Core Concepts:
- Process management (fork, exec, threads, signals)
- Inter-process communication (pipes, shared memory, message queues, sockets)
- Memory management (virtual memory, page tables, malloc internals)
- File systems (VFS, inode, dentry cache, file descriptors)
- Network stack internals (Netfilter, iptables, routing tables, FIB/RIB)
- System calls vs library calls
- Context switching and scheduling
- epoll/select/poll for high-performance I/O
Command Line Mastery:
- Debugging: strace, ltrace, gdb, valgrind
- Performance: perf, top, vmstat, iostat, netstat, ss
- Network tools: tcpdump, wireshark, ip, ethtool
- System inspection: /proc, /sys filesystem
Advanced Topics:
- Kernel modules and device drivers
- eBPF and XDP for packet processing
- Linux network namespaces and containers
- DPDK (Data Plane Development Kit)
- Zero-copy networking
Sample Interview Questions :
- How would you debug a memory leak in a production routing daemon?
- Explain the journey of a packet from NIC to application
- How does Linux kernel routing table lookup work?
- What's the difference between soft and hard IRQs in network processing?
Essential Data Structures:
- Hash Tables: Routing table lookups, neighbor tables
- Tries: Longest prefix matching in routing
- Trees: RB-trees for timers, B-trees for databases
- Graphs: Network topology, shortest path algorithms
- Heaps: Priority queues for event scheduling
- Bloom Filters: Fast membership testing
- LRU/LFU Caches: Route cache implementations
Critical Algorithms:
- Dijkstra's algorithm (OSPF SPF calculation)
- Bellman-Ford (Distance vector protocols)
- Tree algorithms (Spanning tree, minimum spanning tree)
- Graph traversal (DFS, BFS for topology discovery)
- Sorting and searching optimizations
- String matching (ACL/policy matching)
Sample Coding Questions :
1. Implement longest prefix match (LPM) algorithm
2. Design a routing table with fast insertion and lookup
3. Implement Dijkstra with priority queue optimization
4. Design an efficient neighbor discovery mechanism
5. Implement rate limiting using token bucket algorithm
6. Design a timer wheel for protocol timers
7. Implement a lock-free queue for packet processing
8. Design a memory pool allocator for protocol messages
Space/Time Complexity:
- Master Big O notation for all common operations
- Understand trade-offs in your protocol implementations
- Be ready to analyze your past work's complexity
Deep Dive Topics:
- LSA types and flooding mechanism
- SPF calculation optimization (incremental SPF)
- Area design and stub areas
- Virtual links implementation
- Graceful restart mechanisms
- Fast convergence techniques (LFA, RLFA)
- Multi-area adjacency
- OSPFv3 differences (IPv6 considerations)
Sample Design Questions:
- How would you optimize OSPF for a large-scale network (10,000+ routers)?
- Explain your LSA database implementation strategy
- How do you handle SPF calculation without blocking other operations?
- Design a test framework for OSPF implementation
- BGP state machine and optimization
- Route selection algorithm (13 steps)
- Policy implementation (import/export filters)
- BGP attributes and manipulation
- Route reflection and confederation design
- Graceful restart and NSR
- BGP convergence optimization
- ADD-PATH implementation
- Label distribution mechanisms
- LDP neighbor discovery and session management
- FEC-to-label binding
- Label stack operations
- PHP (Penultimate Hop Popping)
- MPLS-TE and RSVP-TE
- Segment Routing vs traditional MPLS
- IGMP snooping implementation
- PIM-SM vs PIM-DM trade-offs
- RPF check implementation
- Multicast routing table management
- SSM (Source-Specific Multicast)
- Multicast VPN considerations
- IP address allocation algorithms
- DHCP relay agent implementation
- Lease management and database design
- High availability for DHCP
- IPv6 address management (DHCPv6, SLAAC)
Sample Cross-Protocol Questions:
- How do you ensure protocol interactions don't cause issues?
- Design a unified routing table for all protocols
- Explain inter-protocol route redistribution
- How do you handle protocol priority and route preference?
