# Cisco Interview Source: https://www.techinterview.org/companies/cisco-interview/ Updated: 2026-07-12 · techinterview.org **TL;DR —** The Cisco interview process usually runs through a recruiter screen, an online or phone technical assessment, and a final loop of coding, technical, and behavioral rounds. Coding questions center on data structures and algorithms — arrays, strings, trees, and graphs — while role-specific interviews add depth on networking, protocols, and system design. Behavioral rounds assess teamwork and fit with Cisco's collaborative culture, so prepare examples in a structured format like STAR. ## Cisco Interview Process: Complete 2026 Guide Interviewed at Cisco in 2021 for a network software engineer role. Got the offer but went with a different company. The process was thorough but not overwhelming - here's what to expect. ### Overview Cisco is networking infrastructure at massive scale. They invented much of the internet as we know it. The interview reflects their focus: strong fundamentals, systems thinking, and real-world problem-solving over algorithmic tricks. Don't expect leetcode hard questions. Expect deep technical discussions about networks, protocols, and building reliable systems. ### Interview Structure **Phone Screen (45 minutes):** - 1 coding problem ([medium difficulty](/problems-by-difficulty/)) - Discussion of networking concepts - Questions about your background - Why Cisco? My phone screen: Implement a simple routing algorithm, then discuss TCP vs UDP tradeoffs. **Onsite (4-5 hours, can be virtual):** - 2 coding rounds (45 min each) - 1 [system design](/category/system-design/) round (60 min) - 1 networking deep dive (45 min) - 1 [behavioral round](/post/3233460379/behavioral-interview-questions-2026-star-method-amazon-leadership-principles-and-winning-answers/) (30 min) ### Technical Focus Areas **1. Networking Knowledge (Critical)** This is Cisco - they WILL test networking: - OSI model (all 7 layers) - be able to name each layer and give a concrete example of what lives there, like Ethernet at L2, IP at L3, and TCP at L4. Interviewers often point at a technology and ask which layer it belongs to. - TCP/IP protocols - know the three-way handshake, how TCP guarantees ordered delivery, and why UDP drops that guarantee for speed. Expect a follow-up on when you'd pick one over the other. - Routing algorithms (OSPF, BGP) - understand that OSPF is a link-state protocol used inside a single network and BGP exchanges routes between autonomous systems across the internet. Be ready to explain how each one selects a path. - Network security - cover firewalls, ACLs, TLS, and common attacks like DDoS and man-in-the-middle. A likely prompt is how you'd secure traffic between two data centers. - Load balancing - explain L4 vs L7 balancing, round-robin vs least-connections, and how health checks pull a dead backend out of rotation. - DNS, CDN concepts - walk through how a DNS query resolves a name to an IP, including caching and TTLs, and how a CDN uses edge caching plus geographic routing to serve content closer to users. Know your networking fundamentals cold. **2. Data Structures & Algorithms (Moderate)** Medium leetcode level: - [Graphs](/problems-by-topic/) (very important for routing) - networks are graphs, so know adjacency lists, BFS/DFS, and shortest-path algorithms cold. This is the single most likely topic to come up in a coding round here. - Trees (prefix trees for routing tables) - a trie is how routers do longest-prefix matching on IP addresses, so be able to build one and search it. Expect to explain why a trie beats a flat lookup table for this. - Hash tables - the default for O(1) lookups like mapping a MAC address to a port. Be ready to talk through collision handling and when hashing degrades. - Queues (for packet processing) - packets get buffered in queues, so know FIFO behavior and how a bounded queue handles overflow, whether you drop packets or apply backpressure. - Some string manipulation - parsing addresses, protocol headers, and config strings shows up, so be comfortable with splitting, matching, and basic pattern work. Focus on graph algorithms - shortest path, traversal, etc. **3. System Design (Network Focus)** Expect network-related design questions: - Design a load balancer - discuss how requests get distributed across backends, how you track backend health, and how you keep the balancer itself from being a single point of failure. - Design a CDN - cover edge server placement, cache-hit ratio, what happens on a miss (the origin fetch), and how you invalidate stale content. - Design a distributed firewall - think about where the rules live, how you keep policy consistent across many nodes, and how you filter traffic without adding noticeable latency. - Design a monitoring system for network devices - talk through polling vs push (SNMP vs streaming telemetry), where you store the time-series data, and how alerts fire when a metric crosses a threshold. **4. C/C++/Python Skills** Cisco uses low-level languages for performance: - C/C++ for systems programming - expect pointer work, manual memory handling, and questions about why low-level control matters when you're moving packets at line rate. - Python for automation and tooling - used for scripting device config, test harnesses, and network automation, so be fluent with the standard library and quick to prototype. - Understanding of memory management - know stack vs heap, what causes leaks, and how you'd track down a use-after-free or buffer overflow in C. - Performance optimization - be ready to profile before optimizing and to discuss cache locality, lock contention, and avoiding unnecessary copies on hot paths. ### Coding Interview Tips **Round 1 - Algorithms:** Problem I got: "Given a network topology as a graph, find the shortest path between two routers considering link costs." This is Dijkstra's algorithm. They wanted: - Working implementation - write code that actually runs, not pseudocode; they want to see you get the graph representation and the priority queue right. - Handling of edge cases (disconnected nodes, negative weights) - Dijkstra breaks on negative weights, so call that out, and know that a disconnected node simply means no path exists. - [Time/space complexity](/big-o-cheat-sheet/) analysis - state the big-O of your approach; Dijkstra with a binary heap is O((V + E) log V), and be ready to justify where that comes from. - Discussion of when to use Dijkstra vs Bellman-Ford - Dijkstra is faster but assumes non-negative weights; Bellman-Ford handles negative edges and can detect negative cycles. **Round 2 - Implementation:** Problem: "Implement a [rate limiter](/post/3233474159/system-design-rate-limiter-token-bucket-sliding-window-leaky-bucket-distributed-rate-limiting-api-gateway/) for network traffic." Required: - Token bucket or leaky bucket algorithm - know the difference: a token bucket allows bursts up to the bucket size, while a leaky bucket smooths output to a fixed rate. - Thread safety considerations - the limiter is shared across threads, so protect the counter with a lock or an atomic, and mention the contention tradeoff. - Performance optimization - this sits on a hot path, so keep the per-request work minimal and avoid locking on every call where you can. - Testing approach - cover the steady-state rate, bursts, and the boundary where requests start getting rejected, plus how you'd test concurrent access. ### System Design Interview Question: "Design a globally distributed CDN." Cover: - **Architecture:** Edge servers, origin servers, routing - **Caching:** What to cache, eviction policies - **Routing:** How to route users to nearest edge - **Consistency:** Cache invalidation strategies - **Monitoring:** Health checks, metrics They care about practical details - "How do you handle a datacenter outage? How do you update cached content?" ### Networking Deep Dive This round was unique to Cisco. Expect detailed technical questions: - "Explain how TCP congestion control works." - "What happens when you type a URL in a browser?" (network perspective) - "How does BGP routing work?" - "Explain the difference between L2 and L3 switching." - "How would you troubleshoot packet loss?" Be ready to go deep. If you say you know something, they'll test you on it. ### Behavioral Interview Cisco values: - **Collaboration:** Working across teams - **Innovation:** New approaches to problems - **Customer focus:** Enterprise customers matter - **Integrity:** Doing the right thing Questions: - "Tell me about a time you debugged a complex systems issue." - "How do you handle disagreements with team members?" - "Describe a project where you had to learn new technology." ### Preparation Strategy **Networking (2-3 weeks):** - Review OSI model thoroughly - Understand TCP/IP stack - Study routing protocols - Practice explaining concepts simply **Coding (3-4 weeks):** - 50-75 leetcode medium problems - Focus heavily on graphs - Practice in C++ or Python - Emphasize clean, efficient code **System Design (2 weeks):** - Study CDN architectures - Learn about load balancers - Understand distributed systems basics - Focus on reliability and scale ### Difficulty: 6.5/10 Easier than FAANG (7-9/10) but requires strong networking knowledge that many software engineers lack. If you have a strong networking background, it's manageable. If you're pure software with weak networking, prepare thoroughly. ### Compensation (2024 data) - **New grad:** $110-130K base + $15-30K stock - **Mid-level:** $130-160K base + $30-60K stock - **Senior:** $160-220K base + $60-120K stock - **Staff+:** $220-300K+ [total comp](/total-comp-calculator/) Lower than FAANG but very good work-life balance. Bonus is 10-15% of base. ### Culture & Work-Life Balance **Pros:** - Excellent work-life balance (40 hours/week) - Stable, mature company - Working on critical infrastructure - Good benefits and perks - Remote options available **Cons:** - Slower pace than startups - Some bureaucracy - Less exciting tech for pure software folks - Compensation below FAANG ### My Experience Coding rounds went well - I had practiced graph algorithms specifically for Cisco. Networking deep dive was tough but I had studied. Got the offer but went with a higher-paying opportunity. If I had taken it, would've been a solid choice for someone who wants work-life balance and enjoys networking. ### Final Tips - **Study networking deeply:** This is non-negotiable - **Practice graph algorithms:** Come up frequently - **Think about scale and reliability:** Network infrastructure must always work - **Show passion for networking:** They want people who care about packets - **Ask about the product:** Cisco has many divisions - know which one Cisco is great if you want to work on fundamental internet infrastructure with good work-life balance. Not flashy, but solid and stable.