• iperf (short for “IP performance”) is a client/server throughput (bandwidth) measurement tool
• iperf uses a TCP-connection (by default) to sent traffic at maximum possible speed and measuring the capacity (troughput or bandwidth) of the connection.
  This is similar to a file-download (or upload) and calculating the bandwith by dividing the file-size by the copy duration.
• Advantages of iperf (compared to a file-copy):
  • no need to create a large file and manual copying
  • bandwidth calculation is automatic and is shown at certain intervals (configurable)
  • test upload and download sequentially or concurrently
  • test upload and download with multiple parallel channels

Example of a Windows client and a server on a 100 Mbps LAN :

Note that 94 Mbps is the maximum TCP-performance that you can expect on a 100 Mbps Ethernet connection, because you loose approximately 6% of bandwidth due to protocol and header overhead.

To put it this way: Layer-4 (TCP) bandwidth = 94% of Layer-2 (Ethernet) bandwidth

Technically:

• layer-4 (TCP) bandwidth is called “throughput”,
  that is including protocol-overhead, transmit delays and retransmissions due to packet-loss.
• layer-2 (Ethernet) bandwidth is the “line-speed” (eg. 10/100/1000Mbps)

• Save this file: iperf-1.7.0-win32.exe.bin
• Rename to .exe

Check the MD5-checksum if you want to verify the file integrity:

md5sum iperf-1.7.0-win32.exe 
624b6717901c90f3ca254f2f91ab15f3  iperf-1.7.0-win32.exe

• Wikipedia → Iperf
• original iperf page → http://dast.nlanr.net/Projects/Iperf/
• original iperf docs → http://dast.nlanr.net/Projects/Iperf/iperfdocs_1.7.0.php
• local copy of “iperf v2.0.0 User docs”
  → http://john.de-graaff.net/docs/iperf_user_docs_v2.0.0/
• local copy of iperf source code (debian-4.0)
  → http://john.de-graaff.net/docs/iperf_2.0.2.orig.tar.gz
• Linux Redhat packages → http://dag.wieers.com/packages/iperf/
• Linux Debian packages → http://packages.debian.org/etch/iperf
• graphical frontend jperf → http://code.google.com/p/xjperf/
• other informational page on iperf → http://openmaniak.com/iperf.php

Typical usage server-side:

iperf -s -w64000 -i1

Typical usage client-side:

iperf -c 12.12.1.1 -w64000 -i1 -t5 -r

Options:

-s       Server mode (listening)
-c <ip>  Client mode, connect to <ip>
-i 1     Display speed each 1 second
-m       Display MSS and MTU (when done)
-w 64k   Change TCP Windows size (helps on Windows hosts)
-t 4     Run 4 secs instead of default 10 sec
-r       do Reverse: first push Client->Server,
         then pull Client<-Server 
         (use to test symmetricy bandwidth and duplex mismatches)
-d       do Dual: push and pull at the same time 
         (test full-duplex)
-P 4     use 4 channels parallel (default 1) (note: 'P' is capital)

• iperf default TCP-port is 5001
• TCP-connection (SYN) is “client → server”
• Stream is “client → server”, so data-PUSH from client→server.
  So from client perspective this is upload bandwidth!
  (use -r to test sequentially upload and then download)
• Info on Duplex Mismatch