Proactive Free Network Scanner

Discover every device on your network, monitor availability, and get alerted. Free to start.

What does a free network scanner find on your network?

A network scan typically returns a list: IP addresses, MAC addresses, hostnames, device types. That's useful as a starting point, but a static list goes stale the moment someone adds a device, swaps hardware, or spins up a new VM. The value of a scanner depends on how current that inventory stays, not just how complete it was on day one.

PRTG's auto-discovery handles the scan and keeps going after it. Discovered devices get sensors assigned automatically, so your inventory reflects what's actually on the network right now. Getting started costs nothing — the trial gives you full access with no credit card required, and a freeware edition is available after for smaller environments.

What Paessler PRTG discovers and monitors: Windows, Linux, and macOS systems · Routers · Switches · Firewalls · Printers · Wi-Fi access points · IoT devices · Bandwidth

Discovery protocols used: SNMP (v1/v2c/v3) · ICMP · WMI · ARP · DNS · TCP

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PRTG is compatible with all major vendors, products, and systems

Stay Informed Across Your Entire Network

Get a Full Device Inventory Without Touching Every Device Manually

Building an accurate device inventory is straightforward when discovery does the work. PRTG's auto-discovery scans any IP range or subnet you define and builds that list automatically: IP addresses, MAC addresses, hostnames, device types, all organized without manual input. Domain-joined environments can pull directly from Active Directory, supporting up to 1,000 computers, which covers most setups without needing to define ranges at all.

Scans any IP range or subnet you define
Returns IP addresses, MAC addresses, hostnames, and device types
Covers routers, switches, firewalls, Windows/Linux/macOS systems, and printers
Active Directory integration for domain-joined environments, up to 1,000 computers

From One-Time Scan to Continuous Network Monitoring

Point-in-time scanners (e.g. Nmap) give you a snapshot, PRTG gives you what comes after. Discovered devices get sensors assigned automatically, and those sensors keep polling on whatever interval you configure. When something goes down or becomes unreachable PRTG sends an alert via email, SMS, or push. Schedule auto-discovery to run periodically and your inventory stays current as the network grows, without anyone remembering to do it.

Sensors monitor device availability continuously after discovery
Scheduled auto-discovery keeps inventory current as the network changes
Alerts via email, SMS, and push when availability changes
Covers your entire local network, not just the segment the tool runs on

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Start monitoring your infrastructure in minutes. No professional services, no complex configuration, no risk.

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PRODUCT OVERVIEW

Check Open TCP Ports Across Your Network. No Command Line Needed

TCP port visibility across your routers, servers, and firewalls is useful for security checks, service validation, and troubleshooting. PRTG has two dedicated sensors for this. The Port v2 sensor monitors individual TCP ports on any device — configure it once and it keeps checking. The Port Range sensor does the same across successive port ranges. Both return open/closed status and time-to-connect, and both store results historically so you have a full record of how that port has behaved over time, not just its current state.

Individual TCP ports or full port ranges per device
Covers common services including RDP and DNS
Full history retained, not just current state
Configured and reviewed in the PRTG web interface, no CLI required

Scan Segmented Networks, Multiple Subnets, and Remote Locations

Most free network scanners only see the subnet they're installed on. VLANs, multiple office locations, segmented network zones: separate tool runs per segment, every time. That gets old quickly.

PRTG handles multi-subnet environments and distributed networks from a single configuration. Define multiple IP ranges in one discovery setup and deploy remote probes at separate network segments or physical locations — each probe scans locally and reports everything back to your central PRTG instance. One dashboard, full picture, without managing a separate tool for each segment.

Multiple subnets and IP ranges in one discovery configuration
Remote probes extend scanning to separate segments and physical locations
All results report to a single central PRTG dashboard
Supports distributed office networks, VPNs, and segmented enterprise environments

How PRTG Scans and Discovers Network Devices

PRTG doesn't rely on a single method to find what's on your network. It runs a combination of protocols simultaneously, each pulling different information depending on what a device supports and how your network is configured. Here's what happens under the hood.

ICMP (Ping)

Discovery starts with ICMP echo requests sent across your defined IP range. Any address that responds gets flagged as active. Discovery typically starts with ICMP reachability checks. Once sensors are created, PRTG continuously records response time and packet loss, helping you build a performance baseline over time.

SNMP (v1/v2c/v3)

For routers, switches, and managed hardware that supports it PRTG queries standard system OIDs and retrieves device name, description, uptime, and interface data. v2c covers most environments. If you need authentication and encryption, SNMP v3 is supported. Configuration is done on the device side; PRTG then uses the provided credentials to query the device.

ARP

PRTG can resolve IPv4 addresses to MAC addresses via ARP during discovery. (ARP is an IPv4 mechanism; IPv6 uses Neighbor Discovery.) This is how device types get identified and how PRTG decides which icon and sensor recommendations apply to each discovered device.

WMI and DNS

On Windows systems WMI pulls system-level information other protocols can't reach. DNS lookups then run against all discovered IPs to resolve hostnames. Between those two the raw address list turns into something actually readable, device names, types, and roles rather than a column of IP addresses someone has to cross-reference manually.

