Arista Networks Coding Interview Questions: C, C++, Networking and Systems

Arista Networks, based in Santa Clara, makes data-center, cloud and campus switches and routers that run its EOS operating system. Its software interviews are unusually low-level: candidates consistently describe writing C by hand, linked lists, pointers and bit manipulation, sometimes in a plain terminal with vim and gdb. This page covers what Arista Networks builds and who it hires, the process candidates commonly report, the technical depth the teams care about, representative problem types, what interviewers score, and a three-week prep plan.

What Arista Networks builds and who it hires

Arista describes EOS as running on an unmodified Linux kernel, with each function in its own restartable process. These processes, called agents, do not talk to each other directly; they publish and subscribe to state in SysDB, an in-memory transactional state database, so an agent that restarts can pull its last known state. Engineers also build CloudVision, the network management platform, and the large test infrastructure behind EOS.

• EOS software engineers: agents for routing protocols, forwarding and management in C and C++.
• Platform engineers: bringing up new switch hardware and drivers.
• CloudVision engineers: network-wide state, telemetry and automation.
• Software and systems test engineers: test frameworks and network test beds, often in Python.

What the process tends to look like

Processes differ by team, level and office and change over time, so treat this as the common shape candidates report and confirm the specifics with your recruiter.

C, networking and operating systems

C by hand. Expect to write a linked-list deletion, reversal or merge from scratch, with struct definitions, malloc and free, and pointer-to-pointer techniques. Some candidates report working in vim and debugging with gdb, so practice outside an IDE. Our C programming interview questions cover the fundamentals.

Bits and bytes. Bit manipulation comes up often: counting set bits, checking powers of two, bit arrays for duplicate detection and packing fields into an integer. Know endianness and how a packet header maps onto a struct.

Networking and systems. Know Ethernet, IP and routing basics such as longest-prefix match, and the OS ideas EOS depends on: processes, shared memory, signals and what happens when a process crashes. Review our computer networks questions and operating system questions.

C or C++. One candidate reported a posting that said C++ and an interview in C, and another was screened on C++ syntax, so be fluent in both.

Representative problem types

These are the kinds of problems candidates describe, not a leaked question list. Practice the category, not the exact question.

1. Delete a node from a singly linked list using a pointer to the head pointer.
2. Reverse a linked list in place and merge two sorted lists.
3. Count set bits and detect duplicates with a bit array.
4. Implement longest-prefix match for IPv4 routes.
5. Parse an Ethernet or IP header from a byte buffer.
6. Traverse a binary tree without recursion.
7. Implement a fixed-size ring buffer for one producer and one consumer.

What interviewers score

• Correct C: code that compiles, frees what it allocates and handles empty lists, null pointers and boundary values.
• Understanding of the machine: what your code does to memory, the stack and the CPU, and why.
• Debugging discipline: how you find a fault with prints, assertions or a debugger instead of guessing.
• Clear reasoning about systems: explaining a networking, OS or hardware trade-off in plain words.

The behavioral side

Technical rounds decide most outcomes, but every Arista Networks loop also asks about how you work. Prepare a short story for each of these, with a result and what you learned:

• Something you shipped end to end. Cover the user problem, your decisions, what you measured and what you would change.
• A disagreement with a teammate. Show how you made the decision on evidence and kept the relationship.
• Why this company? Connect its product and engineering problems to the work you want to do next.

Structures and sample answers for the common questions are in our software engineer behavioral answers guide.

A three-week prep plan

1. Week 1: C by hand in a plain editor: linked lists (insert, delete, reverse, merge), a hash table with chaining and a ring buffer, each compiled with warnings on and run under a memory checker.
2. Week 2: bits and networking: ten bit-manipulation drills, parsing headers from byte buffers, longest-prefix match, and the computer networks questions basics of Ethernet, ARP, IP, TCP and routing.
3. Week 3: operating systems and debugging: processes, threads, signals and shared memory from our Linux interview questions, two gdb sessions on deliberately broken programs, and two mock interviews where you explain C code aloud.

For practice lists, use LeetCode company-tagged questions and the NeetCode 150 roadmap; for design rounds, read system design building blocks; and compare the practical style of Datadog.

Where CoPilot Interview fits

Most of a Arista Networks loop is spoken: you explain an approach, defend a trade-off and talk through your past work. CoPilot Interview is an AI interview assistant whose free AI mock interview builds technical and behavioral questions from your résumé and the job description, reads them aloud and scores each spoken answer out of ten, so you can rehearse the explanation as well as the code. The free plan gives 15 minutes a day of live help in sessions of up to 15 minutes, with AI mock interviews included. Online assessments and many coding rounds forbid outside help, so practice beforehand and follow your employer's rules on the day.

Disclosure: CoPilot Interview is our product, so weigh what we say about it accordingly.

Frequently asked questions

What programming language should I use in a Arista Networks interview?

C first, with C++ for some teams; test and tooling roles use Python. Expect to write code without IDE help.

Does Arista Networks send an online assessment?

Candidates mostly describe live technical phone screens rather than an online assessment; campus pipelines may differ. Confirm with your recruiter.

Will Arista interview me in C or C++?

Usually C, as candidates describe it, even for some postings that list C++, and some report C++ syntax questions too. Prepare both, and practice in a plain editor with a compiler and gdb rather than an IDE.

How should I prepare for Arista Networks coding questions?

Write C by hand every day for three weeks: linked lists, bit manipulation and buffers, compiled and debugged in a terminal rather than an IDE. Add networking basics such as IP routing and longest-prefix match, and operating-system concepts such as processes and shared memory, and explain every line aloud.

Can I use AI tools in a Arista Networks interview?

Only if the instructions you receive say so. Online assessments and live coding rounds generally forbid outside help, and some companies now state their AI policy in the invitation. Use AI to practice beforehand, and follow your employer's rules.