A PRTG alternative that licenses devices, not sensors

Paessler PRTG is a capable on-premises monitor. The problem most teams hit is not the product. It is the sensor: one license unit per ping, per CPU, per disk, and — by Paessler’s own guidance — one sensor per switch port. A 48-port core switch is one device in the rack and dozens of sensors on the invoice.

ZenPlus licenses the same way the NOC thinks: one license per unique IP. Every interface, sensor, and element on that device is included. NetFlow, NCM, maps, alerting, and reports sit in the same console, on-premises.

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What a PRTG alternative has to get right

PRTG teams are not looking for “another dashboard.” They are looking for three things:

1. Cost that does not grow when you add a port. Paessler documents that a sensor is one monitored aspect of a device (CPU, disk, port traffic) and that teams typically need about 5–10 sensors per device, with one sensor per switch port.
2. On-premises data. PRTG can stay on-prem. So can ZenPlus. The replacement has to keep telemetry, credentials, and reports inside your boundary.
3. One operator path. Device health, interface utilization, flow, config backup, and alerts without a second product and a second license conversation.

ZenPlus is built for that replacement. See also the device vs sensor licensing guide. OSS peers: LibreNMS alternative, Zabbix alternative. See also the Observium alternative.

Worked example

Worked example (honest math)

Estate: 40 × 24-port access switches + 10 routers + 20 servers = 70 devices.

Using Paessler’s own rules of thumb (one sensor per switch port, plus a handful of device sensors):

If your network is 20 ICMP-only devices and almost no port-level traffic, PRTG 500 at $200/mo can be cheaper than ZenPlus Professional. The crossover is interface-dense networks, which is most campus and data-center fabrics.

• 40 switches × 24 ports = 960 port-traffic sensors
• 40 switches × 3 device sensors (ping / CPU / memory) = 120
• 10 routers × 8 = 80
• 20 servers × 6 = 120
• Total ≈ 1,280 sensors → PRTG 2500 at $742/mo = $8,904/year
• Same estate on ZenPlus Professional: 70 devices × $5 × 12 = $4,200/year
• Every switch port, NetFlow, and NCM included in that tier — no sensor-cap upgrade when you enable the 25th interface on a stack

Migration

How a PRTG migration actually runs

Zentryc does not charge a migration license. Device count on the quote is unique IPs, not ports.

1. Inventory sensors, not just devices. Export the sensor tree. Count port-traffic sensors. That number is the business case.
2. Stand up ZenPlus on a VM (Ubuntu 22.04/24.04, one-line installer). Free tier covers 10 devices forever; paid eval is 30 days full-feature.
3. Point SNMP, WMI/WinRM, and flow exporters at the appliance. Discovery and maps come up in the same console.
4. Run both for 2–4 weeks. Compare alert noise, interface coverage, and the quote: sensors vs IPs.
5. Cut over notifications (email, channels) and retire PRTG sensors in batches, starting with the densest switches.