MikroTik High CPU Usage – Troubleshooting Guide

Introduction

High CPU usage on MikroTik routers is a common issue that can lead to slow internet speeds, packet loss, VPN disconnections, and unstable network performance. Even powerful routers can suffer from high CPU load if certain features are misconfigured or traffic patterns change.

This article explains the most common reasons for high CPU usage on MikroTik RouterOS and provides a clear troubleshooting process to identify and fix the problem.

Problem Description

The MikroTik router shows consistently high CPU usage, sometimes reaching 80–100%. Network performance degrades, latency increases, and services such as VPNs, queues, or routing protocols may become unstable.

High CPU usage can be constant or occur only during peak traffic hours.

Common Symptoms

• CPU usage remains above normal levels
• Internet speed drops significantly
• High latency or packet loss
• VPN connections disconnect or slow down
• Router becomes unresponsive in WinBox or WebFig

Quick Checks Before Troubleshooting

1. Check CPU usage and process list
2. Identify if the issue happens during peak traffic
3. Check RouterOS version and uptime
4. Verify recent configuration changes

These checks help determine whether the issue is configuration-related or traffic-related.

Possible Causes

FastTrack Disabled or Not Working

FastTrack significantly reduces CPU usage by bypassing certain firewall processing. If it is disabled or blocked by other rules, CPU usage increases.

Heavy Firewall or Mangle Rules

Complex firewall filter rules, mangle rules, or excessive logging can consume significant CPU resources.

Excessive Traffic or DDoS Attacks

Unexpected traffic spikes, scans, or attacks can overload the router’s CPU.

Queues and Bandwidth Management

Simple queues and queue trees, especially per-user queues, are CPU-intensive.

VPN Encryption Overload

VPN protocols such as IPsec, L2TP with IPsec, or SSTP require encryption, which can heavily load the CPU on lower-end devices.

Outdated RouterOS Version

Older RouterOS versions may contain performance issues or bugs affecting CPU usage.

Step-by-Step Solution

Step 1: Identify CPU-Heavy Processes

Check which process is consuming CPU.

Also review:

This shows which features are using the most CPU.

Step 2: Enable or Fix FastTrack

Ensure FastTrack is enabled and not blocked by other firewall rules.

FastTrack should be placed near the top of firewall rules.

Step 3: Review Firewall and Mangle Rules

• Disable unnecessary rules
• Reduce logging
• Avoid overly complex mangle rules

Test CPU usage after temporarily disabling rules to isolate the issue.

Step 4: Check Queues Configuration

• Reduce the number of simple queues
• Avoid per-connection queues if possible
• Consider upgrading hardware for heavy queue usage

Queues can quickly overload small routers.

Step 5: Review VPN Usage

If VPN traffic is heavy:

• Reduce encryption where possible
• Limit number of VPN users
• Consider using WireGuard for better performance

Encryption is CPU-intensive on MikroTik devices.

Step 6: Check Traffic Patterns

Use built-in tools to identify traffic spikes.

Look for:

• Abnormally high traffic
• Repeated connections from unknown sources

Step 7: Update RouterOS

Ensure RouterOS is updated to a stable version.

Updates often improve performance and stability.

Verification and Testing

After applying fixes:

• CPU usage should stabilize
• Network latency should decrease
• Router responsiveness should improve
• VPN and routing stability should return

Monitor CPU usage during peak hours for accurate results.

Best Practices

• Always use FastTrack when possible
• Keep firewall rules clean and minimal
• Monitor CPU usage regularly
• Choose hardware suitable for traffic and VPN load

Common Mistakes

• Disabling FastTrack without understanding impact
• Excessive logging on firewall rules
• Running heavy VPN encryption on low-end routers
• Ignoring CPU spikes during peak usage

Final Thoughts

High CPU usage on MikroTik routers is usually caused by configuration choices rather than hardware failure. Features like firewall rules, queues, and VPN encryption can quickly overwhelm the CPU if not planned carefully. By identifying the root cause and applying targeted fixes, you can restore stable performance and extend the life of your MikroTik device.