Network & Operating Systems

This section explains the networking and OS fundamentals that backend engineers use in real incidents.

Learning Goals

After finishing this section, you should be able to:

• Explain packet flow from application code down to network hardware.
• Debug common production failures: timeout, reset, DNS failure, MTU issues.
• Interpret key tools: ss, tcpdump, traceroute, dig, strace.
• Choose practical optimizations for latency and throughput.

TCP/IP Five-Layer Model

Three-Way Handshake (Quick View)

Reading Path

1. Start from Physical Layer to understand latency and regional topology.
2. Move to Data Link and Network Layer for ARP, MTU, routing, NAT.
3. Deep dive into Transport Layer for TCP performance and reliability.
4. Finish with Application Layer and protocol-level troubleshooting.

Core Chapters

• Physical Layer
• Data Link Layer
• Network Layer
• Transport Layer
• Application Layer
• Troubleshooting Overview

Focused Topics

• DNS Resolution
• TLS Handshake
• Linux Performance Tuning
• Container Networking
• Network Performance Optimization
• Network Security Basics
• System Calls for Debugging

Quick Toolbelt

# Connectivity and path
ping -c 4 8.8.8.8
traceroute example.com

# DNS
DIG +short example.com

# TCP sockets
ss -tulpen

# Packet capture
tcpdump -i any port 443 -nn

Practice Advice

• Reproduce issues with a minimal command first.
• Confirm whether the failure is DNS, TCP, TLS, or app logic.
• Capture evidence before changing configuration.