Senior Software Engineer — Embedded C / Firewall Client

SonicWall; Maharashtra; On-site; INR 300,000 - 600,000; Full time

Job summary

SonicWall is seeking a Senior Software Engineer to develop and maintain the Content Filtering Service client embedded in SonicOS, the firmware powering SonicWall firewall appliances. The role focuses on a C codebase with a split Control Plane / Data Plane architecture and requires deep knowledge of kernel networking, IPv4/IPv6, and robust firmware upgrade paths.

The ideal candidate will own the UDP protocol between the firewall and rating servers, collaborate with teams in the US and India, and

Qualifications

• At least 8 years of related experience with a Bachelor's degree; or 6 years with a Master's degree; or a PhD with 3 years' experience.
• Degree in Computer Science, Engineering, or related field preferred.
• Expert-level C with disciplined memory management and systems design.
• Kernel-level networking and TCP/UDP processing across a firewall dataplane.
• Strong IPv4/IPv6 support across all code paths.
• Experience navigating a large C codebase with multiple subsystems.
• Experience with network testing tools: Wireshark/tcpdump and GDB.

Responsibilities

• Maintain, harden, and extend the CFS client module across control and data planes.
• Own the binary UDP protocol implementation between firewall and rating servers.
• Develop and maintain IPv4/IPv6 support across all code paths.
• Manage firmware upgrade/migration paths ensuring atomic transitions.
• Improve inter‑blade cache synchronization on multi‑blade appliances.
• Collaborate with US‑based and India‑based teams on protocol changes.
• Document concurrency model, upgrade invariants, and dataplane integration.

Skills

C programming

Kernel networking

IPv4/IPv6

Concurrency (multicore)

GDB

Wireshark/tcpdump

Education

Bachelors in CS/Engineering

Master's degree

PhD (optional)

Tools

Wireshark

tcpdump

Job description

SonicWall is a cybersecurity forerunner with more than 30 years of expertise and is recognized as a leading partner‑first company, ensuring our partners and their customers are never alone in the fight against cybercrime. With the ability to build, scale and manage security across the cloud, hybrid and traditional environments in real‑time, SonicWall provides relentless security against the most evasive cyberattacks across endless exposure points for increasingly remote, mobile and cloud‑enabled users. With its own threat research centre, SonicWall can quickly and economically provide purpose‑built security solutions to enable any organization—enterprise, government agencies and SMBs—around the world. For more information, visit www.sonicwall.com or follow us on Twitter, LinkedIn, Facebook and Instagram.

About the Role

SonicWall is hiring a Senior Software Engineer to develop and maintain the Content Filtering Service client embedded in SonicOS—the firmware running on SonicWall firewall appliances worldwide. This module intercepts live traffic, queries the CFS rating servers in real time, and enforces URL‑based content filtering policies at the packet level. This is security‑critical code: a policy bug is a traffic bypass on a deployed security appliance.

The codebase is in C with a split Control Plane / Data Plane architecture, multi‑blade cache synchronization, and multiple firmware version upgrade paths.

Responsibilities

• Maintain, harden, and extend the CFS client module across both the control plane and data plane.
• Own the binary UDP protocol implementation between the firewall and the CFS rating servers, ensuring correctness and compatibility across protocol versions.
• Develop and maintain complete IPv4 and IPv6 support across all code paths.
• Own the firmware upgrade and migration paths, ensuring they are atomic, failure‑safe, and correctly handle all supported version transitions.
• Improve reliability of inter‑blade cache synchronization on multi‑blade appliances.
• Collaborate with the server‑side on coordinated protocol changes.
• Document the concurrency model, upgrade invariants, and dataplane integration for long‑term maintainability.
• Collaborate asynchronously with a US‑based team and the India‑based server team.

Requirements

• Expert‑level C (not C++): disciplined manual memory management, pointer arithmetic, and systems design.
• Multi‑core concurrency in C: reader‑writer locks, spinlocks, atomic operations, and memory ordering.
• Kernel‑level networking: deep understanding of how a packet moves through a firewall dataplane—TCP/UDP processing, flow cache, connection tracking. Userspace socket programming alone is not sufficient.
• Strong IPv4 and IPv6 across all code paths.
• Comfortable navigating and owning a large C codebase with multiple subsystems.
• Experience with network testing and debugging tools: packet capture (Wireshark/tcpdump), traffic generators, GDB.

Nice to have

• Experience with multi‑blade or multi‑ASIC hardware platforms (Octeon/CVMX or similar).
• Understanding of symmetric encryption (AES‑CBC, DES) at the C implementation level.
• Prior experience on a security appliance, network device, or UTM firmware codebase.
• Familiarity with TLV binary protocol design and versioning.
• Experience with C fuzz testing or sanitizers (AFL, AddressSanitizer, ThreadSanitizer).

Education & Experience

At least 8 years of related experience with a Bachelor's degree; or 6 years with a Master's degree; or a PhD with 3 years' experience; or equivalent experience preferred. Degree in Computer Science, Engineering, or related field preferred.

Equal Opportunity

SonicWall is an equal opportunity employer.

We are committed to creating a diverse environment and are an equal opportunity employer. All qualified applicants receive consideration for employment without regard to race, color, ethnicity, religion, sex, gender, gender identity and expression, sexual orientation, national origin, disability, age, marital status, veteran status, pregnancy, or any other basis prohibited by applicable law.

At SonicWall, we pride ourselves on recruiting a diverse mix of talented people and providing active security solutions in 100+ countries.