Network Scanner

Scan networks to discover devices, gather MAC addresses, vendors, and hostnames. Includes safety checks to prevent accidental scanning of public networks.

Discover and identify devices on local or remote networks using nmap. Gathers IP addresses, hostnames (via reverse DNS), MAC addresses, and vendor identification.

Safety First: Includes built-in protection against accidentally scanning public IP ranges or networks without proper private routing — preventing abuse reports from hosting providers.

Requirements

• nmap - Network scanning (apt install nmap or brew install nmap)
• dig - DNS lookups (usually pre-installed)
• sudo access recommended for MAC address discovery

Quick Start

# Auto-detect and scan current network
python3 scripts/scan.py

# Scan a specific CIDR
python3 scripts/scan.py 192.168.1.0/24

# Scan with custom DNS server for reverse lookups
python3 scripts/scan.py 192.168.1.0/24 --dns 192.168.1.1

# Output as JSON
python3 scripts/scan.py --json

Configuration

Configure named networks in ~/.config/network-scanner/networks.json:

{
  "networks": {
    "home": {
      "cidr": "192.168.1.0/24",
      "dns": "192.168.1.1",
      "description": "Home Network"
    },
    "office": {
      "cidr": "10.0.0.0/24",
      "dns": "10.0.0.1",
      "description": "Office Network"
    }
  },
  "blocklist": [
    {
      "cidr": "10.99.0.0/24",
      "reason": "No private route from this host"
    }
  ]
}

Then scan by name:

python3 scripts/scan.py home
python3 scripts/scan.py office --json

Safety Features

The scanner includes multiple safety checks to prevent accidental abuse:

1. Blocklist — Networks in the blocklist config array are always blocked
2. Public IP check — Scanning public (non-RFC1918) IP ranges is blocked
3. Route verification — For ad-hoc CIDRs, verifies the route uses private gateways

Trusted networks (configured in networks.json) skip route verification since you've explicitly approved them.

# Blocked - public IP range
$ python3 scripts/scan.py 8.8.8.0/24
❌ BLOCKED: Target 8.8.8.0/24 is a PUBLIC IP range

# Blocked - in blocklist  
$ python3 scripts/scan.py 10.99.0.0/24
❌ BLOCKED: 10.99.0.0/24 is blocklisted

# Allowed - configured trusted network
$ python3 scripts/scan.py home
✓ Scanning 192.168.1.0/24...

Commands

# Create example config
python3 scripts/scan.py --init-config

# List configured networks
python3 scripts/scan.py --list

# Scan without sudo (may miss MAC addresses)
python3 scripts/scan.py home --no-sudo

Output Formats

Markdown (default):

### Home Network
*Last scan: 2026-01-28 00:10*

| IP | Name | MAC | Vendor |
|----|------|-----|--------|
| 192.168.1.1 | router.local | AA:BB:CC:DD:EE:FF | Ubiquiti |
| 192.168.1.100 | nas.local | 11:22:33:44:55:66 | Synology |

*2 devices found*

JSON (--json):

{
  "network": "Home Network",
  "cidr": "192.168.1.0/24",
  "devices": [
    {
      "ip": "192.168.1.1",
      "hostname": "router.local",
      "mac": "AA:BB:CC:DD:EE:FF",
      "vendor": "Ubiquiti"
    }
  ],
  "scanned_at": "2026-01-28T00:10:00",
  "device_count": 2
}

Use Cases

• Device inventory: Keep track of all devices on your network
• Security audits: Identify unknown devices
• Documentation: Generate network maps for documentation
• Automation: Integrate with home automation to detect device presence

Tips

• Use sudo for accurate MAC address detection (nmap needs privileges for ARP)
• Configure your local DNS server for better hostname resolution
• Add configured networks to skip route verification on every scan
• Add networks you can't reach privately to the blocklist to prevent accidents
• Extend MAC_VENDORS in the script for better device identification