapsulated in frames.

4. What is bandwidth, and why does it matter?

Bandwidth is the maximum data transfer rate (e.g., Mbps). It determines network performance, affecting application speed and user experience.

5. What is latency, and how does it impact networks?

Latency is the delay in data transmission. High latency slows real-time apps like VoIP, caused by distance, congestion, or processing delays.

6. What is a collision in networking?

A collision occurs when multiple devices transmit simultaneously on a shared medium (e.g., hub-based LAN), causing data loss. Switches eliminate collisions.

7. What is the role of a gateway?

A gateway connects different networks (e.g., LAN to WAN), translating protocols or addressing schemes, unlike routers which route within similar protocols.

8. What is a broadcast storm?

A broadcast storm floods a network with excessive broadcast packets, often due to loops, overwhelming devices and degrading performance.

9. What is the difference between half-duplex and full-duplex?

• Half-Duplex: One-way communication at a time (e.g., walkie-talkie).
• Full-Duplex: Simultaneous two-way communication (e.g., modern switches).

10. What is a network segment?

A portion of a network separated by switches, routers, or VLANs, reducing congestion and improving performance.

Routing Protocols and Concepts

11. What is a routing protocol, and why is it needed?

A routing protocol determines the best path for data between networks (e.g., RIP, OSPF). It enables dynamic route updates, ensuring efficient traffic flow.

12. What is a metric in routing?

A metric (e.g., hop count, bandwidth) measures path efficiency, used by protocols to select optimal routes. Lower metrics are preferred.

13. What is convergence in routing?

Convergence is when all routers update their routing tables after a network change, ensuring consistent paths. Faster convergence improves reliability.

14. What is a loopback interface?

A virtual interface (e.g., Loopback0) on a router, always up, used for testing, management, or as a stable router ID in protocols.

15. What is the difference between intra-VLAN and inter-VLAN routing?

• Intra-VLAN: Routing within a VLAN, handled by switches.
• Inter-VLAN: Routing between VLANs, requiring a Layer 3 device (e.g., router-on-a-stick).

16. What is a next-hop address?

The IP address of the next router in a packet’s path, used in routing tables to forward traffic.

17. What is path vector routing?

Tracks the path (sequence of autonomous systems) to a destination, used by BGP to prevent loops and select routes.

18. What is a routing loop, and how is it prevented?

A routing loop occurs when packets cycle between routers. Prevented by protocols like BGP (path vector) or TTL decrements.

19. What is the role of a designated router in OSPF?

Reduces update traffic by managing link-state advertisements in multi-access networks, elected by priority or router ID.

20. What is a backup designated router (BDR)?

A standby router in OSPF that takes over if the designated router fails, ensuring continuity.

Switching and VLANs

21. What is a switch’s forwarding decision based on?

Switches forward frames based on destination MAC addresses, using a MAC address table built via source address learning.

22. What is VLAN tagging, and why is it used?

VLAN tagging (e.g., 802.1Q) adds identifiers to frames to distinguish VLANs on trunk links, enabling multi-VLAN traffic.

23. What is the difference between a managed and unmanaged switch?

• Managed: Configurable (VLANs, QoS), used in enterprises.
• Unmanaged: Plug-and-play, no configuration, for small networks.

24. What is a native VLAN?

The default VLAN for untagged frames on a trunk port, typically VLAN 1 unless configured otherwise.

25. What is the purpose of a switchport mode?

Defines port behavior:

• Access: Single VLAN for end devices.
• Trunk: Multiple VLANs for inter-switch links.

26. What is a MAC address table overflow attack?

Floods a switch with fake MAC addresses, filling the table and forcing flooding, allowing attackers to capture traffic.

27. What is the role of a root port in STP?

The port on a non-root switch with the lowest path cost to the root bridge, used for forwarding in STP.

28. What is a blocked port in STP?

A port disabled by STP to prevent loops, placed in a blocking state to avoid redundant paths.

29. What is the benefit of link aggregation?

Combines multiple links (e.g., via LACP) for higher bandwidth and failover redundancy.

30. What is a switch virtual interface (SVI)?

A virtual Layer 3 interface on a switch (e.g., VLAN 10 interface) for inter-VLAN routing or management.

IP Addressing and Services

31. What is a default subnet mask?

The standard mask for IP classes:

• Class A: 255.0.0.0 (/8).
• Class B: 255.255.0.0 (/16).
• Class C: 255.255.255.0 (/24).

32. What is VLSM, and why is it useful?

Variable Length Subnet Masking (VLSM) allows different subnet mask sizes, optimizing IP address allocation for varied host needs.

