pfSense is a powerful firewall and router, but without monitoring, issues can be missed.
In this tutorial, you will learn how to monitor pfSense with PRTG Network Monitor using a basic setup.
This guide is ideal for system administrators and network engineers managing firewalls.
We will configure essential sensors to monitor firewall status, CPU usage, and network traffic.
PRTG provides real-time visibility and alerts for pfSense performance and availability.
With proper monitoring, you can quickly detect failures and prevent network downtime.
This setup works for home labs, SMB networks, and production environments.
This video is part of the PRTG Network Monitoring Tutorial Series.

Step 1: Enable SNMP on pfSense

Community string: This is the same as the SNMP password; PRTG must enter it exactly as is.

Example: prtg_snmp_2025

Bind Interface: Do not select WAN (do not make it public on the internet, it’s dangerous)

Step 2: Open the firewall for SNMP

Go to Firewall → Rules → LAN

Add rule:

• Action: Pass

• Protocol: UDP

• Source: PRTG IP

• Destination: This Firewall

• Port: 161 (SNMP)

Step 3: Add Device

IP: Enter pfSense IP

Step 4: Configure SNMP Credentials

Go to Device → Settings

SNMP Credentials

• SNMP Version: v2c

• Community String: prtg_snmp_2025

• Port: 161

Step 5: Add important sensors for pfSense

#1. Ping Sensor
• Add Sensor → Ping
• Check if pfSense is alive/dead

#2. SNMP System Uptime
• Add Sensor → SNMP System Uptime

• Determine if the firewall reboots or freezes

#3. CPU pfSense

• Add Sensor → SNMP CPU Load

Very important to detect pfSense overload

#4. Monitor Interface (WAN/LAN)
• Add Sensor → SNMP Traffic
• Select interface:
o WAN
o LAN
o OPT (if any)
View bandwidth, detect network congestion

WAN Traffic
• Monitor bandwidth
• Network congestion warning
• Beautiful, easy-to-understand graph
Errors / Discards help detect:
• Cable errors
• NIC errors
• Switch port errors
Ignore all disconnected states (default)  Avoid red warnings due to dormant/unused interfaces
Show in and out traffic as positive and negative area graph  Easiest graph to view for firewalls

Alert Threshold – WAN
Channel Type Upper / Lower Value Meaning
Traffic Total Upper Warning Upper 80 Traffic WAN > 80 Mb/s → Warning
Traffic Total Upper Error Upper 90 Traffic WAN > 90 Mb/s → Error
Errors In Upper Warning Upper 1 1 error → Warning
Errors In Upper Error Upper 10 10 errors → Error
Errors Out Upper Warning Upper 1 1 error → Warning
Errors Out Upper Error Upper 10 10 errors → Error
Discards In Upper Warning Upper 1 Packet dropped → Warning
Discards In Upper Error Upper 10 Packets dropped many times → Error
Discards Out Upper Warning Upper 1 Packet dropped → Warning
Discards Out Upper Error Upper 10 Packets dropped many times → Error
Tip: WAN traffic depends on your home bandwidth. For example, 100 Mb/s, use % → 80 Mb/s ~ 80% → correct.

Tip: WAN traffic depends on your home bandwidth. For example, 100 Mb/s, use % → 80 Mb/s ~ 80% → correct.

Alert Threshold – OpenVPN (ovpns1)
Channel Type Upper / Lower Value Meaning
Traffic Total Upper Warning Upper 10 Traffic > 10 Mb/s → Warning (depending on baseline)
Traffic Total Upper Error Upper 20 Traffic > 20 Mb/s → Error
Errors In Upper Warning Upper 1 Packet error → Warning
Errors In Upper Error Upper 5 Packet error → Error
Errors Out Upper Warning Upper 1 Packet errors → Warning
Errors Out Upper Error Upper 5 Error packet → Error
Discards In Upper Warning Upper 1 Packet abandoned → Warning
Discards In Upper Error Upper 5 Packet dropped → Error
Discards Out Upper Warning Upper 1 Packet abandoned → Warning
Discards Out Upper Error Upper 5 Packet dropped → Error
VPN traffic is usually small, so the threshold is lower than WAN, and so are errors/discards Low → Set low to catch anomalies.

#5. Disk usage pfSense
• Monitor hard drive (especially if there is a lot of logging)
• Sensor: SNMP Custom
• Channel Name: Disk Usage
• OID: 1.3.6.1.4.1.2021.9.1.9.1
• Value Type: Absolute (integer)
• Unit: %
Alert:

• Upper Warning: 80

• Upper Error: 90

#6. Monitor State Table
Add sensor: SNMP Custom Advanced
Current states
1.3.6.1.4.1.12325.1.200.1.1.1.0

Enable Limits

Upper Warning: > 70% Max
Upper Error: > 85% Max