---
title: Cisco Interview Questions & Preparation (2026 Guide)
description: A 2026 guide to the Cisco software and network engineer interview: the coding rounds, deep networking fundamentals, system design, and the behavioral round, plus how to prepare.
url: https://usegreenroom.app/blog/cisco-interview-questions
last_updated: 2026-06-20
---
← Back to blog
Companies
# Cisco interview questions and preparation
June 20, 2026 · 16 min read
Cisco is the networking company, and its interviews reflect that directly — alongside standard data structures and algorithms, you're expected to actually understand how networks work, not just recite the OSI model's layer names. Unlike an IT-services fresher-mill that mostly filters on aptitude and basic coding, Cisco is a product and infrastructure company: it builds the routers, switches, and software that run the internet's plumbing, and it hires people who can reason about that plumbing under questioning. This guide goes deep on what actually gets asked — the assessment, the networking content that differentiates Cisco from every other company on your list, the DSA and OS questions, the system design and behavioral rounds for experienced candidates, and a realistic way to prepare.
## The Cisco interview process
Cisco's pipeline varies by whether you're coming in as a fresher (campus hiring) or as an experienced engineer, but the shape is consistent: a screening assessment, two to four technical rounds, and a behavioral/HR round. Here's what each stage actually tests.
### What's on the online assessment?
The campus online assessment is usually split into three sections: quantitative aptitude (time-speed-distance, permutations/combinations, basic probability — nothing exotic, just fast and accurate), two coding problems on a judge, and a bank of technical MCQs. The coding problems are rarely exotic — expect something like "given an array, find the longest subarray with a sum equal to a target" (a sliding-window or prefix-sum problem) or a string manipulation problem like "check if two strings are anagrams ignoring case and spaces" — the kind of problem that rewards knowing the right pattern instantly rather than deriving it from scratch under time pressure. The technical MCQ section is the part candidates most underestimate: it draws from OSI/TCP-IP layers and their responsibilities, OOP pillars (encapsulation, inheritance, polymorphism, abstraction) with "what does this code print" style questions, and OS basics like process states, scheduling, and paging. Treat the MCQ section as seriously as the coding problems — a strong coding score with a weak MCQ score still gets filtered.
### How many technical rounds are there, and what do they cover?
Most candidates see two to three technical rounds. The first is typically DSA-focused — one or two problems on arrays, linked lists, trees, or graphs, solved live with the interviewer asking about time/space complexity and edge cases. The second is where Cisco diverges from a typical product company: a dedicated networking round that goes well past "name the OSI layers" into how protocols actually behave end to end. A third round (especially for roles touching IOS, network software, or systems-adjacent teams) often blends operating systems questions with a walk-through of a project you've built, probing what you actually understand about it versus what you copied from a tutorial.
## Cisco's networking questions, explained properly
This is the section that actually separates candidates at Cisco. Anyone can memorize "there are 7 OSI layers." Cisco interviewers ask follow-ups specifically designed to catch people who memorized labels without understanding what happens at each one.
### Explain the OSI model and what each of the 7 layers actually does.
The OSI model is a 7-layer conceptual framework for how data moves from one application to another across a network, and the layers matter because each one solves a distinct problem and hands off to the next. **Physical** (layer 1) moves raw bits over a medium — cables, radio, voltage. **Data Link** (layer 2) frames those bits and handles node-to-node delivery on the same network using MAC addresses — this is where switches operate. **Network** (layer 3) handles logical addressing and routing across different networks using IP addresses — this is where routers operate. **Transport** (layer 4) provides end-to-end communication with reliability guarantees (TCP) or speed (UDP), including segmentation and flow control. **Session** (layer 5) manages and maintains connections between applications. **Presentation** (layer 6) handles formatting, encryption, and compression so data is usable across systems. **Application** (layer 7) is where the actual user-facing protocols live — HTTP, FTP, SMTP. The follow-up Cisco interviewers always ask: "where does a switch operate, and where does a router operate?" — if you can't immediately answer layer 2 and layer 3 respectively, it signals you memorized the list without understanding the model's purpose.
### What's the difference between TCP and UDP, and when would you use each?
TCP is connection-oriented: it establishes a session via the three-way handshake (SYN, SYN-ACK, ACK), guarantees ordered and reliable delivery through acknowledgments and retransmission, and applies flow/congestion control to avoid overwhelming the receiver or the network. UDP is connectionless — it fires packets ("datagrams") with no handshake, no guaranteed order, and no retransmission, trading reliability for lower latency and overhead. You use TCP when correctness matters more than speed — web traffic, file transfer, email — and UDP when speed and low latency matter more than occasional packet loss being noticeable, like live video calls, online gaming, or DNS lookups. The interview signal: can you explain *why* the three-way handshake exists (both sides need to agree they can send and receive before committing resources to the connection), not just that it exists.