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PRTG vs. Running Network Scans Manually

FEATURE	Manual Scanning Manual Scanning	With PRTG With PRTG
Device discovery	Manual Scanning One-time scan, manual re-run	With PRTG Scheduled auto-discovery
Continuous monitoring	Manual Scanning X	With PRTG Sensors run on defined intervals
Alerts when a device goes down	Manual Scanning X	With PRTG Email, SMS, push
GUI (no CLI required)	Manual Scanning Partial	With PRTG Full web interface
Built-in reporting	Manual Scanning Limited / manual	With PRTG Built-in reporting features
Multi-subnet / segmented networks	Manual Scanning Manual per subnet	With PRTG Multiple IP ranges + remote probes

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”Adopting PRTG has been like going from being in the dark to being in the light. Before, we had limited visibility into what was happening in the infrastructure and in the network. Now, however, thanks to the comprehensive dashboard and real-time notifications, we receive constant updates on the status of facilities and services, and our way of working has gone from passive to proactive.”

Luca Meneghesso, Senior IT infrastructure and Security Specialist

Banca Profilo

”GESAC increasingly focuses on innovation to improve the quality of services offered and the experience of passengers handled every day by Naples Airport. Thanks to PRTG, we finally have unified, automatic, and continuous monitoring of the airport network and can guarantee quick and timely interventions.”

Domenico Ciervo, GESAC ICT Manager

Naples International Airport

”As an international company, PRTG is ideal for us. If something went down half way across the world, we wouldn’t be woken up – we can rely on PRTG to identify the problem and alert us before it occurs – enabling the right person, in the right time zone to resolve the problem. At the end of the day, if we’re to provide an internal network experience for our employees that meets expectations, we need a tool like PRTG to be successful.”

Barry Kelly, Systems Engineer

Skyscanner

Paessler PRTG Network Monitor licenses & pricing

Choose the PRTG Network Monitor subscription that's best for you.

License Name	Price	License Details	Get started	Pricing Details
PRTG 500	^$200	per month paid annually	Buy now Buy now	Enough to monitor multiple aspects of 50 devices
PRTG 1000	^$358	per month paid annually	Buy now Buy now	Enough to monitor multiple aspects of 100 devices
PRTG 2500	^$742	per month paid annually	Buy now Buy now	Enough to monitor multiple aspects of 250 devices
PRTG 5000	^$1,300	per month paid annually	Buy now Buy now	Enough to monitor multiple aspects of 500 devices
PRTG 10000	^$1,642	per month paid annually	Buy now Buy now	Enough to monitor multiple aspects of 1000 devices

Over 100,000 Customers Worldwide Love Paessler

Free Network Scanner: Frequently Asked Questions

How is PRTG different from Nmap, Advanced IP Scanner, or Fing?

Nmap, Advanced IP Scanner, and Fing are solid for a one-time scan. They tell you what's on your network right now. Once the scan finishes though you're on your own until you run the next one, nothing alerts you if something changes in between.

What PRTG adds is continuous monitoring after discovery. Sensors keep polling your devices and alert you when something goes wrong. Worth being honest about scope here: PRTG isn't Nmap in a penetration testing context and doesn't try to be. For ongoing network visibility with alerting it's a different category of tool, and the distinction is usually pretty obvious once you've needed both at the same time.

Does PRTG scan Wi-Fi networks and wireless devices?

Yes. Auto-discovery can discover devices on both wired and wireless networks as long as they are IP-reachable from the probe and the required protocols (e.g., ICMP/SNMP/WMI) are permitted. Wi-Fi access points, wireless clients, any device with an IP address gets discovered and monitored. ICMP, SNMP, ARP, DNS don't differentiate between wired and wireless connections so neither does the discovery process.

Can PRTG scan multiple subnets or VLANs?

Yes. Multiple IP ranges can be defined within a single auto-discovery configuration so PRTG isn't limited to the subnet it's installed on. For separate network segments or physical locations you deploy a remote probe, which scans its local network and reports everything back to your central PRTG instance.

One setup, whole infrastructure. Though "whole infrastructure" depends on how many probes you deploy and where.

Does PRTG detect shared folders and network shares?

Yes. The Network Share sensor monitors SMB/CIFS shares and checks accessibility, file count, and folder size. It requires the LanmanServer service running on the target machine, which is worth confirming before you deploy it at scale. Also this sensor has higher performance impact than most, so it's not something you'd want to roll out across hundreds of devices without planning for that.

How many devices can I monitor for free?

PRTG has a freeware edition with no time limit and a full-featured 30-day trial with no sensor restrictions. For the exact numbers on what's included check the current pricing page, that's where the up-to-date details live.

Does PRTG scan UDP ports?

PRTG’s built-in port-check sensors focus on TCP. For UDP-based services, PRTG typically monitors service availability at the application/protocol level (e.g., DNS), rather than performing generic raw UDP port scans.

Not natively. The Port v2 and Port Range sensors both work over TCP. There's no raw UDP port scanning

For UDP-based services PRTG can check at the application level instead. DNS resolution via the DNS sensor is a good example of that approach. But if you need raw UDP port scanning Nmap is still the right tool for that job, no point pretending otherwise.