How Do I Benchmark and Troubleshoot Network Adapter Performance Using iPerf?

Problem Summary

Network adapter performance issues or unexpected speed throttling are commonly caused by local network bottlenecks, driver configurations, VPN services, or Wi-Fi priority settings rather than adapter hardware defects. Establishing a direct point-to-point connection and running an iPerf benchmark isolates network bottlenecks and confirms whether the adapter is achieving its rated throughput.

Isolating the Issue

We recommend starting by isolating the issue to the lowest OSI layer and working up. The Open Systems Interconnection (OSI) model is a framework for understanding network communications and is divided into seven layers:

1. Physical - This is the physical adapters, wires between two points. It can be thought of as each discrete component for example a USB to Ethernet adapter, or Ethernet cable.
2. Data Link Layer - This layer handles the direct communications between devices, using the hardware MAC Address. Communications at this layer are blocked by a router. (MAC address) hardware: Ethernet switch
3. Network Layer - This layer includes the IP address and allows for transmitting data between routed networks. (IPv4, IPv6) hardware: Router.
4. Transport Layer - This layer handles the end-to-end message delivery, and optionally error recovery and flow control, and operates in software. (TCP, UDP). For our purposes this as high as Plugable products really interact, the three next layers are independent of our products.
5. Session Layer - Opens, manages, and closes sessions between applications.
6. Presentation Layer - This includes SSL/TLS encryption, data formats like JPEG or PNG
7. Application Layer - This is the interaction layer for most users and applications, including web pages: HTML, JavaScript etc content.

Physical

When you receive no network connection at all, try a different Ethernet cable, Ethernet switch port, or bypass any devices and connections between the computer's network port and the Ethernet switch. Intermediary devices and connections (like keystone wall sockets, IP telephony systems, etc) can cause reduced network reliability. Check for the Ethernet port Link and Activity LEDs on both the computer's Ethernet adapter, and the switch port.

Data Link and Network

For simplicity these can be combined for testing, check to see if the system is receiving an IP address with terminal commands like ipconfig /all in Windows, or ip -a -br -4 in Linux. We can also check for local network connectivity by "pinging" a local resource like the router ping 192.168.1.1 where "192.168.1.1" is the IP address of the router - this will depend on your specific network configuration.

For performance related issues testing the local network, that is devices connected by one or more Ethernet switches, or even directly connected Ethernet port to Ethernet port is the first step in narrowing down an internet slowdown, to determine if the issue is between the computer and router, or between the router and internet service provider.

Local network performance testing can take a couple of forms, the most common is a utility like iPerf3 that is specifically designed for testing or benchmark a network connection. iPerf3 is designed specifically for Linux and Unix-like operating systems, it has been ported by 3rd parties to both Windows and macOS but has some limitations.

iPerf 3 Basic Benchmark

Testing with iPerf3 requires two computers - a server and a client. Generally we recommend a Linux system for the server, this will be more stable and provide more testing options, however a Windows or macOS server may also be used for basic testing. The client computer can also be Linux, Windows, or macOS, again with some limitations for non-Linux clients that shouldn't impact this this testing.

Installing iPerf3

For Linux install iPerf3 from your package manager: for Fedora (Redhat based distributions): sudo dnf -y install iperf3, or for Ubuntu (Debian based): sudo apt update && sudo apt install iperf3.

For Windows iPerf3 has been maintained by a 3rd party on GitHub and can be downloaded by selecting the Releases on the right column.

For macOS the easiest installation is through homebrew: brew install iperf3.

Configure the Server

Connect the computer to the network - or directly to the client computer - direct connections are not covered here but you can look up how to manually set IP addresses on both computers. Then look up the IP address assigned to the server open a terminal and run the following command

• Windows: ipconfig /all
• Linux: ip -br -4 addr
• Mac: You will need to look up the IP address through the macOS Apple Menu > System Settings > Network settings menu

The server simply needs to run iPerf3 with the -s argument. Open a terminal and navigate to the iPerf3 executable (Windows - for Linux and macOS after installation iPerf3 will be in the PATH), and run the program

• Windows: iperf3.exe -s
• Linux/mac: iperf3 -s

Running a test

The most basic tests iPerf3 offers are 10-second upload or download tests, however there are many configuration options available to us. Open a terminal and navigate to the iPerf3 executable (Windows - for Linux and macOS after installation iPerf3 will be in the PATH), and run the program:

• Windows: iperf3.exe -c Server_IP
• Linux/mac: iperf3 -c Server_IP

This will start an upload test to the server and print the result after each second, and a summary result to the terminal.

We can similarly start a download test by adding the -R reverse direction flag with the following:

• Windows: iperf3.exe -c Server_IP -R
• Linux/mac: iperf3 -c Server_IP -R

Here is the example output of a download test from a local server at 192.168.1.250.

