150+ CCNA Interview Questions and Answers [Networking Basics – 2025]

Networking Fundamentals

1. What is the OSI model, and what are its seven layers?

The OSI (Open Systems Interconnection) model is a conceptual framework that standardizes network functions into seven layers:

• Physical Layer: Transmits raw bits over cables or wireless media (e.g., Ethernet cables, hubs).
• Data Link Layer: Ensures error-free data transfer using MAC addresses (e.g., switches, Ethernet).
• Network Layer: Manages logical addressing and routing (e.g., IP, routers).
• Transport Layer: Provides reliable data transfer with flow control (e.g., TCP, UDP).
• Session Layer: Establishes and manages sessions between applications.
• Presentation Layer: Translates data, handling encryption and compression.
• Application Layer: Supports end-user applications (e.g., HTTP, DNS).
  This model simplifies network design and troubleshooting.

2. How does the TCP/IP model differ from the OSI model?

The TCP/IP model is a four-layer, practical framework used in real-world networking:

• Network Access Layer: Combines OSI’s Physical and Data Link layers (e.g., Ethernet).
• Internet Layer: Matches OSI’s Network layer, handling IP addressing/routing.
• Transport Layer: Aligns with OSI’s Transport layer (TCP, UDP).
• Application Layer: Merges OSI’s Session, Presentation, and Application layers (e.g., HTTP).
  Unlike the theoretical OSI model, TCP/IP is streamlined for implementation, powering the internet.

3. What is an IP address, and how do IPv4 and IPv6 differ?

An IP address uniquely identifies devices on a network.

• IPv4: 32-bit, decimal format (e.g., 192.168.1.1), ~4.3 billion addresses, nearing exhaustion.
• IPv6: 128-bit, hexadecimal (e.g., 2001:0db8::1), 340 undecillion addresses, supports auto-configuration and eliminates NAT dependency.
  IPv6 is critical in 2025 for IoT and global connectivity.

4. What is subnetting, and why is it important?

Subnetting divides a large IP network into smaller subnets using a subnet mask (e.g., 255.255.255.0). It optimizes IP allocation, reduces broadcast traffic, and enhances security by segmenting networks (e.g., separating HR and IT VLANs). Example: 192.168.1.0/24 split into 192.168.1.0/25 and 192.168.1.128/25 yields 126 hosts per subnet.

5. What is the difference between a hub and a switch?

• Hub: Layer 1 device, broadcasts data to all ports, causing collisions and inefficiency.
• Switch: Layer 2 device, forwards frames to specific devices using MAC addresses, supporting VLANs and reducing congestion.
  Switches dominate modern LANs for performance and scalability.

6. What is a MAC address, and what is its role?

A Media Access Control (MAC) address is a 48-bit, hexadecimal identifier (e.g., 00:1A:2B:3C:4D:5E) embedded in a network interface card (NIC). It operates at the Data Link layer, ensuring accurate frame delivery within a local network.

7. What is ARP, and how does it function?

Address Resolution Protocol (ARP) maps an IP address to a MAC address in a LAN. A device broadcasts an ARP request (“Who has 192.168.1.10?”), and the target responds with its MAC address, stored in the ARP table for efficient communication.

8. What is DNS, and why is it essential?

Domain Name System (DNS) translates domain names into IP addresses, enabling user-friendly internet navigation without memorizing numerical addresses.

9. What is DHCP, and how does it streamline network management?

Dynamic Host Configuration Protocol (DHCP) automatically assigns IP addresses, subnet masks, gateways, and DNS servers from a pool, reducing manual configuration, preventing IP conflicts, and simplifying network scaling.

10. What are VLANs, and what are their benefits?

Virtual Local Area Networks (VLANs) logically segment devices on the same physical network, improving:

• Security: Isolates sensitive traffic (e.g., VLAN 10 for finance).
• Performance: Reduces broadcast domains.
• Management: Organizes networks (configured via vlan 10, name FINANCE).

