Why does `iperf` report huge values for bandwidth?

Question

When I try to run iperf on local server it reports reasonable values

iperf -c 127.0.0.1 -p 631
------------------------------------------------------------
Client connecting to 127.0.0.1, TCP port 631
TCP window size: 2.50 MByte (default)
------------------------------------------------------------
[  3] local 127.0.0.1 port 42824 connected with 127.0.0.1 port 631
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  2.40 MBytes  2.01 Mbits/sec

But when I connect to any remote server it reports ridiculously huge values

iperf -c www.google.com -p 80
------------------------------------------------------------
Client connecting to www.google.com, TCP port 80
TCP window size: 85.0 KByte (default)
------------------------------------------------------------
[  3] local x.x.x.x port 45329 connected with 110.164.12.55 port 80
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  0.00 � ��s  14746527068517650432 Bytes/sec

Looks like an overflow of some kind! I'm using a PPP connection from a USB EVDO modem to connect to the Internet and my iperf version is iperf version 2.0.5 (08 Jul 2010) pthreads.

Why is this happening?

Answer 1

iperf requires you to have access on both ends. On one end you run iperf -s aka server mode, on the other iperf -c IP aka client which should connect to the server with address IP. You can't just point the client to random open port and expect it to work. It needs the iperf server on the other side.