33. What is a directed broadcast?

A packet sent to a subnet’s broadcast address (e.g., 192.168.1.255), reaching all hosts in that subnet.

34. What is the purpose of a proxy ARP?

A router responds to ARP requests on behalf of another device, enabling communication across subnets without changing configurations.

35. What is a DHCP relay agent?

Forwards DHCP requests to a server in another subnet, enabling centralized IP management.

36. What is the difference between a static and dynamic IP?

• Static: Manually assigned, fixed.
• Dynamic: Auto-assigned by DHCP, temporary.

37. What is a multicast address?

Sends packets to a group of devices (e.g., 224.0.0.0–239.255.255.255 for IPv4), used for streaming or routing updates.

38. What is the role of a DNS resolver?

Queries DNS servers to resolve domain names to IP addresses for client devices.

39. What is a private VLAN?

Isolates devices within a VLAN for enhanced security (e.g., isolating guest devices).

40. What is the purpose of a time-to-live (TTL) field?

Limits packet lifespan by decrementing per hop, preventing infinite loops.

Network Security Essentials

41. What is a MAC filter?

Restricts network access to specific MAC addresses, enhancing switch security.

42. What is the difference between authentication and authorization?

• Authentication: Verifies identity (e.g., username/password).
• Authorization: Defines permissions (e.g., access levels).

43. What is a VLAN access map?

Filters traffic between VLANs, similar to ACLs, for granular security control.

44. What is a man-in-the-middle attack?

An attacker intercepts communication between devices to steal data or manipulate traffic.

45. What is the purpose of SSH in networking?

Provides secure remote access to devices, encrypting traffic unlike Telnet.

46. What is a security zone?

Groups interfaces for firewall policies, controlling traffic flow (e.g., inside, outside zones).

47. What is a denial-of-service (DoS) attack?

Overwhelms a network or device to disrupt availability, mitigated by rate limiting or firewalls.

48. What is the role of a digital certificate?

Verifies identity in secure communications (e.g., SSL), ensuring trust and encryption.

49. What is DHCP snooping?

Prevents rogue DHCP servers by filtering untrusted DHCP messages, ensuring IP integrity.

50. What is a VLAN hopping attack?

Exploits misconfigured trunks to access other VLANs, mitigated by disabling auto-negotiation.

Wireless and Mobility

51. What is a wireless LAN controller (WLC)?

Manages multiple access points for centralized configuration, security, and roaming.

52. What is the purpose of a service set?

Defines a Wi-Fi network, including BSS (single AP) or ESS (multiple APs with same SSID).

53. What is Wi-Fi channel bonding?

Combines adjacent channels (e.g., 40 MHz in 5 GHz) to increase bandwidth and throughput.

54. What is a rogue access point?

An unauthorized AP that risks security, detected via WLC or monitoring tools.

55. What is the difference between open and secure Wi-Fi authentication?

• Open: No password, insecure.
• Secure: Uses WPA2/WPA3 with passwords or 802.1X for authentication.

56. What is a wireless bridge?

Connects two wired networks wirelessly, extending LANs without cables.

57. What is the role of RF interference in Wi-Fi?

Disrupts signals (e.g., from microwaves), reducing performance; mitigated by channel selection.

58. What is fast roaming in Wi-Fi?

Enables seamless AP handoffs for mobile devices, critical for VoIP or video.

59. What is the difference between 802.11ac and 802.11ax?

• 802.11ac: 5 GHz, high speed (Wi-Fi 5).
• 802.11ax: 2.4/5 GHz, better efficiency, supports IoT (Wi-Fi 6).

60. What is a wireless site survey?

Analyzes RF coverage to optimize AP placement and performance.

WAN and Connectivity

61. What is a wide area network (WAN)?

Connects geographically distant networks (e.g., branch offices) via leased lines or VPNs.

62. What is a virtual circuit in WANs?

A logical path (e.g., in Frame Relay) for data between endpoints, ensuring reliable delivery.

63. What is the difference between MPLS and SD-WAN?

• MPLS: Uses labels for reliable, private WAN routing.
• SD-WAN: Leverages internet for cost-effective, software-driven connectivity.

64. What is a site-to-site VPN?

Connects entire networks (e.g., branch to HQ) over encrypted tunnels, using IPsec.

65. What is the purpose of QoS in WANs?

Prioritizes critical traffic (e.g., VoIP) to ensure performance over limited bandwidth.

66. What is a leased line?

A dedicated physical connection for reliable, high-speed WAN connectivity.