11. What is a default gateway?

A default gateway (e.g., 192.168.1.1) is a router’s IP address that devices use to send traffic outside their local network, serving as the gateway to other networks or the internet.

12. What is a broadcast domain?

A broadcast domain is a network segment where broadcast packets reach all devices, typically bounded by routers or VLANs. VLANs reduce broadcast traffic for efficiency.

Routing Essentials

13. What is a router, and how does it function?

A router is a Layer 3 device that forwards packets between networks using IP addresses. It uses routing tables and protocols (e.g., OSPF, RIP) to determine optimal paths, connecting LANs to WANs or the internet.

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

• Static Routing: Manually configured routes (e.g., ip route 192.168.2.0 255.255.255.0 192.168.1.2), ideal for small, stable networks.
• Dynamic Routing: Uses protocols like OSPF or RIP to automatically update routes, suited for large, dynamic networks.

15. What is OSPF, and how does it work?

Open Shortest Path First (OSPF) is a link-state routing protocol using Dijkstra’s algorithm to calculate the shortest path. It maintains a topology database, converges quickly, and scales well for enterprise networks.

16. What is RIP, and what are its limitations?

Routing Information Protocol (RIP) is a distance-vector protocol using hop count. Limitations:

• Maximum 15 hops, limiting network size.
• Slow convergence compared to OSPF.
• Less scalable for modern networks.

17. What is EIGRP, and what makes it unique?

Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco proprietary hybrid protocol combining distance-vector and link-state features. It offers fast convergence, low bandwidth usage, and supports IPv4/IPv6 via DUAL.

18. What is a routing table, and what does it contain?

A routing table lists paths to network destinations, including:

• Destination network (e.g., 192.168.2.0).
• Next hop or interface.
• Metric (e.g., hop count).
• Protocol source (e.g., OSPF).
  View with show ip route.

19. What is the difference between IGP and EGP?

• Interior Gateway Protocol (IGP): Operates within an autonomous system (e.g., OSPF, RIP).
• Exterior Gateway Protocol (EGP): Manages routing between autonomous systems (e.g., BGP for internet).

20. What is a default route?

A default route (e.g., ip route 0.0.0.0 0.0.0.0 192.168.1.1) directs traffic to a gateway when no specific route exists, commonly used for internet access.

21. What is route summarization?

Route summarization combines multiple routes into one (e.g., 192.168.1.0/24 and 192.168.2.0/24 into 192.168.0.0/22), reducing routing table size and improving efficiency.

22. What is the show ip route command used for?

Displays the routing table, showing destination networks, next hops, metrics, and administrative distances, aiding in routing troubleshooting.

23. What is administrative distance?

A value (0–255) ranking routing protocol reliability (e.g., static = 1, OSPF = 110). Lower values are preferred when multiple protocols offer routes.

24. What is a floating static route?

A static route with a higher administrative distance (e.g., ip route 192.168.2.0 255.255.255.0 192.168.1.2 200), used as a backup if dynamic routes fail.

Switching Technologies

25. What is a switch, and how does it operate?

A switch is a Layer 2 device that forwards frames based on MAC addresses using a MAC address table, creating collision-free, efficient LAN communication.

26. What is the difference between a switch and a bridge?

• Switch: Hardware-based, multi-port, supports VLANs, faster.
• Bridge: Software-based, fewer ports, slower, less common today.
  Switches are advanced, scalable bridges.

27. What is a collision domain, and how does a switch affect it?

A collision domain is a segment where simultaneous transmissions cause collisions. Switches create a separate collision domain per port, eliminating collisions.

28. What is a broadcast domain, and how does a VLAN affect it?

A broadcast domain is where broadcast packets reach all devices. VLANs segment broadcast domains, reducing traffic and enhancing performance.

29. How do you configure a VLAN on a Cisco switch?

Steps:

1. Enter config mode: configure terminal.
2. Create VLAN: vlan 10.
3. Name VLAN: name SALES.
4. Assign ports: interface fa0/1, switchport mode access, switchport access vlan 10.

