Essential Options

| Option | Long Form | Description | Example | |--------|-----------|-------------|---------| | -s | --server | Run in server mode | iperf3 -s | | -c | --client | Run in client mode | iperf3 -c 192.168.1.100 | | -p | --port | Server port number | iperf3 -s -p 5202 | | -t | --time | Test duration in seconds | iperf3 -c server -t 30 | | -i | --interval | Reporting interval | iperf3 -c server -i 2 | | -P | --parallel | Number of parallel streams | iperf3 -c server -P 4 | | -u | --udp | Use UDP protocol | iperf3 -c server -u | | -b | --bandwidth | Target bandwidth | iperf3 -c server -u -b 100M | | -R | --reverse | Reverse test direction | iperf3 -c server -R | | -w | --window | TCP window size | iperf3 -c server -w 64K | | -M | --set-mss | TCP MSS size | iperf3 -c server -M 1460 |

Advanced Options

| Option | Long Form | Description | Example | |--------|-----------|-------------|---------| | -J | --json | Output in JSON format | iperf3 -c server -J | | -O | --omit | Omit initial seconds | iperf3 -c server -O 5 | | -T | --title | Test title prefix | iperf3 -c server -T "LAN Test" | | -C | --congestion | TCP congestion control | iperf3 -c server -C cubic | | -Z | --zerocopy | Use zero-copy method | iperf3 -c server -Z | | -A | --affinity | CPU affinity | iperf3 -c server -A 2 | | -B | --bind | Bind to interface | iperf3 -c server -B eth1 | | -4 | --version4 | Force IPv4 | iperf3 -c server -4 | | -6 | --version6 | Force IPv6 | iperf3 -c server -6 |

Server Configuration

Basic Server Setup

`bash

Start server on default port 5201

Start server on custom port

Start server with verbose output

Start server as daemon

Server with Specific Interface

`bash

Bind server to specific IP address

Bind server to specific interface

IPv6 server

Server Configuration File

Create a systemd service for persistent iperf3 server:

`bash

Create service file

`ini [Unit] Description=iperf3 server After=network.target

[Service] Type=simple User=iperf3 ExecStart=/usr/bin/iperf3 -s -p 5201 Restart=always RestartSec=10

[Install] WantedBy=multi-user.target `

`bash

Create user for service

Enable and start service

Client Configuration

Basic Client Tests

`bash

Simple throughput test

Test for 60 seconds with 5-second intervals

Test with 4 parallel streams

Reverse test (server sends to client)

UDP Performance Testing

`bash

Basic UDP test with 100 Mbps target

UDP test with custom packet size

UDP test measuring jitter

Bidirectional Testing

`bash

Simultaneous bidirectional test

Sequential bidirectional test

Testing Scenarios

Scenario 1: LAN Performance Testing

Objective: Test maximum throughput between two systems on the same network segment.

Server Setup: `bash

Start server with verbose logging

Client Commands: `bash

Basic throughput test

Multi-stream test

Large window size for high-speed networks

Expected Results: - Gigabit Ethernet: ~940 Mbps - 10 Gigabit Ethernet: ~9.4 Gbps - Fast Ethernet: ~94 Mbps

Scenario 2: WAN Performance Testing

Objective: Measure performance across wide area networks with higher latency.

Server Setup: `bash

Server with extended timeout

Client Commands: `bash

Long duration test with larger window

Test with congestion control optimization

Multiple parallel streams for WAN

Scenario 3: Wireless Network Testing

Objective: Evaluate wireless network performance and identify interference.

Client Commands: `bash

Basic wireless test

UDP test to measure packet loss

Bidirectional test for wireless

Scenario 4: Network Troubleshooting

Objective: Diagnose network issues and bottlenecks.

Diagnostic Commands: `bash

Test with small packets

Test with jumbo frames

CPU affinity testing

Advanced Features

JSON Output and Parsing

`bash

Generate JSON output

Parse JSON with jq

Extract specific metrics

Custom Congestion Control

`bash

List available congestion control algorithms

Test with different algorithms

Performance Comparison Table

| Algorithm | Throughput (Mbps) | Retransmissions | RTT (ms) | |-----------|-------------------|-----------------|----------| | CUBIC | 945 | 12 | 1.2 | | BBR | 952 | 8 | 1.1 | | RENO | 923 | 18 | 1.3 |

Zero-Copy and CPU Optimization

`bash

Enable zero-copy for reduced CPU usage

Set CPU affinity

Combine optimizations

Performance Optimization

TCP Window Scaling

The TCP window size significantly impacts performance, especially on high-bandwidth, high-latency networks.

Bandwidth-Delay Product Calculation: ` Optimal Window Size = Bandwidth × Round Trip Time `

Examples: `bash

For 1 Gbps link with 10ms RTT

Window Size = 1,000,000,000 bps × 0.01s = 10,000,000 bits = 1.25 MB

For 100 Mbps link with 50ms RTT

Window Size = 100,000,000 bps × 0.05s = 5,000,000 bits = 625 KB

System Tuning for High Performance

Network Buffer Tuning: `bash

Increase network buffer sizes

Apply changes

CPU and Interrupt Optimization: `bash

Check interrupt distribution

Set network interface interrupt affinity

Use specific CPU cores for iperf3

Performance Comparison Matrix

| Configuration | Single Stream | 4 Streams | 8 Streams | CPU Usage | |---------------|---------------|-----------|-----------|-----------| | Default | 940 Mbps | 940 Mbps | 940 Mbps | 15% | | Large Window | 945 Mbps | 950 Mbps | 952 Mbps | 18% | | Zero-Copy | 948 Mbps | 955 Mbps | 958 Mbps | 12% | | CPU Affinity | 950 Mbps | 960 Mbps | 965 Mbps | 14% | | Combined | 955 Mbps | 970 Mbps | 975 Mbps | 10% |

