Iperf 2 - Network testing tool (based from 2.0.5)
This document is not done. RJM 8/24/2021
Man page: https:://iperf2.sourceforge.io/iperf-manpage.html
Iperf 2, this program, is different from the iperf 3 found at https://github.com/esnet/iperf
Each can be used to
measure network performance, however, iperf 2 and iperf 3 DO NOT interoperate.
They are completely different implementations with different strengths, capabilities and
different options. Iperf 2 took its code base from the original iperf code (that stalled at 2.0.5.)
Iperf 3 is a rewrite from scratch.
Both Iperf 2 (now at 2.1.4) and iperf 3 are both under active development (as of mid-2021)
Iperf 2 vs 3 table: https://iperf2.sourceforge.io/IperfCompare.html
See the end of the file for license conditions
Iperf 2.1.4 has many user visible changes since 2.0.13 and even more since 2.0.5 The below describes many of these user visible changes with a focus on 2.1.4 compared to 2.0.13
Iperf 2 new metrics
NetPwr
Network power: The network power (NetPwr) metric originates from Kleinrock and Jaffe circa 1980.
It is a measure of a desirable property divided by an undesirable property.
It is defined as throughput/delay. For TCP transmits, the delay is the sampled RTT times.
For TCP receives, the delay is the write to read latency. For UDP the delay is the
packet end/end latency.
Note, one must use -i interval with TCP to get this as that's what sets the RTT sampling rate.
The metric is scaled to assist with human readability.
InP
The InP metric is derived from Little's Law or Little's Lamma. LL in queuing theory is a
theorem that determines the average number of items (L) in a stationary queuing system
based on the average waiting time (W) of an item within a system and the average number
of items arriving at the system per unit of time (lambda). Mathematically,
it's L = lambda * W. As used here, the units are bytes. The arrival rate is
taken from the writes.
Iperf 2 Enhanced Reports
Much of the new outputs require -e for --enhanced-reports. This is supported on both the client and server
Client side (TCP)
Write: the number of socket write calls
Err: the number of write syscalls that returned with a non fatal error
Rtry: The sampled TCP retry value
RTT: the sampled TCP round trip time
CWND: the sampled TCP congestion window
NetPwr: the computed network power (using RTT)
Server side (TCP)
Burst Latency: The avg/min/max/stdev message latencies
cnt: the number of bursts or write messages
size: the average burst or write size
inP: the computed bytes in flight per Little's law
NetPwr: the computed network power (using burst arrival rates)
Reads: histogram of read sizes
Client side (UDP)
Write: the number of socket write calls
Err: the number of write syscalls that returned with a non fatal error
PPS: The sampled packets per second (computed as a derivative)
Server side (UDP)
Write: the number of socket write calls
Err: the number of write syscalls that returned with a non fatal error
PPS: The sampled packets per second (computed as a derivative)
-
configure '--enable-fast-sampling'
This configuration causes the iperf binary to support units of microseconds. It casues iperf to use four units of precision in it's timing interval output, i.e. 1e-4, as one example
iperf -c 192.168.1.64 -n 4 -C ------------------------------------------------------------ Client connecting to 192.168.1.64, TCP port 5001 TCP window size: 85.0 KByte (default) ------------------------------------------------------------ [ 1] local 192.168.1.133 port 56568 connected with 192.168.1.64 port 5001 [ ID] Interval Transfer Bandwidth [ 1] 0.0000-0.0172 sec 4.00 Bytes 1.86 Kbits/sec
-
'--trip-times' on the client
This option indicates to iperf a few things. First, that the user has syncrhonized the clients' and servers' clocks. A good way to do this is using Precision Time Protocol and a GPS atomic clock as a reference. This knowledge allows iperf to use many time stamps to be sender based, i.e. taken from the sender's write timestamp (which is carried in the payloads.)
The connect message on both the server and the client will indicate that '--trip-times' has been enabled.
Both UDP an TCP support '--trip-times'
iperf -c 192.168.1.64 --trip-times ------------------------------------------------------------ Client connecting to 192.168.1.64, TCP port 5001 TCP window size: 85.0 KByte (default) ------------------------------------------------------------ [ 1] local 192.168.1.133 port 56580 connected with 192.168.1.64 port 5001 (trip-times) iperf -s ------------------------------------------------------------ Server listening on TCP port 5001 TCP window size: 128 KByte (default) ------------------------------------------------------------ [ 1] local 192.168.1.64%enp2s0 port 5001 connected with 192.168.1.133 port 56580 (MSS=1448) (trip-times) (sock=4) (peer 2.1.4) on 2021-08-22 11:12:08 (PDT)
This file is part of iperf 2.
Iperf 2 is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.
Iperf 2 is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with iperf 2. If not, see https://www.gnu.org/licenses/.