CCNA Interview Questions and Answers

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

The OSI (Open Systems Interconnection) model is a conceptual framework used to understand network interactions in seven layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application. It's important because it helps network professionals standardize hardware and software, ensuring different network devices and protocols can work together.

What is the difference between TCP and UDP?

TCP (Transmission Control Protocol) is a connection-oriented protocol that ensures the reliable delivery of data packets in the exact order they were sent. UDP (User Datagram Protocol) is connectionless, does not guarantee delivery, and does not maintain order, making it faster but less reliable than TCP.

Explain the function of a router.

A router is a network device that forwards data packets between computer networks. It routes the data based on their IP addresses and performs traffic directing functions on the Internet. Routers operate at the network layer (Layer 3) of the OSI model.

What is a subnet mask?

A subnet mask is a number that outlines a range of IP addresses in a network. It separates the IP address into the network and host address. By using a subnet mask, we can determine which part of the IP address refers to the network and which part refers to the node.

Define what VLAN is and its purpose.

VLAN (Virtual Local Area Network) is a technology that creates separate, isolated networks within a single physical network infrastructure. Its purpose is to improve network efficiency and security by segmenting networks into smaller parts, reducing broadcast domains, and segregating network traffic.

Explain the difference between a hub, switch, and router.

A hub is a basic networking device that connects multiple computers or other network devices together, forwarding data to all connected devices. A switch is more advanced, connecting devices and forwarding data only to the intended recipient based on MAC addresses. A router connects multiple networks together, routing data between them based on IP addresses.

What are collision domains and broadcast domains?

A collision domain is a network segment where data packets can collide with each other when being sent on a shared medium. A broadcast domain is a logical division of a computer network, within which a broadcast frame can be sent to all devices. Switches separate collision domains, while routers separate broadcast domains.

Explain NAT and its purpose.

NAT (Network Address Translation) is a process used in routers to translate private (not globally unique) IP addresses into a public IP address and vice versa. The purpose of NAT is to improve security and reduce the number of IP addresses an organization needs.

What is DHCP and why is it used?

DHCP (Dynamic Host Configuration Protocol) is a network management protocol used to dynamically assign IP addresses and other network configuration parameters to devices on a network, ensuring that devices can communicate effectively without manual setup.

Describe what a routing table is.

A routing table is a set of rules, often viewed as a table, stored in a router or a networked computer. It lists the routes to particular network destinations, including the interfaces through which the packets will be sent.

What is the purpose of the ping command?

The ping (Packet Internet Groper) command is a diagnostic tool used to test the connectivity between two nodes or devices across a network. It helps in determining whether a specific IP address is accessible.

Explain the concept of a default gateway.

A default gateway serves as an access point or IP router that a networked computer uses to send information to a computer in another network or the internet when no other route specification matches the destination IP address of the packets.

What are ACLs and how are they used?

ACLs (Access Control Lists) are a series of commands that are used to filter traffic based on IP addresses, protocols, or port numbers on Cisco routers and switches. They are used to increase network security by controlling which packets are allowed or denied in a network.

What is the purpose of STP in networking?

STP (Spanning Tree Protocol) is a network protocol that ensures a loop-free topology for any bridged Ethernet local area network. It prevents bridge loops and the broadcast radiation that would result from them.

Describe the difference between static and dynamic routing.

Static routing is a process in which a network administrator manually enters routes into the routing table of a router. Dynamic routing uses algorithms and protocols, such as RIP, OSPF, or EIGRP, to automatically adjust to changes in the network, making it more flexible and scalable than static routing.