### What is subnetting, and why do networks use it?
Subnetting splits a larger IP network into smaller, logically separate sub-networks by borrowing bits from the host portion of an address to extend the network portion, expressed via a subnet mask or CIDR notation. The practical reasons: it reduces broadcast traffic (broadcasts stay within a subnet instead of flooding an entire organization), improves security by isolating segments from each other, and makes IP address allocation efficient instead of wasting an entire /24 block on a department that only needs 20 addresses. A typical interview probe is a small CIDR calculation:
10.0.0.0/24 has 256 addresses (254 usable hosts).
Splitting into /26 gives 4 subnets of 64 addresses each
(62 usable hosts per subnet, after network + broadcast).
Being able to do that arithmetic on the spot, even roughly, is a stronger signal than reciting the definition of subnetting.
### What is a routing protocol, and what's the difference between OSPF and BGP?
A routing protocol is how routers exchange information about network reachability so they can build routing tables and decide the best path for a packet, rather than relying on manually configured static routes that don't scale or adapt to failures. **OSPF** (Open Shortest Path First) is an interior gateway protocol used *within* a single organization's network — it builds a complete map of the network topology and computes shortest paths using a link-state algorithm, converging quickly when a link fails. **BGP** (Border Gateway Protocol) is the protocol that runs *between* autonomous systems — it's literally the protocol that holds the internet together, making routing decisions based on policy, path attributes, and business agreements between ISPs rather than pure shortest-path metrics. You don't need to configure either live in an interview, but you should be able to say which one operates inside a company's network versus between providers on the internet — that distinction is the actual point of the question.
### What is ARP, and why is it needed alongside IP addressing?
ARP (Address Resolution Protocol) resolves a known IP address to the corresponding MAC address on a local network, because IP operates at layer 3 with logical addresses while the actual delivery of a frame on the local segment happens at layer 2 using MAC addresses. When a device wants to send a packet to an IP address on its local network, it broadcasts an ARP request ("who has this IP?"), and the device owning that IP responds with its MAC address, which gets cached in the sender's ARP table to avoid repeating the broadcast for every packet. This question often comes paired with "what happens when you type a URL into a browser" — ARP is one of the steps people forget, right after DNS resolution and before the actual TCP handshake can happen on the local network.
### What is a VLAN, and why would you create one?
A VLAN (Virtual LAN) logically segments a single physical switch (or set of switches) into multiple separate broadcast domains, so devices in different VLANs can't see each other's broadcast traffic even though they're plugged into the same physical hardware. This matters for security (isolating finance traffic from guest WiFi on the same building's switches), for reducing broadcast noise on large networks, and for organizational flexibility (grouping users by department or function regardless of which physical port they're plugged into). Traffic between VLANs requires a router or a layer-3 switch to do inter-VLAN routing — a detail interviewers specifically check for, since it shows you understand VLANs don't eliminate the need for routing, they just change where the broadcast domain boundary sits.
### What's the difference between a switch, a router, and a hub?
A hub is a dumb layer-1 device — it repeats every incoming signal out every other port, with no awareness of addresses, which means every device shares the same collision domain and performance degrades as you add devices. A switch is a layer-2 device that learns which MAC address lives on which port and forwards frames only to the relevant port, giving each port its own collision domain and dramatically better performance and security than a hub. A router is a layer-3 device that connects separate networks and makes forwarding decisions based on IP addresses, using a routing table — it's the device that lets your home network talk to the wider internet, while your switch just connects devices within your own network. If an interviewer asks "could you replace a router with a switch," the answer is no for connecting distinct networks — a switch has no concept of IP routing.
### Walk me through what happens when you type a URL into a browser and press enter.
This is the canonical Cisco networking interview question, and it's really asking you to synthesize everything above into one coherent flow. First, the browser checks if it has the IP for the domain cached; if not, it performs DNS resolution, walking from the resolver up through root, TLD, and authoritative nameservers until it gets back an IP address. Then the device needs the destination's MAC address on the local network (ARP, or the gateway's MAC if the destination is remote) and establishes a TCP connection to the server via the three-way handshake, followed by a TLS handshake if it's HTTPS. The browser sends an HTTP request, the server processes it and sends back a response, and the browser parses the HTML, fetches any additional resources (CSS, JS, images) via additional requests, and renders the page. Interviewers grade this almost entirely on whether you can narrate it fluently and in the right order without prompting — it's a verbal fluency test disguised as a technical one.
