PRTG – P7 How to Monitor pfSense with PRTG (Basic Monitoring Setup)

pfSense is a powerful firewall and router, but without monitoring, issues can easily go unnoticed. A firewall may appear operational while CPU overload, interface congestion, or state table exhaustion silently impact your network performance.

In this tutorial, you will learn how to Monitor pfSense with PRTG Network Monitor using a structured basic monitoring setup. This guide is ideal for system administrators and network engineers managing firewall infrastructure in home labs, SMB networks, and production environments.

We will configure essential sensors to monitor firewall availability, CPU usage, WAN/LAN traffic, VPN activity, disk usage, and state table utilization. With proper alert thresholds in place, PRTG provides real-time visibility and proactive notifications.

By implementing this monitoring strategy, you can quickly detect failures, performance bottlenecks, and abnormal traffic behavior before they cause downtime.

This video is part of the PRTG Network Monitoring Tutorial Series.

🔧 Step 1: Enable SNMP on pfSense

To Monitor pfSense, SNMP must be enabled first.

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

Example:

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

Exposing SNMP on WAN is a major security risk. Always restrict it to internal interfaces only.

🔐 Step 2: Open the Firewall for SNMP

Navigate to:

Firewall → Rules → LAN

Add rule:

• Action: Pass
• Protocol: UDP
• Source: PRTG IP
• Destination: This Firewall
• Port: 161 (SNMP)

This rule allows the PRTG server to query pfSense securely over SNMP.

🖥 Step 3: Add Device in PRTG

Add a new device in PRTG.

IP: Enter pfSense IP

This registers the firewall as a monitored device.

⚙ Step 4: Configure SNMP Credentials

Go to:

Device → Settings → SNMP Credentials

Configure:

• SNMP Version: v2c
• Community String: prtg_snmp_2025
• Port: 161

The community string must match exactly what was configured in pfSense.

📊 Step 5: Add Important Sensors for pfSense

Now we configure the core monitoring components required to properly Monitor pfSense.

#1. Ping Sensor

• Add Sensor → Ping

Purpose:

• Check if pfSense is alive or dead

This is the most basic availability check.

#2. SNMP System Uptime

• Add Sensor → SNMP System Uptime

Purpose:

• Determine if the firewall reboots or freezes

Unexpected uptime resets may indicate crashes or power issues.

#3. CPU pfSense

• Add Sensor → SNMP CPU Load

Very important to detect pfSense overload.

High CPU usage may indicate heavy traffic, IDS/IPS load, VPN encryption stress, or attack attempts.

#4. Monitor Interface (WAN/LAN)

• Add Sensor → SNMP Traffic
• Select interface:
o WAN
o LAN
o OPT (if any)

Purpose:

View bandwidth and detect network congestion.

WAN Traffic Monitoring

• 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

Traffic Total
Upper Warning: 80 → Traffic WAN > 80 Mb/s → Warning
Upper Error: 90 → Traffic WAN > 90 Mb/s → Error

Errors In
Upper Warning: 1 → 1 error → Warning
Upper Error: 10 → 10 errors → Error

Errors Out
Upper Warning: 1 → 1 error → Warning
Upper Error: 10 → 10 errors → Error

Discards In
Upper Warning: 1 → Packet dropped → Warning
Upper Error: 10 → Packets dropped many times → Error

Discards Out
Upper Warning: 1 → Packet dropped → Warning
Upper Error: 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)

Traffic Total
Upper Warning: 10 → Traffic > 10 Mb/s → Warning (depending on baseline)
Upper Error: 20 → Traffic > 20 Mb/s → Error

Errors In
Upper Warning: 1 → Packet error → Warning
Upper Error: 5 → Packet error → Error

Errors Out
Upper Warning: 1 → Packet errors → Warning
Upper Error: 5 → Error packet → Error

Discards In
Upper Warning: 1 → Packet abandoned → Warning
Upper Error: 5 → Packet dropped → Error

Discards Out
Upper Warning: 1 → Packet abandoned → Warning
Upper Error: 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

Purpose:

• Monitor hard drive (especially if there is a lot of logging)

Add sensor:

• Sensor: SNMP Custom
• Channel Name: Disk Usage
• OID:

• Value Type: Absolute (integer)
• Unit: %

Alert:

• Upper Warning: 80
• Upper Error: 90

Log-heavy environments can fill storage quickly, causing system instability.

#6. Monitor State Table

Add sensor:

• SNMP Custom Advanced

Current states OID:

Enable Limits:

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

State table exhaustion can cause connection failures and dropped sessions.

🚀 Why You Must Monitor pfSense Properly

When you properly Monitor pfSense, you gain:

• Real-time firewall visibility

• Early detection of overload conditions

• WAN congestion awareness

• VPN anomaly detection

• Disk and state table protection

• Reduced downtime risk

A firewall is the core of your network. Without monitoring, failures are reactive. With PRTG, monitoring becomes proactive.

📌 Final Thoughts

You have now configured a complete basic monitoring setup to Monitor pfSense using PRTG Network Monitor.

By enabling SNMP, opening secure firewall rules, configuring credentials, and adding essential sensors such as Ping, Uptime, CPU, WAN traffic, VPN traffic, Disk Usage, and State Table monitoring, you now have full visibility into firewall health and performance.

This structured approach ensures your pfSense environment remains stable, secure, and optimized.

In the next tutorial, we will continue expanding advanced monitoring capabilities within the PRTG ecosystem.