How to Test Connection Speed Between Two Machines
I want to access my cloud computes/volumes merge my networks together
How to quickly test network speed can be a valuable skill. In this blog post, we’ll walk through a simple way to test the network speed between two Linux servers using the netcat (GNU version), commonly referred to as nc. This lightweight utility is often used for networking tasks such as port scanning, data transfers, and service testing, but it can also be used for measuring throughput between systems.
tl;dr
Do this:
- On ‘downloading’ server run
nc -l -p 12345 > /dev/null - On ‘uploading’ server run
dd if=/dev/zero bs=1M count=1000 | nc <server_B_IP> 12345
That’s it. You’ll probably get something like 1048576000 bytes (1.0 GB) copied, 5.24369 s, 200 MB/s printed on the ‘uploading’ server. If you don’t, read on.
Prerequisites
- Two Debian-based Linux servers (referred to here as Server A and Server B)
- Route between the two servers
- Netcat (GNU version) installed on both servers
Step-by-Step Process
1. Install Netcat (if not already installed)
First, ensure that Netcat is installed on both servers. Most Linux distributions include it by default, but if not, you can install it using the package manager for your specific distribution.
For Debian/Ubuntu-based systems:
sudo apt update
sudo apt install netcat
2. Start Netcat in Listening Mode on Server B
On Server B (the receiving server), we need to start Netcat in “listening mode” on a specific port. You can choose any unused port—here, we’ll use port 12345 for illustration.
Run the following command on Server B:
nc -l -p 12345 > /dev/null
Explanation
-l: This tells Netcat to listen for incoming connections.-p 12345: Specifies port 12345.> /dev/null: Discards the received data. We are not interested in the actual data transfer but in testing the speed, so we send the data to/dev/null.
3. Send Data from Server A
On Server A (the sending server), we can now send data to Server B. To measure throughput, we will use the dd command to generate data and pipe it to Netcat, which will send the data to Server B.
Run the following command on Server A:
dd if=/dev/zero bs=1M count=1000 | nc <server_B_IP> 12345
Explanation
dd if=/dev/zero: This generates a stream of null bytes from/dev/zero.bs=1M: This sets the block size to 1 megabyte.count=1000: This specifies the number of blocks to send. Here, we’re sending 1000 MB (1 GB) of data.| nc <server_B_IP> 12345: This pipes the data to Netcat, which sends it to the IP address of Server B on port 12345.
4. Measure Transfer Speed
As the data is transferred from Server A to Server B, the dd command will output statistics, including the total time taken and the speed at which the data was transmitted.
You will see an output similar to this on Server A:
1000+0 records in
1000+0 records out
1048576000 bytes (1.0 GB) copied, 5.24369 s, 200 MB/s
In this example, the network speed between the two servers is approximately 200 MB/s.
Interpreting Results
The output from the dd command will provide a good indication of the network speed between Server A and Server B. However, keep in mind that factors such as disk I/O performance, CPU load, and network congestion can also affect the speed measurements. For more accurate results, consider running the test multiple times and averaging the results.
Additional Considerations
- Routing: Ensure the route between machines is as expected.
- Firewall Rules: Ensure that the port you’re using (e.g., 12345) is open on both servers. If necessary, modify the firewall rules to allow traffic through this port.
- Bandwidth: The measured throughput is the raw data transfer speed between the two servers. Depending on the link and conditions, real-world application performance may vary.
- Compression: If you’re sending compressible data over the network, the transfer rate might be higher than expected due to compression during transmission. Confirm with data generated from
/dev/random.
Conclusion
Testing network speed between two Linux servers using Netcat is a quick and easy process. While tools like iperf and nload are commonly used for similar tests, Netcat provides a lightweight, no-frills alternative that works just as well in many cases. By combining it with the dd command, you can generate traffic and measure the speed between servers, helping you diagnose network bottlenecks or performance issues in your infrastructure.
Feel free to experiment with different data sizes and block sizes to get a more comprehensive view of your network performance!