IPERF - Guide - Revision history

Admin: Created page with "Category:Wiki '''''[https://it-arts.net/index.php/Category:Wiki Return to Wiki Index]''''' == Command Syntax == iperf3 [OPTIONS] Client mode: iperf3 -c Server mode: iperf3 -s == Client Options == === Server Selection === Connect to a server: iperf3 -c 192.168.1.10 Connect using a hostname: iperf3 -c iperf.example.com Specify the server port:
2026-07-03T12:18:57Z

Created page with "Category:Wiki '''''[https://it-arts.net/index.php/Category:Wiki Return to Wiki Index]''''' == Command Syntax == <nowiki> iperf3 [OPTIONS]</nowiki> Client mode: <nowiki> iperf3 -c <server></nowiki> Server mode: <nowiki> iperf3 -s</nowiki> == Client Options == === Server Selection === Connect to a server: <nowiki> iperf3 -c 192.168.1.10</nowiki> Connect using a hostname: <nowiki> iperf3 -c iperf.example.com</nowiki> Specify the server port: <nowiki..."

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== Command Syntax ==

<nowiki>
iperf3 [OPTIONS]</nowiki>

Client mode:

<nowiki>
iperf3 -c <server></nowiki>

Server mode:

<nowiki>
iperf3 -s</nowiki>

== Client Options ==

=== Server Selection ===

Connect to a server:

<nowiki>
iperf3 -c 192.168.1.10</nowiki>

Connect using a hostname:

<nowiki>
iperf3 -c iperf.example.com</nowiki>

Specify the server port:

<nowiki>
iperf3 -c 192.168.1.10 -p 5202</nowiki>

Specify the source address:

<nowiki>
iperf3 -c 192.168.1.10 -B 192.168.1.20</nowiki>

Specify the outgoing interface (Linux routing dependent):

<nowiki>
iperf3 -c 192.168.1.10 -B 10.0.0.2</nowiki>

=== Test Duration ===

Run a test for 30 seconds:

<nowiki>
iperf3 -c 192.168.1.10 -t 30</nowiki>

Run indefinitely until interrupted:

<nowiki>
iperf3 -c 192.168.1.10 -t 0</nowiki>

=== Interval Reporting ===

Display statistics every second:

<nowiki>
iperf3 -c 192.168.1.10 -i 1</nowiki>

Display statistics every 500 ms:

<nowiki>
iperf3 -c 192.168.1.10 -i 0.5</nowiki>

=== Parallel Streams ===

Launch four simultaneous TCP streams:

<nowiki>
iperf3 -c 192.168.1.10 -P 4</nowiki>

Launch sixteen TCP streams:

<nowiki>
iperf3 -c 192.168.1.10 -P 16</nowiki>

Parallel streams are commonly used to fully utilize high-bandwidth links when a single TCP flow is limited by congestion control or latency.

=== Reverse Mode ===

Request the server to transmit data back to the client:

<nowiki>
iperf3 -c 192.168.1.10 -R</nowiki>

Useful for validating asymmetric bandwidth.

=== Bidirectional Mode ===

Transmit simultaneously in both directions:

<nowiki>
iperf3 -c 192.168.1.10 --bidir</nowiki>

Useful for evaluating full-duplex links.

=== TCP Window Size ===

Specify the socket buffer size:

<nowiki>
iperf3 -c 192.168.1.10 -w 4M</nowiki>

Possible units:

* K
* M

=== Zero Copy ===

Reduce CPU utilization using sendfile():

<nowiki>
iperf3 -c 192.168.1.10 -Z</nowiki>

Useful on high-speed links.

=== Omit Initial Seconds ===

Ignore the first seconds of a test:

<nowiki>
iperf3 -c 192.168.1.10 -O 5</nowiki>

Useful for avoiding TCP slow-start measurements.

=== MSS ===

Specify the TCP Maximum Segment Size:

<nowiki>
iperf3 -c 192.168.1.10 -M 1400</nowiki>

Mostly used for troubleshooting MTU issues.

