Networking Fundamentals & Debugging

# network_info.py
import socket
import ipaddress

# ── Basic socket information ─────────────────────────────────
hostname = socket.gethostname()
local_ip = socket.gethostbyname(hostname)
print(f"Hostname:  {hostname}")
print(f"Local IP:  {local_ip}")

# ── DNS resolution ────────────────────────────────────────────
domain = "python.org"
ip = socket.gethostbyname(domain)
print(f"\n{domain} → {ip}")

# Reverse lookup
try:
    reverse = socket.gethostbyaddr(ip)
    print(f"{ip} → {reverse[0]}")
except socket.herror:
    print(f"No reverse DNS for {ip}")

# Get all IPs (IPv4 + IPv6)
results = socket.getaddrinfo(domain, 443, proto=socket.IPPROTO_TCP)
print(f"\nAll addresses for {domain}:443 (HTTPS):")
for family, _type, _proto, _canonname, sockaddr in results:
    family_name = "IPv6" if family == socket.AF_INET6 else "IPv4"
    print(f"  {family_name}: {sockaddr[0]}")

# ── IP address utilities ─────────────────────────────────────
network = ipaddress.ip_network("192.168.1.0/24", strict=False)
print(f"\nNetwork: {network}")
print(f"Hosts:   {network.num_addresses - 2} (first: {list(network.hosts())[0]})")
print(f"Is private: {network.is_private}")

# Check if IP is in network
test_ip = ipaddress.ip_address("192.168.1.100")
print(f"192.168.1.100 in {network}: {test_ip in network}")

# port_scanner.py, Educational port scanner for authorized use only
import socket
import concurrent.futures
from datetime import datetime

COMMON_PORTS = {
    21: "FTP", 22: "SSH", 23: "Telnet", 25: "SMTP",
    53: "DNS", 80: "HTTP", 110: "POP3", 143: "IMAP",
    443: "HTTPS", 3306: "MySQL", 5432: "PostgreSQL",
    6379: "Redis", 8080: "HTTP-Alt", 8443: "HTTPS-Alt",
    27017: "MongoDB",
}

def scan_port(host: str, port: int, timeout: float = 1.0) -> dict | None:
    """Return port info if open, None if closed."""
    try:
        with socket.create_connection((host, port), timeout=timeout):
            service = COMMON_PORTS.get(port, "unknown")
            return {"port": port, "service": service, "status": "OPEN"}
    except (socket.timeout, ConnectionRefusedError, OSError):
        return None

def scan_host(host: str, ports: list[int], workers: int = 50) -> list[dict]:
    """Scan a host for open ports using a thread pool."""
    open_ports = []
    with concurrent.futures.ThreadPoolExecutor(max_workers=workers) as executor:
        futures = {executor.submit(scan_port, host, p): p for p in ports}
        for future in concurrent.futures.as_completed(futures):
            result = future.result()
            if result:
                open_ports.append(result)
    return sorted(open_ports, key=lambda x: x["port"])

# ── Scan localhost only (safe for educational use) ────────────
target = "127.0.0.1"
ports_to_scan = list(COMMON_PORTS.keys())

print(f"Scanning {target}, {datetime.now().strftime('%H:%M:%S')}")
print(f"Ports: {len(ports_to_scan)}")
print("-" * 40)

results = scan_host(target, ports_to_scan)

if results:
    for r in results:
        print(f"  PORT {r['port']:5d}/tcp   OPEN   {r['service']}")
else:
    print("  No open ports found")

print(f"\nScan complete: {len(results)} open port(s) found")