## DSA, operating systems, and OOP — Cisco's standard technical layer
Networking depth is what differentiates Cisco, but it doesn't replace the standard technical bar — it's added on top of it.
### What data structure and algorithm topics actually come up?
Arrays and strings dominate the early rounds — two-pointer and sliding-window problems (subarray sums, longest substring without repeating characters), and sorting-adjacent problems. Linked lists show up specifically for reversal, cycle detection (Floyd's algorithm), and merge-style problems, partly because they map conceptually to how packets and queues are described in networking contexts. Trees and graphs appear in the slightly harder rounds — binary tree traversals, lowest common ancestor, and graph problems like BFS/DFS for connectivity or shortest path, which interviewers sometimes frame explicitly in network terms ("given this graph of routers and links, find the shortest path") to test whether you can connect DSA to the domain. None of this is unusually hard for a product company's bar, but Cisco does expect you to talk through complexity tradeoffs cleanly, not just produce a working solution.
### What operating systems concepts should I know?
Process versus thread is close to guaranteed: a process is an independent execution unit with its own memory space, while threads are lighter-weight units within a process that share the same memory space, which makes inter-thread communication cheap but introduces race conditions that inter-process communication doesn't have to worry about as directly. Deadlock comes up regularly — know the four necessary conditions (mutual exclusion, hold-and-wait, no preemption, circular wait) and at least one prevention or detection strategy, since "how would you prevent this" is the near-automatic follow-up. Memory management questions focus on paging versus segmentation, virtual memory's role in letting processes use more address space than physically exists, and what a page fault actually is. Process scheduling (round robin, priority scheduling, the tradeoffs between throughput and fairness) rounds out the list.
### What OOP concepts get tested, and how?
Expect the four pillars — encapsulation, inheritance, polymorphism, and abstraction — tested less by definition recall and more by "what does this code print" snippets that require you to trace through method overriding, constructor order in inheritance chains, or how an interface versus an abstract class changes what's enforced. Cisco interviewers also like asking you to justify a design choice in your own project: why you used inheritance versus composition somewhere, which tests whether you understand the tradeoff (composition is generally more flexible and avoids tight coupling) rather than just having used whichever pattern a tutorial showed you.
Cisco is a networking company — expect serious networking and systems depth.
## Cisco system design and behavioral rounds (experienced candidates)
### What does a Cisco system design round actually look like?
For experienced roles, the design round is often network-flavored rather than a pure web-scale system design question — think "design a rate limiter," "design a load balancer," or a hybrid like "design a system to monitor link health across thousands of network devices and alert on failures." The evaluation criteria are the same as any design round — clarify requirements, define scale and constraints, propose a high-level architecture, then go deep on one or two components — but Cisco interviewers specifically reward candidates who bring networking primitives into the answer naturally: discussing heartbeat/keepalive mechanisms, how you'd handle partial network partitions, or why you'd choose UDP for a lightweight health-check ping versus TCP for the control plane that needs reliability. A candidate who treats this as a generic "design Twitter" exercise without touching networking realities is missing the point of the round.
### What behavioral questions come up, and how should I structure answers?
The standard trio is a hard technical problem you solved (pick something with real technical depth — a bug that took real debugging, not a feature you shipped on schedule), a conflict with a teammate (show how you resolved it through communication, not who was "right"), and working under ambiguity (a project where requirements were unclear or changing, and how you made progress anyway). Structure every answer in STAR — Situation, Task, Action, Result — and be specific: name the actual system, the actual disagreement, the actual metric that improved. Vague answers ("we had a conflict and we talked it out and it worked fine") read as unprepared; specific ones read as someone who can actually recall and reason about their own work under questioning.
## What separates strong candidates from rejected ones
The strongest Cisco candidates have networking fluency that goes past memorized terminology — they can explain *why* TCP needs a three-way handshake, *why* a switch and a router operate at different layers, and *why* BGP exists separately from OSPF, not just list the terms. The most common rejection reason isn't failing a coding problem; it's giving shallow networking answers that fall apart under a single follow-up question — naming the seven OSI layers correctly but being unable to say what actually happens at each one, or describing TCP and UDP as "TCP is reliable, UDP is fast" without being able to explain the mechanism that makes TCP reliable. A close second is weak operating systems fundamentals — not knowing the difference between a process and a thread, or being unable to name a single deadlock condition. Cisco interviewers have heard the memorized version of every networking answer; what gets you through is being able to handle a follow-up that requires actually understanding the mechanism, not just the vocabulary.