30. What is VTP, and what are its modes?

VLAN Trunking Protocol (VTP) synchronizes VLAN configurations across switches. Modes:

• Server: Creates/modifies VLANs, propagates changes.
• Client: Receives updates, cannot modify.
• Transparent: Maintains local VLANs, forwards updates.

31. What is a trunk port?

A trunk port carries multiple VLANs’ traffic between switches or devices using tagging (e.g., 802.1Q). Configured with switchport mode trunk.

32. What is the Spanning Tree Protocol (STP)?

STP prevents switching loops in redundant topologies by blocking redundant paths, ensuring a single active path using a root bridge.

33. What is a root bridge in STP?

The root bridge, elected by lowest Bridge ID (priority + MAC address), is the reference point for STP path calculations.

34. What is the difference between access and trunk ports?

• Access Port: Carries one VLAN’s traffic for end devices (switchport mode access).
• Trunk Port: Carries multiple VLANs with tagging (switchport mode trunk).

35. What is EtherChannel, and why is it used?

EtherChannel bundles multiple physical links into a logical link, increasing bandwidth and redundancy. Configured with channel-group 1 mode active.

36. What is the show mac address-table command used for?

Displays the switch’s MAC address table, mapping MAC addresses to ports, aiding in connectivity troubleshooting.

IP Addressing and Subnetting

37. What is a subnet mask, and how is it used?

A subnet mask (e.g., 255.255.255.0 or /24) divides an IP address into network and host portions, defining subnet scope for routing.

38. What are private IP address ranges?

Non-routable on the public internet:

• Class A: 10.0.0.0–10.255.255.255 (/8).
• Class B: 172.16.0.0–172.31.255.255 (/12).
• Class C: 192.168.0.0–192.168.255.255 (/16).

39. What is CIDR, and how does it work?

Classless Inter-Domain Routing (CIDR) uses variable-length subnet masks (e.g., /24) for flexible IP allocation, replacing classful addressing (A, B, C).

40. How do you calculate the number of hosts in a subnet?

Formula: 2^(32 - subnet mask bits) - 2. Example: /26 (255.255.255.192) yields 2^(32-26) - 2 = 62 usable hosts.

41. What is a network address?

The first address in a subnet (e.g., 192.168.1.0/24), used to identify the subnet, not assigned to devices.

42. What is a broadcast address?

The last address in a subnet (e.g., 192.168.1.255/24), used to send packets to all subnet devices.

43. What is APIPA?

Automatic Private IP Addressing (APIPA) assigns IPs (169.254.0.1–169.254.255.254) when DHCP fails, enabling local communication.

44. What is NAT, and how does it work?

Network Address Translation (NAT) maps private IPs to public IPs for internet access. Types:

• Static NAT: One-to-one mapping.
• Dynamic NAT: Uses a public IP pool.
• PAT: Maps multiple private IPs to one public IP using ports.
  Example: ip nat inside source static 192.168.1.10 203.0.113.10.

45. What is the difference between public and private IP addresses?

• Public: Globally unique, routable (e.g., 203.0.113.10).
• Private: Non-routable, for internal networks (e.g., 192.168.1.10).

46. How do you configure NAT on a Cisco router?

Steps:

1. Define interfaces: interface fa0/0, ip nat inside; interface fa0/1, ip nat outside.
2. Create NAT rule: ip nat inside source list 1 interface fa0/1 overload.
3. Define ACL: access-list 1 permit 192.168.1.0 0.0.0.255.

47. What is a loopback address?

A virtual address (e.g., 127.0.0.1) for testing and internal device communication, always up unless the device is down.

48. What is the show ip arp command used for?

Displays the ARP table, mapping IPs to MAC addresses, aiding in local network connectivity troubleshooting.

Transport Layer Protocols

49. What is the difference between TCP and UDP?

• TCP: Connection-oriented, reliable, with error checking and retransmission (e.g., HTTP, FTP).
• UDP: Connectionless, faster, no error recovery (e.g., DNS, streaming).

