ARPScanner: A Beginner’s Guide to Network Discovery

How to Use ARPScanner for Rapid LAN InventoryARPScanner is a lightweight, efficient tool designed to quickly discover devices on a local area network (LAN) using ARP (Address Resolution Protocol) requests. For network administrators, security professionals, and IT technicians who need a fast snapshot of active hosts, ARPScanner provides low-noise, accurate discovery that works where higher-level protocols may be blocked or unreliable. This guide walks through installing ARPScanner, planning your scan, running scans safely and effectively, interpreting results, automating inventory tasks, and troubleshooting common issues.

Why use ARP-based scanning?

Fast and low-overhead: ARP is a link-layer protocol; ARP requests travel only on the local broadcast domain, making scans fast and contained.
Effective in restricted environments: Many devices respond to ARP even if firewalls or host-based filters block higher-layer probes (ICMP, TCP).
Accurate MAC address collection: ARP returns MAC addresses directly, essential for vendor identification and asset tagging.
Safe for LANs: Because ARP scanning stays within the local subnet, it avoids generating traffic across routers and reduces the risk of accidental external scanning.

Installation

ARPScanner implementations vary; this guide assumes a typical Linux environment and covers two common approaches: a standalone ARPScanner utility and using arp-scan (a widely available CLI tool).

Install arp-scan (Debian/Ubuntu)

sudo apt update sudo apt install arp-scan

Install arp-scan (CentOS/RHEL)

sudo yum install epel-release sudo yum install arp-scan

macOS (Homebrew)

brew install arp-scan

If you have a custom ARPScanner binary, place it in /usr/local/bin and ensure it is executable:

sudo cp arp-scanner /usr/local/bin/arp-scanner sudo chmod +x /usr/local/bin/arp-scanner

Permissions and safety

ARP scanning typically requires raw socket access or packet injection privileges; run with root or via sudo.
Notify your network team before running broad scans—ARP traffic is benign but can trigger monitoring alerts.
Limit scans to authorized networks. ARPScanner should only be used on networks you own or administratively control.

Basic usage

Using arp-scan is straightforward. The simplest command scans your current local subnet:

sudo arp-scan --localnet

To scan a specific subnet:

sudo arp-scan 192.168.1.0/24

Common useful flags:

–interface=eth0 (choose a specific NIC)
–ignoredups (suppress duplicate MACs)
–retry=NUM (number of retries for unanswered hosts)
–timeout=TIME (per-host timeout)

Example scanning a VLAN interface:

sudo arp-scan --interface=eth0.100 10.10.100.0/24

Interpreting results

Typical arp-scan output includes the IP address, MAC address, and vendor name (from the MAC OUI). Example output line:

192.168.1.23  00:1A:2B:3C:4D:5E  Cisco Systems, Inc

Key points:

MAC vendor names help identify device types (e.g., Cisco, Apple).
Duplicate MACs may indicate virtual machines, virtualization NAT, or MAC spoofing.
Unrecognized OUIs appear as the vendor field being blank or listed as “(unknown)”.

Advanced techniques

Whitelisting and blacklisting subnets

Create a list of subnets to include or exclude during routine inventories to focus scans and reduce noise.

Rate-limiting and timing

If the network is sensitive, slow the scan:

sudo arp-scan --localnet --retry=2 --timeout=200

Combined approaches

Combine ARP scanning with other tools for richer inventories:

Map ARPScanner results to an IPAM or CMDB.
Use Nmap for targeted deeper probes only on hosts discovered by ARPScanner.
Query vendor APIs based on MAC OUIs for device models.

Automating and integrating results

Export arp-scan output to CSV, then import into spreadsheets or asset databases. Example:
```
sudo arp-scan 192.168.1.0/24 | awk '{print $1","$2","$3}' > lan_inventory.csv 
```

Schedule regular scans with cron; rotate logs and maintain a history to detect changes. Cron example (daily at 02:00):

0 2 * * * root /usr/bin/arp-scan --localnet | /usr/bin/awk '{print $1","$2","$3}' >> /var/log/lan_inventory/arp-$(date +%F).csv

Alerting: compare current scan to baseline and trigger alerts on new/removed MACs.

Use cases

Initial network discovery during onboarding or site surveys.
Rapid detection of rogue devices and unauthorized endpoints.
Asset reconciliation: matching MACs to owned equipment lists.
Troubleshooting connectivity in isolated broadcast domains.

Limitations

Local-only: ARP scanning cannot reach hosts beyond routers.
False negatives: Devices with static ARP entries or power-savings may not respond.
MAC spoofing: MAC addresses can be forged, so combine ARP data with other telemetry for high-confidence identification.

Troubleshooting

No results: ensure correct interface and that you’re on the target subnet. Use ifconfig/ip addr to verify.
Sparse results: check switch port security, client firewalls, or VLAN misconfigurations.
Vendor names missing: update OUI database (arp-scan typically ships with an OUI file you can refresh).

Update arp-scan’s OUI database:

sudo update-oui # or replace /usr/share/arp-scan/oui.txt with a current list

Example workflow: Rapid inventory for a 100-host office

Connect a laptop to the office network and confirm interface (eth0).

Run initial scan:


sudo arp-scan --interface=eth0 192.168.50.0/24 > initial_scan.txt

Parse results into CSV and import into asset tracker.

Run selective nmap on interesting hosts:


nmap -sV -p22,80,443 -iL hosts_to_probe.txt

Schedule nightly ARP scan and diff against baseline to detect changes.

Conclusion

ARPScanner (or arp-scan) is an ideal first-line tool for quick, low-impact LAN inventory. It provides reliable MAC-level device discovery, is fast to run, and integrates easily into automated workflows. Paired with additional tools and a disciplined process, ARP-based scanning can dramatically shorten the time needed for accurate network inventories and ongoing asset monitoring.