discover-printers-arp

name	discover-printers-arp
description	Use when mDNS discovery fails or the user wants to scan all devices on the subnet.

Discover Printers via ARP

Scan the local subnet using ARP to find all active devices, then identify likely printers by MAC OUI (vendor prefix).

When to use

• Bonjour/mDNS is not available or found no results
• Printer is on the same subnet but not advertising mDNS
• Network-wide device inventory needed
• Firewall is blocking port 5353 (mDNS)

Inputs to gather

• Optional: --interface — specific network interface (e.g. eth0; auto-detected if unset)
• Optional: --vendor-filter — filter by vendor name (e.g. "HP" to show only HP devices)

Procedure

1. Auto-detect interface. If --interface not provided, derive the primary LAN interface:

   IFACE=$(ip -o -4 route show to default | awk '{print $5; exit}')
   echo "Scanning on interface: $IFACE"
   

   Stop if no default route found; ask user to specify --interface manually.

2. Check for root/sudo. Test if arp-scan is installed:

   command -v arp-scan >/dev/null || { echo "arp-scan not found. Install with: sudo apt-get install arp-scan"; exit 1; }
   

   If not installed, stop and show the apt command.

3. Prompt for sudo if needed. If not running as root, show:

   This scan requires sudo privilege to access raw network sockets.
   Running: sudo arp-scan --localnet -i <interface>
   

4. Run ARP scan. Execute:

   sudo arp-scan --localnet -i "$IFACE" 2>/dev/null
   

5. Parse output and identify printers. For each line with an IP and MAC, cross-reference the MAC OUI (first 3 octets) against a built-in vendor list:

   • 08:00:69 → Xerox
   • 08:52:BA → HP
   • 1C:23:62 → HP
   • 4C:80:93 → Brother
   • 74:6F:F7 → Epson
   • 5C:F9:38 → Canon
   • A4:B6:D3 → Kyocera
   • 00:00:48 → Ricoh
   • 00:1A:80 → Samsung
   • 00:14:85 → Lexmark
   • (and others as feasible)

6. Format as table:

   IP              MAC               Vendor      Likely Printer?
   192.168.1.50    08:52:BA:xx:xx:xx HP          Yes
   192.168.1.75    4C:80:93:xx:xx:xx Brother     Yes
   192.168.1.100   52:54:00:xx:xx:xx QEMU        No
   ...
   

7. Apply vendor filter. If --vendor-filter provided, show only matching rows.

Output / side effects

• Table of ARP results with vendor guesses to stdout.
• No local files modified.
• Read-only; no side effects.

Safety / constraints

• Requires sudo; will prompt the user.
• ARP scan is network-safe but may be flagged by intrusion detection on large networks.
• OUI matching is heuristic; vendor list is not exhaustive and may have false positives/negatives.
• Will not find devices that are offline or do not respond to ARP.