Network Software Architecture:
- Modular design patterns for protocol stacks
- Event-driven vs multi-threaded architectures
- State machines for protocol implementation
- Separation of control and data planes
- High availability and redundancy design
- Scalability patterns (horizontal and vertical)
- Microservices architecture for network functions
Performance Optimization:
- Lock-free data structures
- Cache optimization techniques
- Batch processing for packets
- Interrupt handling and NAPI
- Busy polling vs interrupt-driven I/O
- NUMA awareness
- CPU affinity and thread pinning
High Availability:
- Stateful vs stateless failover
- Non-Stop Routing (NSR)
- Graceful Restart (GR)
- In-Service Software Upgrade (ISSU)
- Split-brain prevention
- State synchronization mechanisms
- Hitless upgrades
Sample Design Questions:
1. Design a high-performance routing daemon supporting 1M routes
2. Architecture for a distributed routing control plane
3. Design a protocol stack for multi-vendor interoperability
4. System design for network telemetry and monitoring
5. Design a testing framework for protocol validation
6. Architecture for SDN controller
7. Design configuration management for network devices
Systematic Debugging Approach:
- Protocol state analysis
- Packet capture and analysis
- Log analysis and correlation
- Performance profiling
- Memory leak detection
- Deadlock and race condition detection
- Core dump analysis
Tools Expertise:
- tcpdump/wireshark filter expressions
- gdb for multithreaded debugging
- Valgrind for memory issues
- perf for performance analysis
- SystemTap/eBPF for dynamic tracing
Sample Scenario-Based Questions:
1. OSPF neighbors stuck in EXSTART - how do you debug?
2. BGP session flapping - troubleshooting steps?
3. Memory leak in production - how to identify and fix?
4. High CPU usage in routing daemon - investigation approach?
5. Packets being dropped - where and why?
6. Protocol convergence taking too long - optimization strategy?
Core Concepts:
- Thread synchronization (mutexes, spinlocks, semaphores)
- Lock-free and wait-free algorithms
- Read-Write locks for routing tables
- Atomic operations and memory barriers
- Thread pools and work queues
- Producer-consumer patterns
- Thread-safe data structures
Race Conditions & Deadlocks:
- Detection techniques
- Prevention strategies
- Lock ordering
- Deadlock recovery
Real-World Applications:
- How do you protect routing table during updates?
- Multi-threaded packet processing design
- Thread-safe logging mechanisms
- Concurrent timer management
Packet Processing:
- Zero-copy techniques
- Batch processing
- Prefetching and cache optimization
- SIMD instructions for packet processing
- Kernel bypass techniques (DPDK, XDP)
Routing Performance:
- Fast path vs slow path separation
- Hardware acceleration
- Route aggregation
- FIB compression techniques
Metrics to Know:
- Packets per second (PPS)
- Latency (p50, p95, p99)
- CPU utilization per core
- Memory bandwidth
- Cache hit rates
Testing Strategies:
- Unit testing for protocols
- Integration testing across protocols
- Conformance testing (RFC compliance)
- Interoperability testing
- Performance testing and benchmarking
- Chaos engineering for network failures
- Fuzzing for security
Test Automation:
- Continuous integration for protocol code
- Automated regression testing
- Virtual network topologies for testing
- Emulation vs simulation trade-offs
Code Quality:
- Code review best practices
- Static analysis tools (Coverity, cppcheck)
- Memory sanitizers
- Code coverage metrics
Expect questions on:
- How do you make technology choices?
- Trade-off analysis frameworks
- Technical debt management
- Scalability vs complexity balance
- Build vs buy decisions
- Open source integration strategies
- Future-proofing designs
Past Project Deep Dives:
- Why did you choose specific implementations?
- What would you do differently now?
- How did you handle technical challenges?
