{
  "id": "linux-network-inspection",
  "title": "Answer Three Real Questions With Three Real Commands",
  "category": "Networking",
  "isolation_type": "shared_namespace",
  "difficulty": "Easy",
  "type": "task",
  "weight": 4,
  "description": "## Answer Three Real Questions With Three Real Commands\n\nEach networking command answers a specific question. Practice treating them that way.\n\n**Your task:**\n\n1. \"What IP address does this machine have?\" — write your `eth0` IPv4 address to `/srv/network-lab/my-ip.txt`\n2. \"What's listening on port 80?\" — confirm something is, and write `80` to `/srv/network-lab/listening-port.txt`\n3. \"What does DNS say `lab-internal.test` resolves to?\" — a hosts entry for it already exists on this machine; write the resolved IP to `/srv/network-lab/resolved-ip.txt`",
  "hints": [
    {
      "title": "Your own IP",
      "body": "`ip -4 addr show eth0` prints your interface's IPv4 address in an `inet a.b.c.d/nn` line.",
      "command": "ip -4 addr show eth0"
    },
    {
      "title": "What's listening",
      "body": "`ss -lnt` lists every TCP socket in LISTEN state and its port.",
      "command": "ss -lnt"
    },
    {
      "title": "Resolving a name",
      "body": "`getent hosts <name>` resolves a hostname using the same lookup mechanism the rest of the system uses (checks /etc/hosts, then DNS) — a reliable choice when you're not sure which one will answer.",
      "command": "getent hosts lab-internal.test"
    }
  ],
  "setup_commands": [
    { "command": "mkdir -p /srv/network-lab" },
    { "command": "grep -q lab-internal.test /etc/hosts || echo '10.99.99.42 lab-internal.test' >> /etc/hosts" }
  ],
  "validation": {
    "commands": [
      { "description": "correctly identified a real IPv4 address", "command": "cat /srv/network-lab/my-ip.txt", "expected_output": "^([0-9]{1,3}\\.){3}[0-9]{1,3}$", "match": "regex" },
      { "description": "correctly identified port 80 as listening", "command": "cat /srv/network-lab/listening-port.txt", "expected_output": "80", "match": "exact" },
      { "description": "correctly resolved lab-internal.test", "command": "cat /srv/network-lab/resolved-ip.txt", "expected_output": "10.99.99.42", "match": "exact" }
    ]
  },
  "default_namespace": "default",
  "teardown_commands": [
    { "command": "rm -rf /srv/network-lab" }
  ]
}