Introduction
A slow network can significantly impact productivity and cause frustration. However, troubleshooting network issues doesn’t have to be difficult. By methodically checking common causes, I can efficiently resolve most network slowdowns. In this guide, I will walk through the step-by-step process I use to troubleshoot slow network performance.
Check Network Equipment
The first place I start is examining the physical network equipment. This includes:
Routers and Switches
- I check the status lights on routers and switches. Blinking lights or lights other than solid green often indicate an issue.
- Rebooting the routers and switches can clear temporary glitches.
- Checking the equipment logs may reveal clues like high utilization, errors, or firmware issues.
- Upgrading router and switch firmware can improve performance and fix bugs.
Cabling
- Inspecting cabling for damage or loose connections is critical.
- Testing cables with a cable tester finds faults like breaks or crimps.
- Replacing bad Ethernet cables solves many mysterious network problems.
Power Supply
- Network equipment requires steady, clean power to operate properly.
- I check that power supplies are fault-free and plugged into dedicated circuits.
- Using UPS battery backups for network hardware prevents power-related issues.
Verify Network Configuration
Improperly configured network settings frequently cause performance problems. I go through these checks:
IP Addressing
- Conflicting IP addresses on the network can severely impact connectivity and speed.
- I check devices for correct unique IP addresses in the proper subnet.
VLANs
- Incorrect VLAN configurations can prevent access to network resources.
- I verify VLAN port assignments match the device network location.
QoS Settings
- If certain traffic is prioritized incorrectly, it can choke bandwidth for other applications.
- I review QoS settings to ensure mission-critical traffic gets top priority.
Firmware and Drivers
- I check that network device firmware and drivers are up-to-date to fix bugs.
- Newer drivers and firmware also optimize performance as network standards evolve.
Check for Bottlenecks
Identifying congestion points helps locate network slowdowns. I use network monitoring tools and these techniques:
Traffic Monitoring
- At choke points, I capture traffic to see volume and identify top talkers.
- This shows if a small number of systems are consuming all bandwidth.
Link Utilization
- I check utilization at junctions like core switches and router interfaces.
- Consistent high utilization indicates oversaturated links that need upgrading.
Error Monitoring
- High error rates cause TCP retransmissions and slowdowns as packets are resent.
- Monitoring helps identify bad hardware or cabling causing excessive errors.
Test With Iperf
Iperf is an invaluable network testing tool every technician should master. It generates traffic and measures maximum bandwidth between points.
Server and Client
- I run Iperf server on one end, and client on the other to test link speed.
- This shows achievable throughput between two systems as a benchmark.
Multiple Streams
- Testing concurrently with multiple Iperf streams simulates real-world loads.
- It reveals if network capacity is constrained for multiple simultaneous connections.
Different Protocols
- I test with both TCP and UDP protocols to uncover issues specific to each.
- TCP limitations often indicate latencies or loss from routing and switching.
Check for Non-Network Issues
Sometimes the network is not the root cause of slowness. I check for problems on the computers and servers themselves:
CPU Bottlenecks
- High CPU utilization can prevent systems from processing network traffic at full speed.
- I look for processes hogging CPU cycles and unresponsive applications.
Disk Bottlenecks
- Slow disk I/O bogs down the entire computer, including network processes.
- I check for disk errors and monitor disk queue lengths.
Memory Pressure
- Insufficient memory prevents optimal network stack operation.
- I verify systems meet minimum RAM requirements and not swapping.
Driver Issues
- Buggy network drivers ruin network performance.
- I update drivers and check logs for driver errors and faults.
Contact ISP
For slow internet speeds, the problem may be outside the local network. I work with the ISP to diagnose issues:
Speed Tests
- Run speed tests at modem to verify getting provisioned bandwidth from ISP.
- Compare speed tests from local network to isolate internal vs external issues.
Circuit Errors
- Check circuits for high error rates which impede performance.
- ISP can test from their end and fix physical line problems.
Traffic Shaping
- ISP may be throttling or prioritizing certain types of traffic during congestion.
- Check with ISP if speed issues are consistent and correlated with peak hours.
Conclusion
Troubleshooting network performance is a systematic process. By following these steps, I can methodically isolate the root causes of network slowness and restore optimal speeds. Proper monitoring and diagnostics tools along with knowledge of key network components provides the means to efficiently resolve most common network issues.
