iperf ‐ #networking - five4nets/Linux-Knowledgebase GitHub Wiki

Tutorial: Using the Linux `iperf` Command

iperf is a powerful command-line tool for measuring network performance, including bandwidth, latency, and packet loss. It operates in a client-server model, allowing you to test network throughput between two systems. This tutorial covers iperf installation, basic usage, command explanations, and practical examples.

Prerequisites

Two Linux systems (one as server, one as client).
Network connectivity between the systems.
Root or sudo privileges for installation.

Installation

Install iperf on both systems. For Debian-based distributions (e.g., Ubuntu):

sudo apt update
sudo apt install iperf

For Red Hat-based distributions (e.g., CentOS, Fedora):

sudo yum install iperf

For iperf3 (a newer version):

sudo apt install iperf3  # Debian-based
sudo yum install iperf3  # Red Hat-based

Verify installation:

iperf --version
iperf3 --version

Basic Usage

iperf requires one system to act as the server and another as the client.

Starting the Server

On the server system, run:

iperf -s

For iperf3:

iperf3 -s

-s: Specifies server mode.
The server listens on the default port 5001 (iperf) or 5201 (iperf3).

Running the Client

On the client system, connect to the server (replace server_ip with the server's IP address):

iperf -c server_ip

For iperf3:

iperf3 -c server_ip

-c: Specifies client mode and the server to connect to.
This runs a 10-second test by default, measuring throughput.

Common Options

Here are key iperf/iperf3 options:

Option	Description	Example
`-p`	Specify port	`iperf -s -p 5100`
`-t`	Test duration (seconds)	`iperf -c server_ip -t 20`
`-i`	Interval for reporting (seconds)	`iperf -c server_ip -i 2`
`-u`	Use UDP instead of TCP	`iperf -c server_ip -u`
`-b`	Bandwidth limit (UDP only)	`iperf -c server_ip -u -b 10M`
`-P`	Number of parallel streams	`iperf -c server_ip -P 4`
`-f`	Format output (k, m, g for Kbps, Mbps, Gbps)	`iperf -c server_ip -f m`
`-R`	Reverse test (server sends, client receives)	`iperf3 -c server_ip -R`

Examples

Example 1: Basic TCP Test

Measure TCP bandwidth between client and server.

Server:
```
iperf -s
```
Client:
```
iperf -c 192.168.1.100 -t 15 -i 3
```
Explanation:
- Runs a 15-second test (-t 15).
- Reports every 3 seconds (-i 3).
- Output shows bandwidth (e.g., [ ID: 123] Interval: 0-15s Transfer: 1.2Gbps).

Example 2: UDP Test with Bandwidth Limit

Test UDP performance with a 5 Mbps limit.

Server:
```
iperf3 -s -p 6000
```

Client:

iperf3 -c 192.168.1.100 -p 6000 -u -b 5M -t 10

Explanation:
- Uses UDP (-u) on port 6000 (-p 6000).
- Limits bandwidth to 5 Mbps (-b 5M).
- Runs for 10 seconds.
- Output includes jitter and packet loss (e.g., Lost/Total: 0.2%).

Example 3: Parallel Streams

Test with multiple TCP streams to maximize bandwidth.

Server:
```
iperf -s
```
Client:
```
iperf -c 192.168.1.100 -P 8 -f m
```
Explanation:
- Uses 8 parallel streams (-P 8).
- Reports in Mbps (-f m).
- Useful for high-bandwidth networks.

Example 4: Bidirectional Test

Test bandwidth in both directions simultaneously (iperf3 only).

Server:
```
iperf3 -s
```
Client:
```
iperf3 -c 192.168.1.100 --bd=2
```
Explanation:
- --bd=2 runs two parallel streams
- Output shows both upload and download speeds.

Example 5: Reverse Test

Test server-to-client (iperf3 only).

Server:
```
iperf3 -s
```
Client:
```
iperf3 -c 192.168.1.100 -R
```
Explanation:
- -R: Reverses the test direction
- Useful for testing asymmetric links.

Interpreting Output

TCP: Look for Bandwidth (e.g., 1.5 Gbps) in the summary.
UDP: Check Jitter (e.g., 0.5ms) and Lost/Total for packet loss.
Parallel Streams: Sum the bandwidth of each stream to get total throughput.

Example TCP output:

[ ID: 123] Interval: 0-10s Transfer: 1125MB Bandwidth: 900Mbps

Example UDP output:

[ ID: 123] Interval: 0-10s Transfer: 50MB Bandwidth: 40Mbps Jitter: 0.3ms Lost/Total: 5/10000 (0.05%)

Troubleshooting

Connection refused: Ensure the server allows incoming traffic on the specified port (e.g., ufw allow 5201 or update iptablesiptables).
Low performance: Check network congestion, CPU usage, or try multiple streams (-P).
iperf vs. iperf3: Some options differ; use the same version on both systems for compatibility.