Network Bandwidth Testing with Iperf3

Introduction

This document provides instructions for performing network bandwidth tests using iperf3 on FreeBSD or Linux systems with 1Gbps interfaces. iperf3 is a powerful tool for measuring network performance, including TCP and UDP throughput.

Prerequisites

• iperf3 installed on both the client and server machines.
• Access to a command-line interface on both machines.
• Basic understanding of network concepts (TCP/UDP, bandwidth).

TCP Bandwidth Test

TCP is a connection-oriented protocol that provides reliable, ordered delivery of data. This test measures the maximum TCP throughput between two hosts.

On the server machine, start iperf3 in server mode:

# iperf3 -s

On the client machine, connect to the server and run the test.

# iperf3 -c <server_ip_address>

• Interval: The time range of the measurement.
• Transfer: The amount of data transferred during the interval.
• Bitrate: The data transfer rate (bandwidth) in bits per second.
• Retr: The number of TCP retransmissions.
• Cwnd: TCP congestion window size.

Interpretation:

• The Bitrate value indicates the TCP throughput. In a 1Gbps network, you should typically see values around 900+ Mbps, considering protocol overhead.
• A high retr value indicates network congestion.
• The sender and reciever lines show the results from each side of the connection.

UDP Bandwidth Test

On the server machine, start iperf3 in server mode with UDP:

# iperf3 -s -u

On the client machine, connect to the server and run the UDP test:

# iperf3 -c <servers_ip_address> -u -b 1G

• -u: Enables UDP mode.
• -b 1G: Sets the target bandwidth to 1 Gigabit per second.
• You can adjust the -b parameter to test different bandwidths.

Interpretation:

• The Bitrate value indicates the UDP throughput.
• Jitter The variation in packet arrival time. Should be low in a stable network.
• Lost/Total Datagrams The number of lost packets and the total number of packets sent. Should ideally be 0/Total. Any packet loss indicates potential issues.
• A high packet loss indicates network congestion or errors.

Bidirectional Bandwidth Tests

This test measures the bandwidth in both directions simultaneously.

On the server machine, start iperf3 in server mode:

# iperf3 -s

On the client machine, connect to the server and run the bidirectional test:

# iperf3 -s <server_ip_address> -b 1G -R

• -R : Runs the test in reverse mode, resulting in a bi-directional test.
• -b 1G: sets the bandwidth to 1G.