Best Free Network Performance Test tool - Iperf

According to wikipedia Iperf "is a commonly used network testing tool that can create TCP and UDP data streams and measure the throughput of a network that is carrying them. Iperf is a modern tool for network performance measurement written in C++." So far it is best free software to test network throughput I found. 

1. Download iperf 2 from http://iperf.fr/.

2. Running on one of your remote machine from command line as iperf server (ip address 100.99.136.66).

C:\Tools>iperf -s

------------------------------------------------------------

Server listening on TCP port 5001

TCP window size: 8.00 KByte (default)

------------------------------------------------------------

[188] local 100.99.136.66 port 5001 connected with 100.94.200.14 port 48410

[ ID] Interval       Transfer     Bandwidth

[188]  0.0-10.0 sec   121 MBytes   101 Mbits/sec

3. Run iperf as client from another machine (ip address 100.94.200.14) of your network to evaluate the network throughput based on TCP connection.

C:\tools>iperf -c 100.99.136.66

------------------------------------------------------------

Client connecting to 100.99.136.66, TCP port 5001

TCP window size: 8.00 KByte (default)

------------------------------------------------------------

[1912] local 100.94.200.14 port 48410 connected with 100.99.136.66 port 5001

[ ID] Interval       Transfer     Bandwidth

[1912]  0.0-10.0 sec   121 MBytes   101 Mbits/sec

4. Send 100MBytes data for testing

iperf -c 100.99.136.66 -n 100m

5. Bi-direction test

Simultaneous bi-directional bandwidth measurement: (-d argument)

To measure the bi-directional bandwidths simultaneousely, use the -d argument. If you want to test the bandwidths sequentially, use the -r argument (see previous test).

By default (ie: without the -r or -d arguments), only the bandwidth from the client to the server is measured.

C:\tools> iperf -c 100.99.136.66  -d

------------------------------------------------------------

Server listening on TCP port 5001

TCP window size: 85.3 KByte (default)

------------------------------------------------------------

------------------------------------------------------------

Client connecting to 10.1.1.1, TCP port 5001

TCP window size: 16.0 KByte (default)

------------------------------------------------------------

[ 5] local 10.6.2.5 port 60270 connected with 10.1.1.1 port 5001

[ 4] local 10.6.2.5 port 5001 connected with 10.1.1.1 port 2643

[ 4] 0.0-10.0 sec 76.3 MBytes 63.9 Mbits/sec

[ 5] 0.0-10.1 sec 1.55 MBytes 1.29 Mbits/sec

6. Parallel TCP connections

Parallel connections can be useful if you need to saturate the bandwidth of a link.  The bandwidth of a single TCP session can be greatly affected by the size of the receive window and the latency of the link.

iperf -s -i 1 (-i 1 means update terminal every second)

iperf -c 192.168.1.1 -t 30 -P 10

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