Connecting to host 192.168.1.250, port 5201
Reverse mode, remote host 192.168.1.250 is sending
[  5] local 192.168.1.90 port 39982 connected to 192.168.1.250 port 5201
[ ID] Interval           Transfer     Bitrate
[  5]   0.00-1.00   sec   112 MBytes   935 Mbits/sec                  
[  5]   1.00-2.00   sec   112 MBytes   936 Mbits/sec                  
[  5]   2.00-3.00   sec   112 MBytes   937 Mbits/sec                  
[  5]   3.00-4.00   sec   112 MBytes   936 Mbits/sec                  
[  5]   4.00-5.00   sec   112 MBytes   936 Mbits/sec                  
[  5]   5.00-6.00   sec   112 MBytes   936 Mbits/sec                  
[  5]   6.00-7.00   sec   112 MBytes   937 Mbits/sec                  
[  5]   7.00-8.00   sec   112 MBytes   936 Mbits/sec                  
[  5]   8.00-9.00   sec   112 MBytes   936 Mbits/sec                  
[  5]   9.00-10.00  sec   112 MBytes   936 Mbits/sec                  
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.04  sec  1.09 GBytes   935 Mbits/sec    0             sender
[  5]   0.00-10.00  sec  1.09 GBytes   936 Mbits/sec                  receiver

iperf Done.

Each line shows the amount of data and average speed within a 1-second interval, this is great for catching intermittent issues, brief or transient slowdowns etc.

The summary (below the dashed lines) shows the Bitrate at 935 or 936 Mbits/second - measured by the client and serve respectively, with zero Retr (Re-transmits) from the client. This is pretty typical for a gigabit Ethernet connection (1000Mbps) through a home network (in this case two Ethernet switches).

Longer tests can be run by specifying the number of seconds: -t SECONDS where SECONDS is the time in seconds, for example 600 for 10 minutes. Additional settings and options can be found in the iPerf3 documentation and manual.

What does iPerf3 tell us?

iPerf3 tests the network bandwidth between two computers, by default this uses TCP (up to OSI Layer 4), for a local network segment. If the network performance between the client and server meets the expected bandwidth then performance issues are most likely outside of this scope. Internet speed testing can test the performance from the local network to the internet resource, however internet speeds will generally be less stable than local network speeds, many ISPs (Internet Service Providers) use shared bandwidth for multiple customers which can create slow times of day (for example when people start getting home from school/work), and may have asynchronous upload and download speeds. When comparing internet speed test results we recommend keeping your internet service expectations in mind.

For internet speed tests there are many options from different providers, these generally all operate through the web browser, introducing potential slowdowns from browser extensions and configuration, VPN (Virtual Private Network) connections and more. Here are some of the more common internet-based speed tests we see.

• Netflix Fast.com
• Ookla Speedtest
• OpenSpeedTest - free and open source
• Google Fiber Speed Test

If benchmark speeds remain significantly lower than expected or the test fails to run, verify that both host computers support the targeted Ethernet link rates, test with a Cat 6a or better Ethernet cable, and temporarily disable security software that may filter local network traffic. If performance issues continue, contact Plugable support at support@plugable.com with your product model, host system specifications, and iPerf test results or PlugDebug diagnostic logs.

Applicable To

• Plugable products with Ethernet ports, or Plugable Ethernet adapters
• Systems running Windows, macOS, or Linux

If you have any questions please feel free to contact us at support@plugable.com and we'll be happy to help!

The Windows Firewall may block some networking features when the local network is not set to Private.  This article will describe the process for setting the local network, either wired Ethernet or Wi-Fi to be a Private network.

Windows 11

1 - Connect the computer to the network, either wired or wireless

2 - Open the Windows Settings: right-click on the Start Menu and select Settings from the pop-up menu

3 - On the left column select Network & internet

For Wired Networks

4 - Select the Ethernet option

5 - The connected network should be expanded, if not click on Network Connected to expand the section

6 - Select the Network profile type either Public network or Private network to suite your needs

For Wi-Fi Networks

4 - Select the Wi-Fi option

5 - Select your Wi-Fi network name properties

6 - Select the Network profile type either Public network or Private network to suite your needs

Windows 10

1 - Connect the computer to the network, either wired or wireless

2 - Open the Windows Settings - right-click on the Start Menu and select Settings from the pop-up menu

3 - Select Network & Internet fro the bottom section

4 - Select the Ethernet option from the left pane

5 - Select the Connected network from the right pane

6 - Select the Network profile type either Public network or Private network to suite your needs

Windows PowerShell

If the option does not show up in the Windows Settings GUI, for example if the network is not connected to the internet, or if you prefer to use the terminal.

