Hundreds of candidates face Cisco interview questions every year. The skill set required is tested through individual interviews for experienced candidates and mass campus recruitment drives for freshers. Meritorious candidates or those with good academic track records and strong analytical skills, ace the Cisco interview.
In order to qualify, you should have strong fundamentals in networking concepts, which you can acquire with the help of a CCNA certification course. Your expertise in algorithms, data structures, programming languages (like C and C++) and scripting languages (like Perl and python) may add more points too.
Here are 25 top Cisco interview questions to help you prepare thoroughly for your upcoming technical interview:
Cisco interview questions for fresh graduates
If you are a fresher and this is your first interview, prepare the below questions and answers for your technical round in a Cisco interview.
Question #1. What is a link?
Answer: A link is a physical or a logical component of a network which interconnects devices or nodes.
Question #2. What is a node?
Answer: A node is a point of connection within a network for systematic data transmission. A computer or printer or any other type of device capable of sending and receiving data through a network can be called a node.
Question #3. What is a gateway?
Answer: Basically, a gateway is a node of network that can be used as an entrance into some other network. Being a piece of hardware, it is not the same as a default gateway.
Question #4. What is routing?
Answer: Routing is the process of establishing the routes that data packets take on their way to a particular destination. Routing is done with a router, basically a device used to select a path for traffic in a network, or between or across multiple networks. This network topology depends on a setup of hardware, to effectively relay data.
Question #5. What is the purpose of data link layer in TCP/IP or OSI layer?
Answer: Data-Link layer is responsible for transporting data within a network. The Data-link layer packages the higher-layer data into frames. This packaging process is referred to as framing or encapsulation. Data-Link layer has 2 sublayers:
- Logical Link Control (LLC) sublayer
- Media Access Control (MAC) sublayer
Question #6. What are the key advantages of using switches?
Answer: Switches interpret the bits in the received frame so that they can typically send the frame out of the one required port, rather than all other ports. They don’t create a single shared bus like hubs.
Question #7. When does network congestion occur?
Answer: A network congestion basically happens when applications send more data than the network devices (e.g., routers and switches) can handle or accommodate. Thereby causing buffers on these devices to fill up and sometimes overflow.
Here, a buffer is a portion of the memory of a device which is basically set aside as a temporary holding place for data. This data is sent to or received from other devices and the whole process might result in delayed or lost packets. Eventually, applications retransmit the data and end up adding more traffic. This further increases the congestion.
Question #8. What is a ‘Window’ in networking terms?
Answer: Window is basically a method of controlling the flow of packets between two network hosts or computers. In a network, window “announcements” are sent by the receiving system to the transmitting system. It is a way of acknowledging data receipt to inform current buffer size to the transmitting system.
For instance, when a window size is reported as zero, transmitting systems should wait for an acknowledgment to send the next chunk of data. When the receiving system reports a larger buffer size as compared to a single data packet, the transmitting system can send multiple chunks of data before waiting for an acknowledgment.
Question #9. What are the two flags used in the core handshake of a typical TCP connection establishment?
Answer: The two flags used in the core handshake of a typical TCP connection establishment are SYN and ACK.
Question #10. What are the features of an IP access list?
Answer: There are three different kinds of access lists. These are standard, extended and named. Benefits of IP access lists include the following:
- Authenticate incoming rsh and rcp requests
- Block unwanted traffic or users
- Control access to vty
- Identify or classify traffic for QoS features
- Limit debug command output
- Provide bandwidth control
- Provide NAT control
- Reduce the chance of DoS attacks
- Restrict the content of routing updates
- Trigger dial-on-demand calls
Cisco interview questions for experienced candidates
The Cisco interview process for experienced candidates generally follows an established company pattern. All questions in this technical round are based on your CV. Typically, Cisco ASA interview questions are also asked during interviews conducted at Cisco systems India Pvt Ltd.
Below given are the Cisco interview questions experienced candidates may face in an interview.
Question #11. What is the access list range for extended IP, extended XNS, and extended VINES?
Answer: For Cisco devices, the extended IP access list range is 100 – 199 and 2000–2699.
The extended XNS access list range is 500–599.
The extended VINES access list range is 101–200.
Question #12. How will you use a linked list to simulate 3 TCP/IP packets?
Answer: In order to use a linked list to simulate 3 TCP/IP packets, all the packets should have a source IP, a destination IP, and some data (at least 20 characters).
Step 1: We need to search the packets one by one for suspicious IP (that starts with 000).
Step 2: We will then check the data for cipher, subtract 1 from ASCII of first 8 to see if “JOHN JAY” is the data.
Step 3: Our program should ideally simulate processing six packets in 2 groups of 3.
Step 4: Then we have to check all 3 packets (or nodes) and change the IP and data in each one and check again. Instead of a linked list, a QUEUE can be used, provided the QUEUE contains the same data.
Question #13. How is a TCP connection made?
Answer: A TCP connection is made as follows:
Step1: Sender and receiver synchronize so that a connection is made. The operating systems at both ends stay informed that a connection is established.
Step2: Then the sender starts transmitting data. It also gets acknowledgments. A timer is started as soon as the sender starts sending data.
Step3: If the sender has not received any acknowledgement even after the timer exceeds its limit, then it retransmits the data.
