Network Tools

Overview

Network diagnostic tools are essential for troubleshooting, monitoring, and understanding network behavior. This section covers the most commonly used command-line tools that every network engineer and developer should know.

Tool Categories

graph TD
    A[Network Tools] --> B[Packet Analysis]
    A --> C[Connectivity Testing]
    A --> D[Connection Inspection]
    A --> E[HTTP/Transfer]
    B --> F[Wireshark]
    B --> G[tcpdump]
    C --> H[ping]
    C --> I[traceroute]
    D --> J[netstat]
    D --> K[ss]
    E --> L[curl]
    E --> M[wget]

Quick Reference

Tool	Purpose	Layer	Common Use
ping	Test connectivity	L3 (ICMP)	“Is the host reachable?”
traceroute	Path discovery	L3	“What’s the route to the host?”
netstat	Connection inspection	L4	“What connections are open?”
tcpdump	Packet capture (CLI)	L2-L7	“What packets are flowing?”
Wireshark	Packet analysis (GUI)	L2-L7	“Deep packet inspection”
curl	HTTP client	L7	“Test HTTP endpoints”

When to Use What

flowchart TD
    A[Network Problem] --> B{Can you reach the host?}
    B -->|No| C[ping / traceroute]
    B -->|Yes| D{Is the service running?}
    D -->|No| E[netstat / ss]
    D -->|Yes| F{Is the data correct?}
    F -->|No| G[Wireshark / tcpdump]
    F -->|Yes| H{HTTP-specific issue?}
    H -->|Yes| I[curl -v]
    H -->|No| J[OSI layer analysis]

Interview Questions

Q: You can’t connect to a server. What tools would you use and in what order? A: 1) ping — Is the host reachable? 2) traceroute — Where does the path break? 3) telnet <host> <port> — Is the port open? 4) curl -v — Is the service responding correctly? 5) tcpdump — What packets are being sent/received?
Q: What’s the difference between tcpdump and Wireshark? A: tcpdump is a CLI packet capture tool — lightweight, scriptable, runs on servers. Wireshark is a GUI packet analyzer — powerful visualization, protocol dissection, filtering. Use tcpdump on remote servers, Wireshark for deep analysis.
Q: How do you check if a port is open? A: telnet host port, nc -zv host port, nmap -p port host, or ss -tlnp (on the server). For external checks, use curl host:port or online port scanners.

Summary

Mastering network tools is essential for troubleshooting. Start with ping/traceroute for connectivity, netstat/ss for connections, tcpdump/Wireshark for packet analysis, and curl for HTTP debugging.

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