1 - Open a new terminal: Right-click on the Start Menu and select Terminal 

2 - Run the following command to list the available networks

Get-NetConnectionProfile

PS C:\Users\plugable> Get-NetConnectionProfile
Name                     : Network
InterfaceAlias           : Ethernet Instance 0
InterfaceIndex           : 7
NetworkCategory          : Private
DomainAuthenticationKind : None
IPv4Connectivity         : Internet
IPv6Connectivity         : NoTraffic

3 - Run the following command to set the network to Private

Set-NetConnectionProfile -Name Network -NetworkCategory Private

Where Network is the network name from step #2 and Private can be either Public or Private

If you have any questions please feel free to contact us at support@plugable.com and we'll be happy to help!

If you're looking to upgrade your wired or wireless network speed and internet connection with a Plugable USB network adapter, you’ll want to make sure you pick the right one for your setup. The three key factors to consider are:

1. The type of network you are connecting to: Wired or Wireless (Wi-Fi)
2. The type of USB port on your computer (USB-A, USB-C, or Thunderbolt)
3. The Ethernet speed you need (Gigabit, 2.5 Gigabit, 5Gbps, or Wi-Fi)

This guide will help you quickly determine which Plugable adapter best fits your needs.

Step 1: Identify Your USB Port Type

Different Plugable adapters are designed for different USB connections. Here's how to find out what type of USB port your computer has:

• USB-A Port (Rectangular Shape) – Found on most older and some newer PCs and laptops. If your device has standard USB ports, you'll want an adapter with a USB-A connector.
• USB-C Port (Small, Oval Shape) – Found on modern laptops, tablets, and some desktops. If your computer has a USB-C or Thunderbolt 3/4 port, a USB-C adapter is a better choice.
• Thunderbolt 3 or 4 – Thunderbolt ports support USB-C accessories, so any Plugable USB-C Ethernet adapter will work.

💡 Not sure which ports your computer has? Check the manufacturer's website or look for an icon next to the port: a Lightning bolt indicates Thunderbolt ( or charging ) while a USB logo will indicate the USB version.

Step 2: Determine the Ethernet Speed You Need

Your network speed is influenced by both your internet plan and the devices on your network. Choose an adapter based on the speed you want to achieve:

💡 Check your router’s specifications to see if it supports higher speeds like 2.5Gbps before choosing a multi-gig adapter.

Step 3: Choose the Right Adapter for Your System

Now that you know your USB port type and Ethernet speed requirements, here’s a quick guide to help you select the right Plugable adapter. The best bet is to meet or exceed the internet service provider’s rated speed, or for local file transfers the speed of the other systems on the network. For example, say your ISP provides a 2Gbps internet connection, then a 2.5Gbps or 5Gbps Ethernet adapter will be a good fit, while a 1Gbps adapter will still enable internet connectivity, the maximum data rate would be limited to 50% that of the rated internet speed.

For USB-A Computers

✅ Need basic 100Mbps Ethernet? → Choose the USB2-E100
✅ Need Gigabit speeds? → Choose the USB3-E1000
✅ Need Wireless Connectivity → Choose the USB-WIFINT

For USB-C or Thunderbolt 3/4 Computers

✅ Need Gigabit speeds? → Choose the USBC-E1000
✅ Need 2.5Gbps speeds? → Choose the USBC-E2500
✅ Need 5Gbps speeds? → Choose the USBC-E5000

Frequently Asked Questions (FAQs)

Q: Can I use a USB 3.0 Ethernet adapter in a USB 2.0 port?

A: Yes, but it will be limited to USB 2.0 speeds, which may affect performance.

Q: Will these adapters work with macOS, Windows, and Linux?

A: For the most part yes, except for our USB-WIFINT relies on proprietary drivers and is not recommended for macOS, Linux, or ChromeOS systems

Q: Does a faster Ethernet adapter make my internet speed faster?

A: Only if your internet service provider (ISP) plan supports higher speeds. A 2.5Gbps adapter won’t improve speeds on a 1Gbps internet connection.

Q: Can I use a USB-C adapter with a USB-A computer using an adapter?

A: It depends. Some USB-C to USB-A adapters may work, but some are limited to USB 2.0 data rates and can affect the network performance. When possible we recommend using a native USB-A Ethernet adapter for most reliable performance.

Conclusion

Picking the right Plugable USB to Ethernet adapter comes down to knowing your USB port type and the speed you need. Whether you’re looking for a basic 100Mbps connection or blazing-fast 5Gbps speeds, Plugable has an adapter to keep you connected.

Still have questions? Reach out to Plugable’s support team via email at support@plugable.com for help choosing the best adapter for your setup!