50. What is a TCP three-way handshake?

Establishes a reliable connection:

1. Client sends SYN.
2. Server responds with SYN-ACK.
3. Client sends ACK.
   Ensures both devices are ready to communicate.

51. What are port numbers, and how are they used?

Port numbers (0–65535) identify services on a device (e.g., HTTP: 80, HTTPS: 443). They enable multiplexing multiple services over one IP.

52. What is flow control in TCP?

Flow control regulates data transmission rates using sliding windows to prevent overwhelming the receiver, ensuring reliable delivery.

53. What is the purpose of sequence numbers in TCP?

Sequence numbers track data segment order, ensuring correct reassembly and detecting missing packets.

54. What is the difference between well-known and ephemeral ports?

• Well-Known Ports: 0–1023, reserved for standard services (e.g., HTTP: 80).
• Ephemeral Ports: 1024–65535, dynamically assigned for temporary client connections.

55. What is UDP’s primary advantage?

UDP’s low overhead and lack of connection setup make it faster, ideal for real-time applications like VoIP where minor packet loss is acceptable.

56. What is the show tcp command used for?

Displays TCP connection details (e.g., state, IPs, ports), helping diagnose connectivity issues.

Network Security

57. What is an Access Control List (ACL)?

ACLs filter traffic based on rules for source/destination IPs, ports, or protocols. Types:

• Standard: Filters by source IP (e.g., access-list 10 permit 192.168.1.0 0.0.0.255).
• Extended: Filters by source/destination, port, protocol.

58. How do you secure a Cisco router?

• Set strong passwords: enable secret .
• Enable SSH: ip ssh version 2, crypto key generate rsa.
• Disable Telnet: line vty 0 4, transport input ssh.
• Use ACLs to restrict access.
• Enable logging: logging host .

59. What is a firewall, and how does it work?

A firewall controls traffic based on security rules, operating at Layer 3/4 (e.g., Cisco ASA), blocking unauthorized access while allowing legitimate traffic.

60. What is the difference between symmetric and asymmetric encryption?

• Symmetric: One key for encryption/decryption (e.g., AES), faster but risky for key sharing.
• Asymmetric: Public/private key pairs (e.g., RSA), secure but slower, used for authentication.

61. What is a VPN, and how does it ensure security?

A Virtual Private Network (VPN) creates encrypted tunnels over the internet using protocols like IPsec or SSL, ensuring data confidentiality, integrity, and authentication.

62. What is port security on a switch?

Port security restricts switch port access to specific MAC addresses, preventing unauthorized devices. Configured with switchport port-security maximum 2.

63. What is 802.1X, and how does it enhance security?

802.1X authenticates devices via RADIUS/TACACS+ before granting network access, preventing unauthorized connections.

64. What is the difference between WPA2 and WPA3?

• WPA2: Uses AES, robust but vulnerable to brute-force attacks.
• WPA3: Stronger encryption (SAE protocol), protects against offline attacks, standard for 2025 Wi-Fi.

Wireless Networking

65. What is an SSID, and how is it used?

Service Set Identifier (SSID) is a Wi-Fi network’s name, broadcasted to identify it to clients. Multiple SSIDs can support different networks (e.g., Guest vs. Corporate).

66. What is the difference between 2.4 GHz and 5 GHz Wi-Fi bands?

• 2.4 GHz: Longer range, more interference, supports older devices (802.11b/g/n).
• 5 GHz: Faster, less interference, shorter range (802.11a/n/ac/ax).

67. What is a wireless access point (WAP)?

A WAP connects wireless devices to a wired network, acting as a bridge, configured with SSIDs and security protocols.

68. What is a wireless controller?

A wireless controller centrally manages WAPs, handling configuration, security, and roaming for seamless enterprise Wi-Fi.

69. What is the difference between ad-hoc and infrastructure modes in Wi-Fi?

• Ad-Hoc: Devices connect directly without a WAP.
• Infrastructure: Devices connect via a WAP, common in enterprise/home networks.