67. What is the role of a tunnel interface?

Creates virtual links (e.g., GRE) to encapsulate and route traffic across networks.

68. What is a Frame Relay DLCI?

Data Link Connection Identifier assigns virtual circuits in Frame Relay for WAN routing.

69. What is the difference between circuit-switched and packet-switched WANs?

• Circuit-Switched: Dedicated path (e.g., ISDN).
• Packet-Switched: Shared paths (e.g., MPLS, internet).

70. What is a DMZ in networking?

A demilitarized zone isolates public-facing servers (e.g., web servers) for security.

Network Monitoring and Management

71. What is the purpose of a network baseline?

Establishes normal performance metrics for comparison during troubleshooting.

72. What is a syslog server?

Centralizes device logs for monitoring and analysis, aiding issue diagnosis.

73. What is the role of SNMP traps?

Alerts sent from devices to managers about events (e.g., interface down), enabling proactive monitoring.

74. What is a network management protocol?

Enables device monitoring/control (e.g., SNMP, NETCONF) for efficient management.

75. What is the difference between in-band and out-of-band management?

• In-Band: Via production network (e.g., SSH).
• Out-of-Band: Via separate network (e.g., console), for reliability.

76. What is a network performance metric?

Measures like throughput, latency, or jitter, used to assess network health.

77. What is the purpose of a configuration backup?

Saves device settings to restore after failures or misconfigurations.

78. What is a network audit?

Reviews configurations, security, and performance to ensure compliance and efficiency.

79. What is the role of a network analyzer?

Captures and analyzes packets (e.g., via Wireshark) for troubleshooting and security.

80. What is a keepalive packet?

Tests connectivity between devices, ensuring links remain active.

Automation and Programmability

81. What is network automation, and why is it important in 2025?

Automates repetitive tasks (e.g., configuration) using tools like Ansible, reducing errors and scaling for IoT/cloud.

82. What is a REST API in networking?

Enables device configuration/monitoring via HTTP requests, supporting automation.

83. What is the role of Python in network automation?

Scripts tasks like configuration or monitoring, integrating with APIs for efficiency.

84. What is a YANG model?

A data modeling language for NETCONF, defining device configuration structures.

85. What is the difference between configuration management and orchestration?

• Configuration Management: Sets device parameters (e.g., Ansible).
• Orchestration: Coordinates multiple systems for workflows (e.g., Cisco DNA).

86. What is a controller-based network?

Uses centralized controllers (e.g., SDN) for dynamic configuration and management.

87. What is the benefit of zero-touch provisioning?

Automatically configures new devices without manual setup, speeding deployments.

88. What is a network programmability tool?

Software like Ansible or Python scripts for automating network tasks.

Emerging Networking Trends

89. What is network function virtualization (NFV)?

Virtualizes network services (e.g., firewalls) on commodity hardware, reducing costs.

90. What is the role of cloud networking in 2025?

Integrates on-premises networks with cloud platforms (e.g., AWS) for scalability and flexibility.

91. What is intent-based networking (IBN)?

Automates network configurations based on business goals, improving efficiency.

92. What is the impact of IoT on networking?

Drives demand for IPv6, low-latency protocols, and robust security for connected devices.

93. What is network slicing?

Creates virtual networks on shared infrastructure (e.g., 5G) for tailored performance.

94. What is the role of AI in networking?

Optimizes traffic, predicts failures, and automates tasks for smarter networks.

95. What is edge computing in networking?

Processes data closer to devices (e.g., IoT) for low latency and efficiency.

96. What is the benefit of IPv6 in modern networks?

Provides vast addresses, simplifies routing, and supports IoT/5G without NAT.

97. What is a software-defined perimeter (SDP)?

Secures access by verifying users/devices before granting connectivity, enhancing zero-trust.

98. What is Wi-Fi 6E?

Extends Wi-Fi 6 to 6 GHz band for higher capacity and less interference.

99. What is the role of 5G in enterprise networking?

Enables high-speed, low-latency connections for IoT, AR, and mobile workforces.

100. What is a zero-trust security model?

Requires continuous verification of all devices/users, critical for 2025 cybersecurity.

101. What are essential CCNA skills for 2025?

• VLAN and routing protocol configuration.
• IPv6 implementation.
• Automation with Python/Ansible.
• Security (ACLs, VPNs).
• Cloud and SDN knowledge.

Tips for Acing Your CCNA Interview

• Practice hands-on with tools like Packet Tracer.
• Master key commands and their outputs.
• Stay updated on IPv6, automation, and cloud trends.
• Explain technical concepts simply and confidently.
• Use Cisco’s official guides and lab practice for prep.