CCNA Training in Chennai

Q1. What is the OSI model, and why is it important?

Answer: The OSI (Open Systems Interconnection) model has 7 layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application. It standardizes how devices communicate across a network and is the reference framework for troubleshooting, design, and vendor interoperability.

Interview Tip: Memorize a mnemonic like "Please Do Not Throw Sausage Pizza Away" and explain a real scenario such as an HTTP request flowing through the layers.

Q2. What is the difference between TCP and UDP?

Answer: TCP (Transmission Control Protocol) is connection-oriented, provides reliable delivery through acknowledgments and retransmission, and is used by HTTP, FTP, and SSH. UDP (User Datagram Protocol) is connectionless, faster, and used by DNS, DHCP, VoIP, and streaming where speed matters more than reliability.

Q3. What is the difference between a Hub, Switch, and Router?

Answer: A Hub broadcasts all traffic to every port (Layer 1). A Switch forwards traffic based on MAC addresses to the correct port only (Layer 2). A Router routes traffic between different networks using IP addresses (Layer 3). In modern networks, hubs are obsolete and switches/routers are standard.

Q4. What is a collision domain and a broadcast domain?

Answer: A collision domain is a network segment where frames can collide (hubs share one collision domain; each switch port is its own). A broadcast domain is a segment where broadcast frames are received by all devices. Routers separate broadcast domains; switches separate collision domains.

Q5. What is the purpose of ARP?

Answer: ARP (Address Resolution Protocol) resolves an IP address to a MAC address on a local network. When a device wants to send traffic to an IP address on the same subnet, it sends an ARP broadcast asking "Who has this IP?" and the target replies with its MAC address.

Q1. What is subnetting, and why is it used?

Answer: Subnetting divides a larger network into smaller sub-networks to improve security, reduce broadcast traffic, and use IP address space efficiently. For example, a /24 network can be divided into multiple /26 subnets for different departments.

Q2. What is the difference between a subnet mask and CIDR notation?

Answer: A subnet mask (e.g., 255.255.255.0) and CIDR notation (e.g., /24) both define the network portion of an IP address. CIDR is a shorthand notation showing the number of network bits. They represent the same information in different formats.

Q3. What are private IP address ranges?

Answer: Private ranges defined in RFC 1918 are: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. These are not routed on the public internet and are used inside organizations. NAT translates private to public IPs for internet access.

Q4. How many usable hosts does a /28 subnet have?

Answer: A /28 has 4 host bits, giving 2&sup4; = 16 addresses. Subtract network and broadcast addresses: 16 − 2 = 14 usable hosts. This type of quick calculation is tested frequently in CCNA interviews.

Q1. What is a VLAN, and why is it used?

Answer: A VLAN (Virtual LAN) logically segments a physical network into separate broadcast domains without requiring additional hardware. VLANs improve security, reduce broadcast traffic, and simplify network management by grouping devices by function regardless of physical location.

Q2. What is the difference between an access port and a trunk port?

Answer: An access port carries traffic for a single VLAN and connects end devices like PCs or phones. A trunk port carries traffic for multiple VLANs using 802.1Q tagging and connects switches, routers, or access points that need to pass VLAN information.

Q3. What is Spanning Tree Protocol (STP)?

Answer: STP prevents Layer 2 loops in redundant switch topologies by placing redundant paths in a blocking state. It elects a Root Bridge and calculates the best path to it. Without STP, broadcast storms and MAC table instability would cause network failure.

Q4. What is inter-VLAN routing?

Answer: Inter-VLAN routing allows traffic to flow between different VLANs through a Layer 3 device. Methods include Router-on-a-Stick (one physical interface with sub-interfaces) or a Layer 3 switch with Switched Virtual Interfaces (SVIs).

Q1. What is the difference between static and dynamic routing?

Answer: Static routes are manually configured by the administrator and do not change automatically. Dynamic routing protocols like OSPF and EIGRP automatically discover and update routes when network topology changes. Dynamic routing is preferred for large, complex networks.

Q2. What is OSPF, and how does it work?

Answer: OSPF (Open Shortest Path First) is a link-state routing protocol that uses Dijkstra's algorithm to calculate the shortest path. Routers exchange LSAs (Link-State Advertisements), build a topology database, and elect a DR/BDR on multi-access networks. It scales well and supports VLSM/CIDR.

Q3. What is administrative distance?

Answer: Administrative Distance (AD) is a value that routers use to select the best route when multiple routing sources provide a path to the same destination. Lower AD is preferred. Direct (0), Static (1), EIGRP (90), OSPF (110), RIP (120).

Q4. What is the difference between EIGRP and OSPF?

Answer: EIGRP is a Cisco proprietary hybrid protocol using DUAL algorithm; OSPF is an open standard link-state protocol. EIGRP converges faster and is simpler to configure for smaller Cisco-only networks. OSPF is preferred for multi-vendor environments and scales better for large networks.

Q1. How do you troubleshoot a network connectivity issue?

Answer: Use a layered OSI approach: (1) Check physical connectivity and interface status. (2) Verify Layer 2 with show mac-address-table and show interfaces. (3) Check routing table and IP reachability with ping and traceroute. (4) Verify ACLs and security policies. (5) Check application-layer services. Document each step.

Q2. What is an ACL in networking?

Answer: An ACL (Access Control List) is a set of rules that filters network traffic based on source/destination IP, protocol, and port. Standard ACLs filter by source IP only. Extended ACLs filter by source, destination, protocol, and port for granular control.

Q3. What is the difference between SSH and Telnet?

Answer: Telnet sends data in plain text and is insecure. SSH encrypts all communication and is the secure standard for remote device management. In modern networks, Telnet is disabled and SSH is mandatory for Cisco device access.

Q4. What is NAT and why is it used?

Answer: NAT (Network Address Translation) translates private IP addresses to a public IP address for internet access. PAT (Port Address Translation) allows many internal devices to share one public IP using different port numbers. NAT conserves public IP address space.

Q1. Tell me about yourself.

Sample Answer: “I completed a CCNA training program with hands-on practice in routing, switching, Cisco IOS, VLANs, OSPF, ACL security, and network troubleshooting using Packet Tracer and GNS3. I enjoy solving complex network problems and want to grow as a network engineer delivering reliable infrastructure.”

Q2. Why do you want to work in networking?

Sample Answer: “Networking is the foundation of every digital system. I enjoy the logical challenge of designing reliable networks and the satisfaction of diagnosing and fixing connectivity issues quickly and systematically.”

Q3. How do you stay updated with networking technologies?

Sample Answer: “I follow Cisco's official resources, practice in Packet Tracer, read networking blogs, and study for higher certifications like CCNP. I also practice troubleshooting scenarios regularly to keep my skills sharp.”