Lan Scanner

Network Scanner

Discover devices and scan ports on your local network.

Use when scanning LAN, finding devices, or checking open ports.

Requirements

• nmap installed (apt install nmap / brew install nmap)
• No API keys needed

Instructions

1. Determine target — detect local subnet:

   ip route | grep default | awk '{print $3}' | sed 's/\.[0-9]*$/.0\/24/'
   # or
   ifconfig | grep 'inet ' | grep -v '127.0.0.1'
   

2. ⚠️ Validate target — CRITICAL:

   • ✅ Only scan private IP ranges: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 127.0.0.0/8
   • ❌ REJECT public IPs unless user explicitly confirms ownership
   • Always confirm scan target with user before executing

3. Run scans (prefer non-root options):

   Scan Type	Command	Sudo?	Speed
   Host discovery	nmap -sn {subnet}	No	Fast
   Quick ports	nmap -F {target}	No	Fast
   All ports	nmap -p- {target}	No	Slow
   Service detection	nmap -sV {target}	No	Medium
   OS detection	sudo nmap -O {target}	Yes	Medium
   Vulnerability scan	nmap --script vuln {target}	No	Slow

4. Output format:

   ## 🔍 Network Scan Results
   **Subnet:** 192.168.1.0/24 | **Date:** YYYY-MM-DD HH:MM
   **Devices found:** 12
   
   | # | IP | Hostname | MAC | Open Ports | Services |
   |---|-----|----------|-----|-----------|----------|
   | 1 | 192.168.1.1 | router | AA:BB:CC:DD:EE:FF | 80, 443 | HTTP, HTTPS |
   | 2 | 192.168.1.10 | nas | ... | 22, 445, 8080 | SSH, SMB, HTTP |
   
   ### ⚠️ Security Notes
   - 192.168.1.10: SSH (22) open — ensure key-only auth
   - 192.168.1.15: Telnet (23) open — **insecure, disable if possible**
   

5. Highlight security concerns:

   • Open Telnet (23) — insecure protocol
   • Open FTP (21) — consider SFTP instead
   • Default HTTP ports with no HTTPS
   • Services on non-standard ports

Edge Cases

• nmap not installed: Suggest installation or fall back to ping sweep + nc port check.
• Permission denied: Non-root can't do SYN scans or OS detection. Note limitations.
• Firewall blocking: Some hosts won't respond to ping. Use -Pn to skip host discovery.
• Very large subnet (/16 or larger): Warn user it will take a long time. Suggest narrowing scope.
• VPN active: Scanned subnet may be the VPN network, not local LAN. Check ip route.

Security Considerations

• Only scan networks you own or have explicit permission to scan.
• Unauthorized port scanning may violate laws and terms of service.
• Don't share scan results publicly — they reveal network topology.
• Use sudo only when explicitly needed and justified.