70. How does channel overlap affect Wi-Fi performance?

Overlapping channels (e.g., 1, 6, 11 in 2.4 GHz) cause interference, reducing throughput. Non-overlapping channels optimize performance.

71. What is QoS in wireless networking?

Quality of Service (QoS) prioritizes traffic (e.g., VoIP over downloads) to ensure low latency and reliable performance in congested Wi-Fi networks.

72. What is the role of beacons in Wi-Fi?

Beacons are periodic signals from WAPs announcing their presence, SSID, and capabilities, helping devices discover networks.

IP Services

73. What is SNMP, and how is it used?

Simple Network Management Protocol (SNMP) monitors and manages devices, collecting data (e.g., bandwidth) via agents and managers. Versions: SNMPv1, v2c, v3 (secure).

74. What is NTP, and why is it important?

Network Time Protocol (NTP) synchronizes clocks across devices for accurate timestamps in logs, security, and coordination (e.g., ntp server 0.pool.ntp.org).

75. What is syslog, and how does it aid troubleshooting?

Syslog collects and stores device logs, enabling centralized monitoring and analysis for debugging (e.g., logging host 192.168.1.100).

76. What is the show running-config command used for?

Displays the current configuration (interfaces, routing, security), aiding in auditing and troubleshooting.

77. What is HSRP, and how is it configured?

Hot Standby Router Protocol (HSRP) provides router redundancy. Configuration:

1. Primary router: standby 1 ip 192.168.1.1, standby 1 priority 110.
2. Backup router: standby 1 ip 192.168.1.1.
   Ensures failover if the primary fails.

78. What is VRRP, and how does it compare to HSRP?

Virtual Router Redundancy Protocol (VRRP) is an open-standard alternative to HSRP, offering similar failover with simpler configuration and broader vendor support.

79. What is ICMP, and what is its role?

Internet Control Message Protocol (ICMP) handles error messages and diagnostics (e.g., ping, traceroute), aiding in connectivity testing.

80. What is the difference between ping and traceroute?

• Ping: Tests reachability and round-trip time via ICMP echo requests.
• Traceroute: Maps packet paths, showing hops and latency.

Troubleshooting Techniques

81. How do you troubleshoot network connectivity issues?

Steps:

1. Check physical connections (cables, LEDs).
2. Verify IP settings: show ip interface brief.
3. Test reachability: ping .
4. Trace path: traceroute .
5. Check logs: show logging.
6. Verify ACLs/firewalls.

82. What does the show ip interface brief command do?

Displays interface status (up/down), IP addresses, and operational state, helping identify configuration issues.

83. What is a CRC error, and what causes it?

Cyclic Redundancy Check (CRC) errors indicate corrupted frames, caused by faulty cables, interference, or duplex mismatches.

84. What is the purpose of the debug command?

Enables real-time monitoring of processes (e.g., debug ip packet), providing insights for troubleshooting, but use cautiously due to CPU impact.

85. What is packet loss, and how do you diagnose it?

Packet loss occurs when packets fail to reach their destination. Diagnose with ping (loss percentage), traceroute (problematic hops), or tools like Wireshark.

86. What does high latency indicate?

High latency (via ping) suggests congestion, long routes, or device performance issues, impacting real-time applications like VoIP.

87. What is the show version command used for?

Displays device details (IOS version, uptime, hardware), aiding in compatibility and troubleshooting.

88. How do you identify a switching loop?

Symptoms: broadcast storms, high CPU usage, duplicate frames. Use show spanning-tree to verify STP and root bridge configuration.

Network Automation and SDN

89. What is Software-Defined Networking (SDN)?

SDN separates the control plane (routing decisions) from the data plane (packet forwarding), enabling centralized management via controllers (e.g., Cisco DNA Center) for programmable networks.

90. What is the role of APIs in network automation?

APIs (e.g., REST, NETCONF) enable programmatic device management, automating configuration, monitoring, and troubleshooting tasks.