- Performance bottlenecks and solutions
- Lessons learned from failures
Expect coding rounds on:
Easy-Medium:
- Implement LRU cache for routing entries
- Parse BGP update message
- Validate IP address and subnet
- Implement rate limiter (token bucket)
- Design a simple packet parser
- Implement prefix tree for IP routing
Medium-Hard:
- Implement Dijkstra's algorithm efficiently
- Design routing table with LPM
- Implement timer wheel
- Thread-safe queue implementation
- Design packet buffer management
- Implement sliding window protocol
System Design:
- Design a distributed routing protocol
- Architecture for network monitoring system
- Design BGP route server
- High-availability routing daemon design
Stay current with:
-
SDN (Software-Defined Networking)
- OpenFlow, P4 programming
- Network disaggregation
-
NFV (Network Functions Virtualization)
- VNF lifecycle management
- Service chaining
-
Cloud Networking
- VPC and overlay networks
- Container networking (CNI)
- Kubernetes networking
-
Network Automation
- NETCONF, YANG models
- gRPC and Protocol Buffers
- Streaming telemetry
-
Segment Routing
- SR-MPLS, SRv6
- Traffic engineering applications
-
5G and Edge Computing
- Network slicing
- MEC (Multi-access Edge Computing)
Network Security:
- Protocol security (authentication, encryption)
- DoS/DDoS mitigation in protocols
- Secure coding practices
- Input validation and sanitization
- Buffer overflow prevention
- Time-of-check-time-of-use issues
Authentication & Authorization:
- MD5, SHA authentication in protocols
- Key management
- Certificate-based authentication
- AAA integration (RADIUS, TACACS+)
Technical Leadership:
- Mentoring junior engineers
- Code review approach
- Driving technical decisions
- Influencing without authority
- Cross-team collaboration
- Handling disagreements
Project Examples (Use STAR method):
Situation: Context and challenge
Task: Your responsibility
Action: What you did
Result: Outcome and impact
Prepare 5-7 stories covering:
- Most complex technical problem solved
- Failed project and lessons learned
- Conflict resolution with team/stakeholders
- Innovation you drove
- Performance optimization achievement
- Mentoring success story
- Tough technical decision and rationale
Research the company:
- Products and technology stack
- Engineering blog posts
- Open source contributions
- Technical challenges they face
- Their network architecture
- Recent news and direction
Prepare questions for them:
- Technical challenges in their networking stack
- Team structure and collaboration model
- Technology choices and rationale
- Performance requirements and scale
- Development processes and tools
- On-call and operations model
Week 1-2: Core CS Fundamentals
- Day 1-3: Data structures review + coding
- Day 4-7: Algorithms + leetcode (medium problems)
- Day 8-10: System design patterns
- Day 11-14: Linux internals review
Week 3-4: Networking Deep Dive
- Review your protocol implementations
- Document architecture decisions
- Practice explaining complex concepts simply
- Prepare diagrams for your work
- Code protocol snippets from memory
Week 5: Mock Interviews
- Technical: Code on whiteboard/screen
- System design: Full session
- Behavioral: STAR method responses
Week 6: Final Polish
- Review weak areas
- Practice common questions
- Prepare your questions for interviewer
- Rest and confidence building
- TCP/IP Illustrated (Stevens) - Reference
- Computer Networks (Tanenbaum) - Concepts
- UNIX Network Programming (Stevens) - Sockets
- Linux Kernel Networking (Rami Rosen) - Implementation
- Designing Data-Intensive Applications - System design
- System Design Interview (Alex Xu) - Design patterns
- LeetCode (focus on graphs, trees, heaps)
- HackerRank network programming problems
- System design questions from Pramp/Interviewing.io
- RFC documents for protocols you implemented
- Cisco/Juniper design guides
- IETF working group documents
- Network engineering blogs
-
Be ready to whiteboard: Practice drawing network diagrams, data structures, and architectures
-
Explain your thinking: Talk through your approach, don't just code silently
-
Ask clarifying questions: Show you understand requirements before solving
-
Discuss trade-offs: Nothing is perfect; show you understand pros and cons
-
Own your experience: You have 19 years - be confident but humble
-
Prepare code samples: Have 2-3 code snippets from your work ready to discuss (sanitized)
-
Know your metrics: Performance numbers, scale, impact of your work
-
Stay current: Show you're not stuck in old technologies
-
Communication matters: You're a principal engineer - leadership communication is critical
-
Be yourself: Your experience is valuable - trust it!