CCNA Routing and Switching Interview Questions

If you want to start a career in the network infrastructure industry, pursuing Cisco’s CCNA certification is the best decision you can make. Expanded as Cisco Certified Network Associate (CCNA), it creates a basic foundation for building a solid career as a Network Engineer. 

Whether you’re upskilling from the role of a Desktop Support Engineer or want to start as a Network Engineer, opting for CCNA is mandatory. In fact, 90% of recruiters look for certified candidates. 

Preparing for a CCNA interview? Check out this comprehensive guide on the best CCNA Routing and Switching interview questions along with answers.

CCNA Routing and Switching Interview Questions for Freshers

1. What do you understand by networking?

A network is a collection of computers that can communicate with each other and share information. Networking is the practice of connecting computers, devices or systems to share resources and information. 

The following areas are covered under the networking umbrella:

Types of Computer Networking

• Local Area Network (LAN): Networks limited to a small geographic location, such as a home, office, or campus

• Wide Area Network (WAN): Networks covering large geographic areas, such as the Internet

• Metropolitan Area Network (MAN): Networks that cover a city or large campus

• Personal Area Network (PAN): Small networks for personal devices, usually employing Bluetooth

Key Networking Concepts

• IP Addressing: The process that gives unique addresses to devices on a network

• Routing: Where the data takes its route from source to destination

• Protocols: Instructions that control how devices talk to each other (TCP/IP, HTTP, etc.)

• Network topology: Physical and logical structure of network components

2. What is meant by a routing protocol? What are its important functions?

A routing protocol refers to the set of rules and algorithms used by network devices, especially routers use to talk to each other. It also helps in determining the best path for data to travel across the network.

The following are the most commonly used routing protocols:

• RIP (Routing Information Protocol): A lightweight distance-vector protocol with hop count as its metric

• OSPF (Open Shortest Path First): A link-state protocol that determines the shortest paths from the total link cost accumulation

• BGP (Border Gateway Protocol): Operated mostly between various autonomous systems on the web

• EIGRP (Enhanced Interior Gateway Routing Protocol): A Cisco-owned protocol that integrates the features of distance-vector and link-state protocols

The following are the most important functions of routing protocols:

• Deciding the optimal path

You can use a routing protocol to calculate optimal routes for data packets. This can be accomplished based on the following metrics:

1. Hop count

2. Bandwidth

3. Delay

4. Reliability

• Convergence

Routing protocols can adapt to network changes such as failed links or added routers. These protocols do so by updating routing tables.

• Exchanging information 

Routers use routing protocols to share information and knowledge about network structure and connectivity between them in a network topology.

• Prevention of loops

The routing protocols make sure that the data packets do not revolve around a network endlessly.

3. Explain the difference between a router and a switch.

4. What are VLANs and why are they used?

A VLAN, or Virtual Local Area Network, is a group of network topologies that consist of devices that are in different locations physically. You must note that these devices can be remote in position but still act similarly. VLANs are local subdivisions of a switch.

They used to do the following:

• To improve security through traffic segregation

• To minimise broadcast domains

• Networks should be structured by department, function, or project

• To minimise network management

• Performance improvement through the elimination of unnecessary traffic

5. What is the role of the ARP protocol?

Address Resolution Protocol (ARP) is a protocol that converts IP addresses to MAC addresses. Here’s the process of how this happens:

1. Whenever a device wants to communicate with another device on the local network, it needs the MAC address of the device to create a properly formatted frame. 

2. A broadcast message is sent by the ARP protocol asking, "Who has this IP?" and the device with that IP responds with its MAC address.

6. What is meant by default gateway? Why is it important?

A default gateway is the router interface to which devices forward packets when they attempt to reach addresses on foreign networks. It is significant because without it, devices can only exchange data within their own local network. The default gateway sets the path for devices to exchange data with foreign networks, such as the Internet.

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

8. What is the function of a spanning tree protocol (STP)?

The main role of the STP protocol is to prevent loops in switched networks. It does so by doing the following:

• Detection of redundant links in the network

• Shutting down some of those links to form a loop-free logical topology

• Provisionally reconfiguring the network in case of link failure

If STP were not there, broadcast storms would happen, leading to serious network congestion and breakdowns in cases of redundant links.

9. What is DHCP? How Does it Work?

Commonly called as DHCP, Dynamic Host Configuration Protocol plays the role of automatically assigning IP addresses and other important network configuration parameters such as IP addressing, network protocols, hostname, network topology, bandwidth and more.

This process follows a four-step exchange, which is commonly called DORA. Here is how it works:

• Discover: Client sends a request for an IP address

• Offer: The DHCP server provides a free IP address

• Request: Client requests the provided IP address

• Acknowledgment: Server acknowledges and completes the assignment

This does away with manually setting IP addresses on every device.

10. What are ACLs? How are they important?

You can consider Access Control Lists (ACLs) as a filter system in a network topology. They are a set of rules that filter traffic based on some specific criteria, such as:

• source/destination IP address

• Port numbers

• Protocols

They’re important for the following reasons:

• They enhance network security by controlling what traffic is allowed

• They can restrict access to sensitive network resources

• They help implement network policies

• They can be used to prioritize certain types of traffic

CCNA Routing and Switching Interview Questions for Experts

11. Explain the difference between distance vector and link-state routing protocols. When would you choose one over the other?

Distance vector routing protocols (e.g., RIP) use a "routing by rumour" approach. Each router only informs its neighbours of its known routes and the associated distance (hop count). They rely on periodic updates, which can lead to slow convergence and routing loops. Link-state routing protocols (e.g., OSPF, IS-IS) build a complete map of the network. Each router floods link-state advertisements (LSAs) containing information about its directly connected links. This allows routers to calculate the shortest path independently.