=== IPv4 and IPv6 ===

Force IPv4:

<nowiki>
iperf3 -4 -c server.example.com</nowiki>

Force IPv6:

<nowiki>
iperf3 -6 -c server.example.com</nowiki>

=== JSON Output ===

Produce JSON output:

<nowiki>
iperf3 -c 192.168.1.10 -J</nowiki>

Useful for automation and monitoring.

=== Log File ===

Store client output:

<nowiki>
iperf3 -c 192.168.1.10 --logfile iperf.log</nowiki>

== Server Options ==

Start a server:

<nowiki>
iperf3 -s</nowiki>

Specify a listening port:

<nowiki>
iperf3 -s -p 5202</nowiki>

Bind to a specific interface:

<nowiki>
iperf3 -s -B 192.168.1.10</nowiki>

Run only one test then terminate:

<nowiki>
iperf3 -s -1</nowiki>

Enable daemon mode:

<nowiki>
iperf3 -s -D</nowiki>

Create a log file:

<nowiki>
iperf3 -s --logfile /var/log/iperf3.log</nowiki>

== UDP Testing ==

=== Basic UDP Test ===

<nowiki>
iperf3 -c 192.168.1.10 -u</nowiki>

=== Specify Bandwidth ===

Transmit at 100 Mbit/s:

<nowiki>
iperf3 -c 192.168.1.10 -u -b 100M</nowiki>

Transmit at 1 Gbit/s:

<nowiki>
iperf3 -c 192.168.1.10 -u -b 1G</nowiki>

Unlimited transmission speed:

<nowiki>
iperf3 -c 192.168.1.10 -u -b 0</nowiki>

=== UDP Packet Length ===

Specify datagram size:

<nowiki>
iperf3 -c 192.168.1.10 -u -l 1400</nowiki>

=== UDP Results ===

UDP reports include:

* Throughput
* Packet loss
* Lost datagrams
* Jitter
* Out-of-order packets

== Authentication ==

Generate credentials:

<nowiki>
iperf3 --username user --rsa-private-key-path private.pem</nowiki>

Authenticate:

<nowiki>
iperf3 -c server --username user --rsa-public-key-path public.pem</nowiki>

This feature is primarily intended for controlled environments where multiple users access the same server.

== Examples ==

=== LAN Performance ===

Server:

<nowiki>
iperf3 -s</nowiki>

Client:

<nowiki>
iperf3 -c 192.168.1.10</nowiki>

=== 10 Gbit/s Validation ===

Server:

<nowiki>
iperf3 -s</nowiki>

Client:

<nowiki>
iperf3 -c 192.168.1.10 -P 8 -O 5 -t 60 -Z</nowiki>

=== VPN Performance ===

Server:

<nowiki>
iperf3 -s</nowiki>

Client:

<nowiki>
iperf3 -c 10.10.10.1 -R</nowiki>

=== Internet Connection ===

<nowiki>
iperf3 -c remote.example.com -P 4 -t 60</nowiki>

=== Wi-Fi Benchmark ===

<nowiki>
iperf3 -c 192.168.1.10 -P 4 -t 30</nowiki>

=== Continuous Monitoring ===

<nowiki>
watch -n 60 'iperf3 -c 192.168.1.10 -t 10'</nowiki>

== Performance Considerations ==

=== TCP Congestion Control ===

Linux supports multiple congestion control algorithms.

Display the current algorithm:

<nowiki>
sysctl net.ipv4.tcp_congestion_control</nowiki>

List available algorithms:

<nowiki>
sysctl net.ipv4.tcp_available_congestion_control</nowiki>

=== CPU Limitations ===

High-speed links above 10 Gbit/s may become CPU-bound.

Recommendations:

* Enable Zero Copy (-Z).
* Increase parallel streams.
* Disable CPU frequency scaling.
* Pin processes to dedicated CPU cores.
* Verify interrupt balancing.

=== MTU ===

Incorrect MTU values reduce throughput.