91. What is NETCONF, and how does it work?

Network Configuration Protocol (NETCONF) uses XML-based messages to manage and configure devices, supporting automation and consistency.

92. What is the benefit of network programmability in 2025?

Programmability reduces errors, speeds up deployments, and enables scalability for IoT, 5G, and cloud-driven networks.

93. What is Ansible in network automation?

Ansible is an open-source tool using YAML playbooks to automate network device configuration, simplifying repetitive tasks across Cisco and other platforms.

94. What is Cisco DNA Center?

Cisco DNA Center is a centralized platform for network automation, offering policy-based configuration, analytics, and assurance for enterprise networks.

95. What is intent-based networking?

Intent-based networking translates business objectives into automated network policies, ensuring alignment with goals via platforms like Cisco DNA.

96. What is the difference between traditional and programmable networks?

• Traditional: Manual, device-by-device configuration, error-prone.
• Programmable: Automated, centralized management via APIs/SDN, scalable.

Advanced Routing and Switching

97. What is BGP, and when is it used?

Border Gateway Protocol (BGP) is an external routing protocol for exchanging routes between autonomous systems, critical for internet and large enterprise networks.

98. What is the difference between OSPF areas and stub areas?

• OSPF Areas: Divide networks for scalability (e.g., Area 0 backbone).
• Stub Areas: Limit external routes, reducing routing table size for smaller networks.

99. What is a designated router (DR) in OSPF?

The DR, elected by priority or router ID, manages link-state updates in multi-access networks, reducing OSPF traffic.

100. What is LACP, and how does it enhance EtherChannel?

Link Aggregation Control Protocol (LACP) dynamically negotiates EtherChannel links, ensuring redundancy and load balancing.

101. What is MSTP, and why is it used?

Multiple Spanning Tree Protocol (MSTP) maps multiple VLANs to a single spanning tree instance, optimizing redundancy and scalability over traditional STP.

102. What is a VRF, and how is it used?

Virtual Routing and Forwarding (VRF) creates separate routing tables on a device, enabling segmentation for multi-tenant or VPN environments.

103. What is the show ip bgp command used for?

Displays BGP routing details (neighbors, prefixes, path attributes), aiding in inter-domain routing troubleshooting.

104. What is route redistribution?

Route redistribution shares routes between different routing protocols (e.g., OSPF to RIP), ensuring connectivity across diverse network segments.

WAN Technologies

105. What is Frame Relay, and how does it work?

Frame Relay is a Layer 2 WAN protocol using virtual circuits (DLCIs) for cost-effective, high-performance connectivity, though largely replaced by MPLS.

106. What is MPLS, and why is it used?

Multiprotocol Label Switching (MPLS) uses labels to route packets efficiently across WANs, supporting QoS, VPNs, and traffic engineering.

107. What is a point-to-point link?

A point-to-point link connects two devices directly (e.g., serial or Ethernet), used in WANs for dedicated, high-speed connections.

108. What is the difference between leased lines and VPNs?

• Leased Lines: Dedicated physical circuits, reliable but expensive (e.g., T1).
• VPNs: Virtual tunnels over the internet, cost-effective but rely on public infrastructure.

109. What is PPP, and how is it configured?

Point-to-Point Protocol (PPP) provides authentication and encapsulation for WAN links. Configuration: interface serial0/0/0, encapsulation ppp, ppp authentication chap.

110. What is the role of GRE tunnels?

Generic Routing Encapsulation (GRE) creates virtual point-to-point links over IP networks, encapsulating protocols for flexible, secure connectivity.

111. What is DMVPN?

Dynamic Multipoint VPN (DMVPN) enables scalable, dynamic VPNs with spoke-to-spoke communication, ideal for large branch networks.

112. What is the show interface command used for?

Displays interface statistics (status, bandwidth, errors), critical for diagnosing WAN and LAN issues.