Troubleshooting

Common Issues and Solutions

Issue 1: Connection Refused `bash

Check if server is running

Check firewall rules

Solution: Start server and open firewall

Issue 2: Poor Performance `bash

Check network interface statistics

Check for errors

Monitor CPU usage during test

Issue 3: UDP Packet Loss `bash

Check receive buffer size

Increase buffer size

Debug Mode and Verbose Output

`bash

Enable debug mode

Server with detailed logging

Client with enhanced output

Network Path Analysis

`bash

Trace route to destination

Check MTU path discovery

Test with different MSS values

Real-World Examples

Example 1: Data Center Network Validation

Scenario: Validating 10 Gigabit Ethernet links between servers in a data center.

Server Configuration: `bash

Start multiple servers for parallel testing

Client Test Script: `bash #!/bin/bash SERVER="10.0.1.100" DURATION=60 RESULTS_DIR="/tmp/network_tests"

mkdir -p $RESULTS_DIR

echo "Starting network performance validation..."

Test 1: Single stream maximum throughput

Test 2: Multiple parallel streams

Test 3: Bidirectional test

Test 4: UDP performance

Parse results

Example 2: Internet Service Provider Testing

Scenario: Testing customer internet connection speeds and quality.

Automated Testing Script: `bash #!/bin/bash

ISP Speed Test Script

ISP_SERVER="speedtest.isp.com" TEST_DURATION=30 REPORT_FILE="/tmp/isp_speed_test_$(date +%Y%m%d_%H%M%S).txt"

echo "ISP Speed Test Report - $(date)" > $REPORT_FILE echo "=================================" >> $REPORT_FILE

Download speed test

Upload speed test

Latency and packet loss test

echo "Test completed. Report saved to $REPORT_FILE" `

Example 3: Wireless Network Optimization

Scenario: Optimizing wireless network performance in an office environment.

Site Survey Script: `bash #!/bin/bash

Wireless Performance Survey

ACCESS_POINT="192.168.1.1" SURVEY_POINTS=("Conference Room" "Office Area" "Kitchen" "Reception") RESULTS_DIR="/tmp/wireless_survey"

mkdir -p $RESULTS_DIR

for location in "${SURVEY_POINTS[@]}"; do echo "Testing location: $location" echo "Please move to $location and press Enter..." read # Record signal strength SIGNAL=$(iwconfig wlan0 | grep "Signal level" | awk '{print $4}' | cut -d'=' -f2) # Test throughput THROUGHPUT_RESULT=$(iperf3 -c $ACCESS_POINT -t 30 -J) THROUGHPUT=$(echo $THROUGHPUT_RESULT | jq -r '.end.sum_received.bits_per_second') # Test UDP performance UDP_RESULT=$(iperf3 -c $ACCESS_POINT -u -b 100M -t 10 -J) PACKET_LOSS=$(echo $UDP_RESULT | jq -r '.end.sum.lost_percent') # Save results cat << EOF > "$RESULTS_DIR/${location// /_}.txt" Location: $location Signal Strength: $SIGNAL dBm Throughput: $(echo "scale=2; $THROUGHPUT/1000000" | bc) Mbps Packet Loss: $PACKET_LOSS% Test Time: $(date) EOF echo "Results for $location saved." done

Generate summary report

Example 4: Network Monitoring and Alerting

Continuous Monitoring Script: `bash #!/bin/bash

Network Performance Monitor

MONITOR_SERVER="monitor.company.com" THRESHOLD_MBPS=800 CHECK_INTERVAL=300 # 5 minutes LOG_FILE="/var/log/network_monitor.log" ALERT_EMAIL="admin@company.com"

log_message() { echo "$(date '+%Y-%m-%d %H:%M:%S') - $1" | tee -a $LOG_FILE }

send_alert() { local message="$1" echo "$message" | mail -s "Network Performance Alert" $ALERT_EMAIL log_message "ALERT: $message" }

while true; do log_message "Starting network performance check" # Perform speed test RESULT=$(iperf3 -c $MONITOR_SERVER -t 10 -J 2>/dev/null) if [ $? -eq 0 ]; then SPEED_BPS=$(echo $RESULT | jq -r '.end.sum_received.bits_per_second') SPEED_MBPS=$(echo "scale=2; $SPEED_BPS/1000000" | bc) log_message "Current speed: $SPEED_MBPS Mbps" # Check if speed is below threshold if (( $(echo "$SPEED_MBPS < $THRESHOLD_MBPS" | bc -l) )); then send_alert "Network speed below threshold: $SPEED_MBPS Mbps (threshold: $THRESHOLD_MBPS Mbps)" fi # Check for retransmissions RETRANSMITS=$(echo $RESULT | jq -r '.end.sum_sent.retransmits') if [ "$RETRANSMITS" -gt 100 ]; then send_alert "High retransmission count detected: $RETRANSMITS" fi else send_alert "Network performance test failed - server unreachable" fi sleep $CHECK_INTERVAL done `

This comprehensive guide covers all aspects of using iperf3 for network performance testing, from basic installation to advanced optimization techniques and real-world implementation scenarios. The tool provides invaluable insights into network behavior and helps identify bottlenecks, optimize configurations, and validate network infrastructure performance.