基本的なネットワークコマンド

Time for the command line. You'll learn ping, ip, traceroute, and netstat — the core tools for inspecting and diagnosing connectivity.

ping is your first reachability check: it sends ICMP echo requests and times the replies, telling you if a host is up and how fast it responds.

Just type ping plus an IP or hostname. The -c flag limits how many packets you send — run this to try it.

The ip command is the modern replacement for older tools like ifconfig. It views and configures interfaces, addresses, and routes.

Run ip addr show (or ip a) to list every interface with its MAC, IPv4/IPv6 addresses, and state — your snapshot of what's connected.

The routing table tells Linux where to send traffic. Inspect it with ip route show (or ip r) to see routes and gateways.

traceroute maps the path packets take to a host, revealing each router (hop) and its timing — great for pinpointing where delays creep in.

traceroute sends packets with rising TTL values. Each hop decrements TTL; when it hits zero, that router replies and reveals itself.

netstat shows network statistics — active connections, routing tables, and interface stats. Handy for seeing which ports are open.

You're trying to quickly determine if your Linux machine has an internet connection by checking if a remote server is online and responding. Which command would you use?

Recap of your toolkit: ping checks reachability, ip shows interfaces and routes, traceroute maps the path, and netstat lists connections and ports.