Step4: In case of windowing, if the buffer on the receiver is full, the receiver sends a stop signal to the sender. The sender stops transmitting data.
Step5: Then after processing all data, the receiver sends a go signal to the sender. Then, the sender starts transmitting data again. This is in case of windowing.
Question #14: What is a firewall and what is the security level in an ASA firewall?
Answer: Firewall is a layer or device placed between a trusted and an untrusted network. Its function is to deny or permit traffic access traveling into and out of the network. So, it is a protective layer that blocks unauthorized access by users on both sides of the firewall.
ASA Firewall Security Level can be 0-100. 100 is the highest security level on an ASA firewall and it represents the most trusted Zone. On the other hand, 0 is the lowest security level on an ASA Firewall.
Question #15: What is the Cisco default TCP session timeout?
Answer: TCP session timeout for Cisco is 1 minute. The connection slots are freed approximately 60 seconds after a normal connection close sequence. This can be configured to some other setting as per requirement. A global idle timeout duration can be set for the connection and translation slots of various protocols. If slots are not used for idle times specified, resources get returned in order to free pool.
Question #16: Which command enables failover in an ASA firewall?
Answer: The command is ‘Failover’.
Question #17: What is a transparent firewall?
Answer: A transparent firewall acts as a line of the layer between 2 devices. Transparent firewalls easily deploy existing networks. Transparent firewalls also let in layer 3 traffic from higher security levels to lower security levels without access lists.
Question #18: Which LAN switching method is used in Cisco Catalyst 5000?
Answer: Cisco Catalyst 5000 basically uses the store-and-forward switching method. The entire frame gets stored into buffers and a CRC check is performed before deciding whether or not the data frame should be forwarded.
Question #19: What are the different memories used in a Cisco router?
Answer: There are 3 types of memories used in a Cisco router namely:
NVRAM – to store the startup configuration file
DRAM – to store the configuration file which gets executed
Flash Memory – to store Cisco IOS.
Question #20: Explain how cut-through LAN switching works.
Answer: Cut-Through LAN switching can be explained like this. When the router receives a data frame, it immediately sends it out again and forwards the same to the next network, as soon as it reads the destination address.
HR round questions and answers for a Cisco interview process
Question #21: Any particular reason for leaving your current job?
Answer: I feel I am ready for a new stage and newer challenges in my career. I would like to continue growing as well as learn from my field. I have never been this confident about taking up more tasks and additional responsibilities. I don’t get too many complex opportunities to tackle in my current job role, especially related to protocols like OSPF, EIGRP, BGP and UDP. I am sure this role will surely present me with the opportunities to handle them.
Question #22: How would you explain an IP address to a layman?
Answer: Every machine connected to the Internet has a unique number assigned to it. This is an IP address. Without this unique number or tag on your machine, you will not be able to communicate with other users, computers and devices on the Internet.
In other words, IP address is like a telephone number, as it is unique and identifies a way to reach you exclusively. Hope I made myself clear.
Question #23. Why do you want to join this company?
Answer: Yours is a reputed organization and a global leader in high-end technology products and services. I truly admire this company’s rich value driven work culture. Besides, I am a huge fan of the present CEO. I came to know that he started his career as a software developer at a small firm. Moreover, the career graphs of your senior leadership team members are highly motivating. They signify that anyone ready to work hard and remain persistent, can easily grow in this organization.
Question #24. Did you apply for a position at some other company? Or What other companies are you interviewing with?
Answer: I believe I am still at a very early stage of job search. I’ve applied for a number of openings but this position particularly seems the most exciting to me. Honestly, your job description is a good fit for my skill sets and knowledge. Besides, I haven’t received a call from any other organization as good as this, yet.
Question #25. Do you have any prior experience as a network engineer?
Answer for a fresher: I completed my Bachelor’s degree only this year. Being a fresher, I do not have any prior professional experience related to Cisco and networking technologies. Still I would like to add that I was a Student Network Engineer in my college computer lab. I have also done 2 internships in this field and possess freelance experience as a backend developer. Also, I am in the process of completing my CCNA certification by next month.
Answer for an experienced applicant: I am a Microsoft Certified Solutions Expert with 2.5 years of relevant experience as a network engineer. I started my career as a help desk support officer. Due to lack of challenges on the job, I had to switch over to Cisco and networking. As of today, I am in love with what I do for a living as a networking engineer. Every single day brings forth newer opportunities to learn at work. From these challenges, I get to pick up the latest technology. I would like to add that I have completed both Cisco Certified Network Associate (CCNA) and Cisco Certified Network Professional (CCNP) certifications last year.
Hope you found our Cisco questions and answers useful. Start preparing with them for your Cisco interview and face your panel confidently.
Quick Tip: In order to add more weight to your resume, get a Cisco security certification done as soon as possible. Alternatively, you may consider a more generic online course in IT Hardware and Networking concepts to grow your knowledge.
Ultimately it is your job to help recruiters reach the right conclusion about your candidature! Completing the above-mentioned certifications in hardware and networking and preparing with the answers in this article, will help you answer all Cisco Interview Questions confidently. Thus, you will stand out as a strong potential candidate for the job.
All the best!