What is a Software Engineer?

A Software Engineer at Arista Networks builds the foundation that powers the world’s most demanding networks. You will develop features in Arista EOS (Extensible Operating System)—our Linux-based network operating system that runs across data center, routing, and campus platforms—and contribute directly to how packets are forwarded, routes are computed, interfaces are managed, and systems are tested at hyperscale.

This role has a uniquely high impact. Your code will be deployed in cloud providers, AI clusters, and large-scale enterprises, where performance, correctness, and reliability are non-negotiable. You will work in C/C++ and Python on Linux, implement and optimize L2/L3 features, collaborate with hardware teams on Layer1/PHY integration, and own projects end-to-end—from requirements and design through automated testing, release, and customer support.

What makes this role compelling is the combination of deep systems engineering, real protocol and device-level interactions (BGP, OSPF/IS-IS, EVPN/VXLAN, PHY/optics), and an engineering-driven culture that expects you to lead with technical rigor. If you want to build software that moves the internet and AI fabrics, this is where you do it.

Common Interview Questions

Use this interactive module on Dataford to practice questions by category, track progress, and benchmark against role expectations. Prioritize areas highlighted by your recruiter and tailor your drills to the specific team focus (e.g., Routing vs. Layer1 vs. Network Systems).

Getting Ready for Your Interviews

Your interviews will probe how you think, how you write software that works in production, and how you debug complex systems quickly. Expect a blend of coding in C/C++, core CS (data structures, OS, concurrency), and networking (L2/L3, TCP/IP, EVPN/VXLAN), along with discussions of design, testing, and ownership.

• Role-related Knowledge (Technical/Domain Skills)
  Interviewers assess depth in C/C++, Python for tooling, Linux, and networking protocols. You demonstrate this by writing correct, memory-safe, testable code; explaining OS and networking trade-offs; and showing familiarity with EOS-like systems (routing, packet forwarding, device drivers, telemetry).

• Problem-Solving Ability (How you approach challenges)
  You will be evaluated on decomposing ambiguous problems, selecting data structures/algorithms fit for scale, and balancing performance with maintainability. Think aloud, justify trade-offs, and show iterative validation (tests, assertions, logs).

• Leadership (How you influence and mobilize others)
  Arista expects engineers to “lead from the code.” Interviewers look for initiative, technical judgment, and end-to-end ownership: writing specs, building test plans, mentoring peers, and handling escalations with customers.

• Culture Fit (How you work with teams and navigate ambiguity)
  The bar includes honesty, clarity, and autonomy. Show that you can collaborate across software, hardware, test, and support; handle feedback; and operate with precision, pace, and quality in a small, high-output team.

Interview Process Overview

Arista’s interview experience emphasizes deep technical discussion with practicing engineers. You will notice strong alignment between questions and the actual work: writing C/C++ that runs on Linux, debugging complex interactions across protocols and hardware, and reasoning about performance and scale. The process is rigorous but respectful—interviewers aim to understand how you think under realistic constraints.

Expect efficient pacing. Some candidates see an initial coding assessment (e.g., a short, time-bound coding screen), while others move directly to live technical interviews. The philosophy is consistent: small teams, high agency, and a strong signal on quality. You will likely encounter coding, systems fundamentals (memory, threads, processes), networking (L2/L3, TCP/IP, EVPN/VXLAN), and a design/problem-solving conversation grounded in EOS-style components. Manager conversations focus on ownership, mentorship, and how you operate in production.

This timeline visualizes the typical progression from recruiter contact through technical screens, onsite/virtual panels, and decision. Use it to plan your prep cadence, block focused time for system design and coding practice, and prepare crisp examples for behavioral discussions. Keep momentum: confirm availability quickly, clarify expectations per round, and ask for any focus areas before each step.

Deep Dive into Evaluation Areas

Coding in C/C++ and Software Fundamentals

You will write C/C++ under realistic constraints: memory management, complexity targets, correctness, and testability. Expect to compile concepts you use daily—pointers/references, RAII, STL containers/iterators, time/space trade-offs—into clean implementations.

