Staff Software Engineer – Low-Level Networking Agent

About Us
ZeroTier leads the world in next-generation connectivity and cybersecurity. Our platform provides highly secure, peer-to-peer virtual networks, relied upon by millions of users and businesses — from individual users and startups to mid-scale enterprises and Fortune 500 companies. We’re backed by awesome investors including Battery Ventures, Bonfire Ventures, and Anorak Ventures.

The Role
We are seeking a skilled Software Engineer to help build, extend, and maintain the ZeroTier client, the lightweight virtual networking engine that runs on millions of devices. This role blends networking, distributed systems, and systems-level engineering, focusing on secure, reliable, and high-performance connectivity.

You will contribute to the client’s networking stack, peer discovery, session management, and data-path performance, requiring strong knowledge of network protocols, OS internals, and low-level optimization. You’ll work closely with platform, infrastructure, and security teams to evolve a cross-platform codebase that runs consistently on Linux, Windows, macOS, mobile, and embedded environments.

Your work will shape how devices join virtual networks, discover peers, establish encrypted sessions, and communicate efficiently under real-world network conditions.

What You'll Do:
• Participate in design and implementation strategies to enhance and improve ZeroTier’s networking agent.
• Develop and maintain communication primitives using protocols such as TCP and UDP, as well as custom transport layers.
• Implement secure tunneling, NAT traversal techniques, and robust reconnection/keepalive mechanisms.
• Work with low level, OS-specific operations (sockets, netlink, firewall rules, etc.) to optimize data paths.
• Profile and optimize network performance (latency, throughput, connection reliability).
• Build cross-platform abstractions enabling the agent to run in varied environments.
• Write clean, maintainable, well-tested code and contribute to architecture documentation.
• Collaborate with cross-functional teams on system design, threat modeling, and deployment strategies.

What We're Looking For:
• Senior Level experience in network engineering or systems programming.
• Strong proficiency in C, C++ or Rust for low-level development.
• Deep understanding of:
• — Networking and protocols: OSI Model, IPv4/IPv6, IP routing, Ethernet
• — Internet routing, including IPAM, firewalls, NAT, multipath
• — NAT traversal techniques (STUN/TURN/ICE, hole punching)
• — Encryption standards and secure session establishment
• Experience with Linux and/or Windows networking internals and socket programming.
• Familiarity with overlay networks, VPN tunneling, mesh networking, or SD-WAN.
• Solid debugging and performance profiling skills using tools like tcpdump, Wireshark, perf, strace, etc.
• Ability to write technical documentation and communicate effectively with team members.
• Experience in a startup or fast-paced environment is a strong plus.

More About ZeroTier

Founded in 2013 by Adam Ierymenko, ZeroTier’s mission is to make peer-to-peer networking with strong encryption so simple, secure, and intuitive that it becomes the default for the internet.

To do this ZeroTier simplifies complex networking across physical boundaries, unifying cloud and edge environments. Our network virtualization platform offers enterprise-grade software-defined networking for every device, service, and applications, whether at the edge or in the cloud. It's powerful enough for large businesses and defense applications, yet easy for individuals to use for tasks like gaming or remote access.

Our team is the best of the best, working diligently to solve the hard technical challenges underlying high-performance decentralized networking. We help our customers run networks free of handcuffs and endless minutiae. Come join us!

To find out more please check us out at: www.zerotier.com

PLEASE NOTE: Individuals seeking employment at ZeroTier are considered without regard to race, color, religion, national origin, age, sex, marital status, ancestry, physical or mental disability, veteran status, or sexual orientation. Direct applicants ONLY. Any recruiter/3rd party submissions we receive will be considered a gift. Written CV’s and Cover Letters are encouraged. No calls please.