The core truth: Cisco rewards networking depth. The candidate who can explain TCP, routing, and the OSI model cleanly under follow-up questions — and connect them to real systems — stands out instantly here, far more than someone who simply solved more LeetCode problems.
## A realistic prep plan
Give yourself two to three weeks if you're starting from a reasonable DSA baseline. Week one: rebuild your networking fundamentals from scratch, not from memory — go layer by layer through OSI, work through TCP vs UDP and the handshake, practice subnetting calculations until they're fast, and rehearse the "what happens when you type a URL" walkthrough out loud until it's fluent without notes. Week two: split time between DSA practice (arrays, linked lists, trees, graphs — focus on explaining your approach out loud, not just getting to a working solution) and operating systems fundamentals (process/thread, deadlock, memory management). In the final days, do full mock rounds that mix a coding problem with networking follow-ups, since that's exactly how Cisco's actual technical rounds are structured, and if you're targeting an experienced role, rehearse two or three STAR stories until you can tell them without rambling.
## How to prepare for the verbal part
Networking rounds are entirely verbal — you're not writing code, you're explaining protocols, flows, and tradeoffs while someone listens for gaps in your reasoning. Practise narrating things out loud, especially "what happens when you type a URL," subnetting math, and the OSI layer breakdown, because reading an explanation silently and producing it fluently under questioning are different skills. [Greenroom](/) runs spoken technical mock interviews that ask realistic follow-up questions on your networking and systems answers, the same way a real Cisco interviewer would. Pair it with our [networks](/blog/computer-networks-interview-questions) and [OS](/blog/operating-system-interview-questions) guides for the underlying content, and [behavioral STAR answers](/blog/behavioral-star-answers-senior-engineers) if you're prepping for an experienced-candidate loop.
## Frequently asked questions
### What does Cisco focus on in interviews?
Cisco leans heavily on computer networks fundamentals — the OSI model, TCP vs UDP, subnetting, routing protocols, ARP, and VLANs — alongside standard data structures and algorithms, especially for network and systems roles. Strong, clearly explained networking knowledge that survives follow-up questions is a genuine differentiator at Cisco that it isn't at most product companies.
### What is the Cisco interview process?
Cisco's process typically includes an online assessment for campus hiring (aptitude, two coding problems, and technical MCQs on networking, OOP, and OS), two to three technical rounds covering data structures, computer networks, operating systems, and your project, and a behavioral or HR round on fit and communication. Experienced roles add a system design round that's often network- or systems-flavored.
### What networking questions does Cisco ask most often?
The most common are explaining the OSI model layer by layer, TCP versus UDP and why the three-way handshake exists, subnetting and basic CIDR math, the difference between a switch, router, and hub, what ARP and VLANs do, and the classic "what happens when you type a URL into a browser" walkthrough that ties everything together.
### What coding questions does Cisco ask?
Cisco asks standard data-structure and algorithm questions on arrays, linked lists, trees, and graphs — often sliding-window or two-pointer array problems and traversal-based tree/graph problems — along with OOP questions and a project deep dive. These are paired with substantial computer networks and operating systems questions, which is what sets Cisco's technical rounds apart from a typical product company.
### What's the most common reason candidates get rejected at Cisco?
Shallow networking answers that fall apart under one follow-up question — being able to name the OSI layers but not explain what actually happens at each one, or saying "TCP is reliable" without being able to explain the three-way handshake or retransmission mechanism that makes it reliable. Weak operating systems fundamentals, like not knowing the difference between a process and a thread, is a close second.
### How should I prepare for a Cisco interview?
Prioritize rebuilding real networking fundamentals over memorizing definitions — subnetting math, the OSI model layer by layer, TCP vs UDP mechanics, and the "what happens when you type a URL" walkthrough — alongside standard DSA and operating systems prep. Practise explaining protocols and flows out loud, ideally with a voice-based mock interview that asks follow-ups, because Cisco's networking rounds are entirely verbal and reward fluency under questioning, not just correct answers.
Cisco rewards networking depth explained cleanly under real follow-up questions. Greenroom runs spoken technical interviews that follow up on your reasoning. Free to start.