When it comes to small and stable networks with limited resources, distance vector protocols are a better choice. It is so because they are simpler to configure and thus, suitable for such networks. 

On the other hand, link-state protocols provide faster convergence, better scalability, and loop prevention mechanisms, making them ideal for larger, more complex networks. The choice depends on network size, stability requirements, and available hardware resources.

12. How does Spanning Tree Protocol (STP) prevent loops in a switched network? Explain the process of root bridge election and port states.

STP prevents loops by logically blocking redundant paths in a switched network. It achieves this by electing a root bridge, which acts as the reference point for all other switches. The switch with the lowest bridge ID (priority and MAC address) becomes the root bridge.

The process involves the exchange of Bridge Protocol Data Units (BPDUs). Each switch compares the BPDUs it receives and determines the best path to the root bridge. Ports are then assigned different states:

• Root Port: The port on a non-root bridge with the best path to the root bridge.

• Designated Port: The port on a segment that is deemed to be the best to forward traffic towards the root bridge.

• Blocked Port: A port that is blocked to prevent loops.

Therefore, STP prevents broadcast storms and MAC address table instability by ensuring that a single logical path is active.

13. How VLANs improve network security and performance. What are the different types of VLANs? Name them with a simple explanation.

VLANs (Virtual LANs) segment a physical network into multiple logical networks. This improves security by isolating traffic between VLANs, preventing unauthorised access. They also enhance performance by reducing broadcast traffic within each VLAN, preventing it from flooding the entire network.

Types of VLANs include:

• Data VLAN: Carries user-generated traffic.

• Voice VLAN: Prioritises voice traffic for quality of service.

• Management VLAN: Used for managing network devices.

• Native VLAN: Transports untagged traffic on trunk links.

14. Explain the concept of routing tables and how they are used to forward packets.

A routing table is a database on a router that keeps information regarding known networks and the optimal path to reach them. The destination network, the next-hop IP address, and the metric (cost) of the path are contained in each entry in the routing table.

When a router receives a packet, it consults its routing table. It searches for the most specific route that matches the destination IP address of the packet. The router then forwards the packet to the next-hop IP address specified in the routing table entry. The packet is typically dropped or forwarded to a default gateway if no matching route is identified.

15. Discuss the different types of switching techniques.

There are mainly three different types of switching techniques:

1. Store and forward

2. Cut-through

3. Fragment-free

Each of them is explained one by one as follows:

• Store-and-Forward: The switch receives the entire frame, checks it for errors using the FCS (Frame Check Sequence), and then forwards it. Provides high error detection but higher latency.

• Cut-Through: The switch starts forwarding the frame as soon as it reads the destination MAC address. This lowers latency but forwards potentially faulty frames.

• Fragment-Free: The switch reads the first 64 bytes of the frame before forwarding. This checks for collisions, as most collisions occur within the first 64 bytes. It is a compromise between latency and error checking.

16. What are the advantages and disadvantages of using static routing vs. dynamic routing?

• Static Routing Advantages: Simplicity, security (less prone to routing protocol attacks), predictability. 

• Disadvantages: Manual configuration, lack of adaptability to network changes, and scalability issues.

• Dynamic Routing Advantages: Automatic adaptation to network changes, scalability, and reduced administrative overhead. 

• Disadvantages: Higher complexity, security vulnerabilities, and resource-intensive (CPU, memory).

17. How does OSPF (Open Shortest Path First) handle network changes and ensure fast convergence?

OSPF employs a link-state database to keep an up-to-date map of the network. When a change occurs in the network (e.g., a link goes down), the router detects the change and broadcasts an LSA to all other routers in the area. These routers update their link-state databases and recompute the shortest paths using the SPF algorithm. 

This method provides rapid convergence and reduces interference with network traffic. OSPF also supports areas, which confine the boundary of LSAs and enhance scalability.

18. What is the difference between a collision domain and a broadcast domain?

19. Describe the purpose of QoS (Quality of Service) and how it can be implemented in a network.

QoS ensures that some network traffic gets preferential treatment over other traffic. It assists in prioritizing mission-critical applications such as voice and video to ensure optimal performance even during congestion.

QoS can be achieved through several techniques, such as:

• Classification and Marking: Marking and labelling traffic based on type or priority.

• Queueing: Assigning priority to different queues based on priority.

• Congestion Avoidance: Avoiding congestion by discarding or delaying lower-priority traffic.

• Shaping and Policing: Restricting the amount of bandwidth consumed by certain traffic streams.

20. Explain the role of FHRPs (First Hop Redundancy Protocols) like HSRP, VRRP, and GLBP in achieving high availability.

Multiple routers can share a virtual IP address and a MAC address as a default gateway, as FHRPs provide fault tolerance. 

If the active router fails, it is automatically replaced by a standby router, which reduces downtime and preserves network connectivity.

• HSRP (Hot Standby Router Protocol): This protocol is a Cisco-owned router protocol.

• VRRP (Virtual Router Redundancy Protocol): This router protocol follows an open standard.

• GLBP (Gateway Load Balancing Protocol): This protocol is Cisco's proprietary, i.e., it is owned by Cisco. It provides load balancing between multiple routers rather than simply standby.

These protocols enhance robustness by providing redundancy at the first hop router, making the network available round the clock even when routers fail. They are essential for networks demanding high availability.

Conclusion

Routing and switching concepts form the basic foundation for becoming a Network or Network Security Engineer. In this guide, we have added both routing and switching interview questions for beginners and advanced candidates. We’ve added an updated list of the most commonly asked interview questions. However, you must note that this list is not exhaustive. 

Happy learning!