IPv6 and Modern Networking

113. Why is IPv6 adoption critical in 2025?

IPv6’s vast address space (340 undecillion) supports IoT, 5G, and global connectivity, overcoming IPv4’s exhaustion and reducing NAT reliance.

114. What is the structure of an IPv6 address?

128-bit, eight hexadecimal groups (e.g., 2001:0db8:85a3:0000:0000:8a2e:0370:7334). Shorthand: omit leading zeros, compress consecutive zeros (:: once).

115. What is stateless address autoconfiguration (SLAAC) in IPv6?

SLAAC enables devices to self-configure IPv6 addresses using router advertisements, simplifying deployment without DHCP.

116. What is the difference between IPv6 link-local and global addresses?

• Link-Local: Auto-assigned (FE80::/10), for local communication.
• Global: Routable worldwide, assigned via SLAAC, DHCPv6, or manually.

117. What is the show ipv6 interface command used for?

Displays IPv6 interface details (addresses, link-local status, protocols), aiding in IPv6 troubleshooting.

118. What is neighbor discovery protocol (NDP) in IPv6?

NDP replaces ARP in IPv6, handling address resolution, router discovery, and duplicate address detection via ICMPv6.

119. What is EUI-64 in IPv6?

Extended Unique Identifier-64 generates an IPv6 interface ID by inserting FFFE into a MAC address and flipping the 7th bit, used in SLAAC.

120. What are the benefits of IPv6 over IPv4?

Larger address space, simplified header, no NAT, built-in IPsec, and support for IoT and 5G applications.

Network Management and Monitoring

121. What is Cisco IOS?

Cisco IOS is the operating system for Cisco devices, managing routing, switching, security, and configuration tasks.

122. What is the difference between ROMMON and IOS?

• ROMMON: Firmware for booting and recovery (e.g., password reset).
• IOS: Full-featured OS for normal device operations.

123. What is the copy running-config startup-config command?

Saves the current configuration to non-volatile memory, ensuring settings persist after reboot.

124. What is a network management station (NMS)?

An NMS collects and analyzes data from devices via SNMP, syslog, or NetFlow, providing centralized monitoring.

125. What is NetFlow, and how is it used?

NetFlow collects IP traffic statistics (e.g., source/destination, volume), aiding in performance monitoring and security analysis.

126. What is the show logging command used for?

Displays system logs (errors, events, alerts), helping diagnose device or network issues.

127. What is the difference between CLI and GUI management?

• CLI: Command-line for precise, scriptable control (e.g., Cisco IOS).
• GUI: Graphical tools (e.g., Cisco DNA Center) for user-friendly management, less flexible.

128. What is a configuration register?

Controls boot behavior (e.g., 0x2102 for normal boot, 0x2142 to bypass startup-config for recovery).

Advanced Security and Redundancy

129. What is AAA, and how is it implemented?

Authentication, Authorization, and Accounting (AAA) secures access:

• Authentication: Verifies identity.
• Authorization: Defines permissions.
• Accounting: Logs actions.
  Implemented via RADIUS/TACACS+ (e.g., aaa new-model, radius-server host 192.168.1.100).

130. What is the difference between RADIUS and TACACS+?

• RADIUS: Open standard, combines authentication/authorization, for network access.
• TACACS+: Cisco proprietary, separates AAA, for device administration.

131. What is IPsec, and how does it secure VPNs?

IPsec provides encryption, authentication, and integrity for VPNs using ESP (data encryption) and AH (authentication).

132. What is a zone-based firewall?

Zone-Based Policy Firewall (ZBFW) groups interfaces into zones, applying security policies to control inter-zone traffic, offering flexibility over ACLs.

133. What is GLBP, and how does it differ from HSRP?

Gateway Load Balancing Protocol (GLBP) provides redundancy and load balancing across multiple gateways, unlike HSRP’s single active router.

134. What is the role of a crypto map in IPsec VPNs?

A crypto map defines IPsec policies (e.g., encryption, peers) and applies them to interfaces (e.g., crypto map MYMAP 10 ipsec-isakmp).

