Testing your local area network (LAN) speed is a critical step in diagnosing performance issues and ensuring that your hardware and cabling are functioning as expected. Unlike testing your internet connection, which measures throughput to an external server, a LAN speed test isolates the performance of your internal network. This process verifies that data transfers between devices on the same network are occurring at the rates promised by your networking equipment, such as switches, routers, and Ethernet cables.
Why Test Your Internal LAN Speed?
Many users confuse slow network performance with a lack of internet bandwidth, leading to unnecessary upgrades to their service plan. However, the bottleneck is frequently within the local network itself. If you are transferring large files between computers, streaming 4K video from a network-attached storage (NAS) device, or using resource-heavy applications, ensuring your LAN can handle the load is essential. A proper test helps differentiate between internal network issues and external internet problems.
Preparation for Accurate Testing
To ensure your results are valid, you must control variables that can skew the data. You should temporarily disable any firewall or antivirus software, as these programs often inspect traffic and slow down the transfer rates. Furthermore, ensure that only the two devices involved in the test are active on the network. Background updates or cloud synchronization services running on idle machines can consume bandwidth and ruin the accuracy of your results.
Method 1: Using a Dedicated LAN Speed Test Tool
The most reliable method involves using a specialized application designed to measure raw throughput between two endpoints. These tools create a direct connection between two computers and transfer a large dummy file, calculating the speed based on the time taken. This method is superior to online speed tests because it eliminates the internet entirely, testing only the physical layer of your network.
Recommended Software and Procedure
We recommend using tools like iPerf3, JDSU Test-Um NTB100, or LAN Speed Test by Totusoft. Here is the general procedure to follow:
Install the speed test application on two computers that are connected via the LAN you wish to test.
Designate one computer as the "server" and the other as the "client."
Run the application in server mode on the first machine and client mode on the second.
Initiate the test from the client machine and record the throughput results displayed.
Method 2: Testing with a File Transfer Benchmark
A practical alternative for home users is to perform a real-world file transfer test. This involves copying a large file from one device to another and calculating the speed manually. While less precise than dedicated software, this method provides a clear indication of actual performance during common tasks.
How to Calculate Transfer Speed
To determine the speed, you need to know the file size and the time it takes to copy. For example, copying a 4 Gigabyte (GB) file that takes 40 seconds to transfer results in a speed of 0.1 GB per second. For reference, a theoretical Gigabit Ethernet (1000BASE-T) network should handle approximately 125 MB per seconds, meaning that 4 GB should take roughly 32 seconds to transfer without any overhead or hardware limitations.