Validate MTU:

<nowiki>
ping -M do -s 1472 remote-host</nowiki>

=== Socket Buffers ===

Display Linux socket limits:

<nowiki>
sysctl net.core.rmem_max</nowiki>

<nowiki>
sysctl net.core.wmem_max</nowiki>

Increase if necessary.

=== NUMA ===

On NUMA systems:

* Place client and NIC on the same NUMA node.
* Pin CPU affinity.
* Reduce cross-node memory access.

== Security ==

=== Network Exposure ===

iperf3 servers accept arbitrary client connections.

Restrict access using:

* Firewall rules
* VPN tunnels
* Dedicated management VLANs
* Access control lists

=== Firewall ===

Default TCP port:

<nowiki>
5201/tcp</nowiki>

Restrict source addresses whenever possible.

=== Denial of Service ===

An unrestricted iperf3 server may generate significant traffic.

Recommendations:

* Enable the server only during testing.
* Use <nowiki>
-1</nowiki> for one-shot operation.
* Restrict client IP addresses.
* Avoid exposing iperf3 servers directly to the Internet.

=== Data Confidentiality ===

iperf3 traffic is not encrypted.

Use:

* WireGuard
* IPsec
* SSH tunnel
* TLS VPN

when testing across untrusted networks.

=== Authentication ===

If authentication is enabled:

* Protect private keys.
* Rotate credentials regularly.
* Restrict filesystem permissions.

== Troubleshooting ==

=== Connection Refused ===

Verify the server is running:

<nowiki>
ss -lnt | grep 5201</nowiki>

Verify firewall rules.

=== Connection Timed Out ===

Verify:

* Routing
* NAT
* Firewall
* ACLs
* VPN connectivity

=== Low Throughput ===

Increase parallel streams:

<nowiki>
iperf3 -c server -P 8</nowiki>

Increase test duration:

<nowiki>
iperf3 -c server -t 60</nowiki>

Ignore TCP slow-start:

<nowiki>
iperf3 -c server -O 5</nowiki>

=== High CPU Usage ===

Enable Zero Copy:

<nowiki>
iperf3 -c server -Z</nowiki>

Reduce logging.

Verify CPU frequency.

=== Poor UDP Results ===

Reduce requested bandwidth:

<nowiki>
iperf3 -c server -u -b 500M</nowiki>

Reduce packet size:

<nowiki>
iperf3 -c server -u -l 1200</nowiki>

Investigate switch buffering and packet drops.

=== Reverse Mode Works but Normal Mode Fails ===

Check:

* Asymmetric routing
* Firewall rules
* NAT configuration
* Policy-based routing

=== Packet Loss ===

Verify interface statistics:

<nowiki>
ip -s link</nowiki>

Capture traffic:

<nowiki>
tcpdump -i eth0</nowiki>

Check switch errors.

=== High Retransmissions ===

Possible causes:

* Congestion
* MTU mismatch
* Packet loss
* Duplex mismatch
* Faulty cabling

=== Unexpected Results in Virtual Machines ===

Verify:

* Virtio drivers
* Hypervisor CPU scheduling
* Host CPU saturation
* Virtual NIC offloading
* NUMA placement

== Useful Links ==

* https://software.es.net/iperf/
* https://github.com/esnet/iperf
* https://software.es.net/iperf/invoking.html
* https://software.es.net/iperf/faq.html
* https://software.es.net/iperf/dev.html
* https://github.com/esnet/iperf/tree/master/docs
* https://man7.org/linux/man-pages/man1/iperf3.1.html
* https://iperf.fr/
* https://wiki.linuxfoundation.org/networking/kernel_flow
* https://www.kernel.org/doc/html/latest/networking/index.html
* https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt
* https://www.rfc-editor.org/rfc/rfc6349
* https://www.rfc-editor.org/rfc/rfc793
* https://www.rfc-editor.org/rfc/rfc9293
* https://www.rfc-editor.org/rfc/rfc768

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