135. What is the show crypto isakmp sa command used for?

Displays active ISAKMP security associations for IPsec VPNs, showing tunnel status and encryption details.

136. What is a DDoS attack, and how can it be mitigated?

A Distributed Denial of Service (DDoS) attack overwhelms networks with traffic. Mitigation:

• Rate limiting.
• ACL-based traffic filtering.
• DDoS protection services.
• Redundant infrastructure.

Practical Cisco Configurations

137. How do you configure a static route on a Cisco router?

ip route 192.168.2.0 255.255.255.0 192.168.1.2 directs traffic for 192.168.2.0/24 to the next hop.

138. How do you configure OSPF on a Cisco router?

Steps:

1. Enable OSPF: router ospf 1.
2. Define networks: network 192.168.1.0 0.0.0.255 area 0.
3. Set router ID: router-id 1.1.1.1.

139. How do you configure a trunk port on a Cisco switch?

interface fa0/1, switchport mode trunk, switchport trunk allowed vlan 10,20 enables VLANs 10 and 20.

140. How do you configure port security on a Cisco switch?

interface fa0/1, switchport mode access, switchport port-security, switchport port-security maximum 2, switchport port-security mac-address .

141. How do you configure SSH on a Cisco device?

Steps:

1. Set hostname: hostname R1.
2. Configure domain: ip domain-name example.com.
3. Generate RSA key: crypto key generate rsa.
4. Enable SSH: line vty 0 4, transport input ssh.

142. How do you configure a basic ACL?

access-list 10 permit 192.168.1.0 0.0.0.255, applied with interface fa0/0, ip access-group 10 in.

143. How do you configure a GRE tunnel?

Steps:

1. Create tunnel: interface tunnel 0.
2. Set IPs: ip address 10.0.0.1 255.255.255.0.
3. Define source/destination: tunnel source fa0/0, tunnel destination 203.0.113.2.

144. How do you configure VLAN trunking with 802.1Q?

interface fa0/1, switchport mode trunk, switchport trunk encapsulation dot1q enables 802.1Q tagging.

Emerging Trends and Miscellaneous

145. What is the role of IoT in modern networking?

IoT devices (e.g., smart sensors) drive demand for IPv6, low-latency protocols, and robust security in 2025 networks.

146. What is 5G’s impact on networking?

5G offers high-speed, low-latency connectivity, enabling applications like autonomous vehicles and requiring advanced QoS and edge computing.

147. What is network slicing in 5G?

Network slicing creates virtual networks on shared 5G infrastructure, tailoring performance for specific use cases (e.g., IoT vs. streaming).

148. What is the role of AI in networking?

AI optimizes routing, predicts failures, and automates configurations via platforms like Cisco DNA Center, enhancing efficiency in 2025.

149. What is zero-trust architecture?

Zero-trust assumes no device/user is trusted, requiring continuous authentication and verification, critical for modern cyber threats.

150. What is the difference between SDN and NFV?

• SDN: Separates control and data planes for programmable networks.
• NFV: Virtualizes network functions (e.g., firewalls) on commodity hardware.

151. What is Cisco Packet Tracer?

Packet Tracer is a simulation tool for designing, configuring, and troubleshooting networks, ideal for CCNA practice.

152. What are top skills for CCNA professionals in 2025?

• Routing/switching (OSPF, VLANs).
• IPv6 configuration.
• Network automation (Python, Ansible).
• Security (ACLs, VPNs, zero-trust).
• Cloud and SDN familiarity.

Tips for Acing Your CCNA Interview

• Hands-On Practice: Use Packet Tracer or GNS3 for configurations.
• Master Commands: Explain show ip route, show vlan, etc.
• Stay Current: Know 2025 trends like IPv6, SDN, and zero-trust.
• Communicate Clearly: Simplify technical concepts for interviewers.
• Resources: Study Cisco’s official guides and practice with industry-standard tools.