ネットワークインターフェースとIP

A network interface is your machine's doorway to a network — physical (Ethernet/Wi-Fi card) or virtual. Linux names them eth0, wlan0, enpXsX.

The ip a command (short for ip addr show) lists every interface and its details — your primary window into Linux network settings.

In ip a output, watch for the status flags, link/ether (your MAC), inet (IPv4), and inet6 (IPv6). We'll unpack each next.

A MAC address is the manufacturer-assigned hardware ID for your NIC — six hex pairs like 00:1A:2B:3C:4D:5E, living at Layer 2.

An IP address is a logical label for finding devices across networks. Unlike a MAC it can change per network, and it operates at Layer 3.

IPv4 is the most common form: a 32-bit number in dotted-decimal like 192.168.1.10 — four values 0–255, part network, part host.

CIDR notation adds a slash, like /24, marking how many bits name the network. A smaller number means a larger network.

The loopback interface lo uses 127.0.0.1 and always points at the local machine — perfect for testing apps without touching the physical network.

Consider the following (simplified) ip a output for an interface. Which line shows its MAC address?

Recap: interfaces are your connection points, ip a reveals their details, MAC IDs hardware (Layer 2), IP marks logical location (Layer 3), IPv4 uses CIDR, and lo is local-only.