Be ready to go over:

• Core data structures/algorithms: arrays, strings, hash maps/sets, heaps, trees, graphs, sorting, searching
• C/C++ specifics: pointers, lifetimes, const-correctness, move semantics, smart pointers, exceptions vs. error codes
• Testing and correctness: unit tests, edge cases, invariants, input validation
• Advanced concepts (less common): lock-free structures, custom allocators, circular buffers, cache-aware designs

Example questions or scenarios:

• “Implement a rate limiter or LRU cache in C++ with O(1) operations and discuss thread-safety options.”
• “Parse a routing table dump into efficient in-memory structures; support longest-prefix match lookups.”
• “Given a packet header schema, encode/decode functions with robust bounds checking and tests.”

Systems: Linux, OS, Concurrency, and Performance

Arista software is systems software. You will be asked to reason about processes, threads, scheduling, memory, and I/O. Show that you can instrument code, analyze flame graphs or perf counters, and choose the right concurrency primitives.

Be ready to go over:

• Processes/threads: context switches, synchronization, deadlocks, condition variables, atomics
• Memory: stack vs heap, fragmentation, paging, NUMA basics, memory visibility
• I/O and performance: epoll/select, buffers, DMA basics, profiling
• Advanced concepts (less common): lock-free algorithms, memory barriers, copy-on-write, zero-copy I/O

Example questions or scenarios:

• “Design a multithreaded log aggregator; detail contention points and backpressure.”
• “Diagnose a memory leak or heisenbug in a long-running daemon; what tools and hypotheses?”
• “Compare polling vs. interrupt-driven I/O for a high-throughput task.”

Networking and Protocols (L2/L3, EVPN/VXLAN, TCP/IP)

You do not need to be a CCIE, but you should be comfortable with core concepts and data structures protocols rely on. Expect questions on packet paths, FIB/RIB, adjacency, timers, and failure handling at scale.

Be ready to go over:

• L2: VLANs, LACP, STP/RSTP/MST, MACsec basics
• L3 and routing: ARP/ND, OSPF/IS-IS, BGP, ECMP, convergence, route scaling
• DC fabrics: EVPN/VXLAN, MLAG, underlay/overlay, routing on the host
• Advanced concepts (less common): Segment Routing, telemetry/streaming, buffer management, QoS/PFC

Example questions or scenarios:

• “Explain EVPN route types and how MAC/IP mobility is handled.”
• “Design a control-plane approach to program 1M routes to a multi-ASIC chassis under tight time budgets.”
• “Trace a packet through an underlay/overlay fabric, pinpointing failure domains.”

System Design for Network Software (EOS-style Components)

Design interviews are grounded in real EOS problems: building a protocol module, a forwarding pipeline renderer, or a telemetry subsystem. Interviewers look for modularity, scale, observability, and failure handling.

Be ready to go over:

• APIs and abstractions: clean interfaces to hardware drivers and higher layers
• State and scale: in-memory models, snapshots, incremental updates, backpressure
• Resilience: process restarts, warm upgrades, hitless transitions, watchdogs
• Advanced concepts (less common): multi-ASIC partitioning, hardware offload orchestration, graceful in-service upgrades

Example questions or scenarios:

• “Design a BGP feature that supports fast failover and route dampening; outline data structures and timers.”
• “Build a packet forwarding state renderer for a router with hundreds of forwarding chips.”
• “Instrument a telemetry pipeline for link health and anomaly detection.”

Debugging, Testing, and Production Quality

Quality is a first-class deliverable. Expect to discuss how you write functional specs, test plans, and automated tests alongside the code. Be explicit about how you triage field issues and deliver confident fixes.

Be ready to go over:

• Test strategy: unit, integration, soak, fuzz; simulators and traffic generators
• Diagnostics and bring-up: board-level tests, link diagnostics, counters, PRBS
• Prod hygiene: feature flags, rollbacks, canaries, versioning
• Advanced concepts (less common): concurrency testing, determinism, fault injection

Example questions or scenarios:

• “Author a test plan for MACsec or LACP; include negative and scale cases.”
• “Given intermittent retransmissions at 400G, outline a methodical root-cause workflow.”
• “Design a diagnostic to validate a new PHY or optics module during manufacturing.”