# Testing your VPS network speed (speedtest CLI, test files, iperf3)
Source: https://vpsdime.com/knowledgebase/troubleshooting/testing-network-speed
Last reviewed: 2026-07-02
Summary: How to measure your VPS's real throughput, Ookla's Speedtest CLI on the server, our Looking Glass test files (100MB/1GB/10GB per location), and iperf3 between machines you control, plus how to interpret single-stream vs multi-stream results and distance effects before concluding "the port is slow".

## What this is

How to measure your VPS's actual **throughput**, and how to read the numbers before concluding something is slow. (If your problem is lag, jitter, or packet loss rather than transfer speed, that's the [network problems guide](https://vpsdime.com/knowledgebase/troubleshooting/network-problems), the two pair well.)

## What to expect before you test

- Your VPS sits on a fast **10 Gbps uplink**, but a speed test never measures "the port" in isolation, it measures the whole path to whatever server you test against, and the slowest link on that path wins.
- **A single TCP connection slows down with distance.** That's TCP physics (latency limits how fast one stream can ramp), so one stream to a nearby server can pull gigabits while one stream across the Atlantic pulls far less, on a perfectly healthy connection. **Multiple parallel streams** show the real capacity.
- **Testing from home measures your home line.** If your home plan is 100 Mbit, every download from your VPS tops out there, that's not the VPS.

## Method 1: Speedtest CLI on the VPS

Ookla's official CLI is the quickest meaningful test. Install it on the VPS (their [install instructions](https://www.speedtest.net/apps/cli) cover every distro), then:

```
speedtest
```

It picks a nearby server and reports down/up/latency. Two tips: test against a **nearby** server first (that's the fair test of the VPS's connection), and if you want a specific target, list servers with `speedtest -L` and pick one with `-s ID`. Skip the older community `speedtest-cli` Python script, it underreports at high speeds.

## Method 2: our Looking Glass test files

The [Looking Glass](https://vpsdime.com/looking-glass) publishes **100MB, 1GB, and 10GB test files for each of our locations** (for example `https://lg.dallas.vpsdime.com/1GB.test`, pick your location on the page).

- **From your home browser:** downloading one tests the path **from our network to you**, this is the number to check before ordering, or when "downloads from my VPS are slow at home".
- **From a VPS:** `wget -O /dev/null https://lg.dallas.vpsdime.com/1GB.test` tests between our locations or from another provider's box.

One caution: **test downloads count against your VPS's monthly [traffic allowance](https://vpsdime.com/knowledgebase/acceptable-use/bandwidth-overage)** like any other transfer, prefer the 1GB file for routine checks and save the 10GB one for when you need it.

## Method 3: iperf3 between machines you control

For measuring one specific path properly (VPS to VPS, VPS to office), iperf3 is the gold standard, run both ends yourself:

```
iperf3 -s                          # on the receiving machine
iperf3 -c OTHER.HOST -P 4          # from the sending machine, 4 parallel streams
iperf3 -c OTHER.HOST -P 4 -R       # same, reversed direction
```

`-P 4` (or 8) shows path capacity rather than single-stream TCP behavior, and `-R` matters because [the two directions can differ](https://vpsdime.com/knowledgebase/troubleshooting/network-problems). Open TCP port 5201 in your own firewall on the server side for the test, and close it after.

## Reading the results

- **One stream slow, parallel streams fast:** normal TCP-over-distance behavior, not a fault. Judge capacity by the parallel number.
- **Slow to one destination, fast to others:** a path/peering issue toward that destination, run [mtr both ways](https://vpsdime.com/knowledgebase/troubleshooting/network-problems) and send us the traces.
- **Slow everywhere, tested from home:** test from the VPS itself (Method 1); if the VPS tests fine, the bottleneck is your local line.
- **Genuinely slow from the VPS to nearby servers too:** now it's worth a [ticket](https://vpsdime.com/open-ticket/), include the speedtest/iperf3 outputs, which server you tested against, when, and an mtr.

## Related questions

- "How do I run a speed test on my VPS?"
- "Why is a single download from my VPS slow?"
- "Do you have test files I can download?"
- "How do I test bandwidth between two servers with iperf3?"
- "Does speed testing use up my traffic allowance?"