1.. _faq: 2 3iperf3 FAQ 4========== 5 6What is the history of iperf3, and what is the difference between iperf2 and iperf3? 7 iperf2 was orphaned in the late 2000s at version 2.0.5, despite some 8 known bugs and issues. After spending some time trying to fix 9 iperf2's problems, ESnet decided by 2010 that a new, simpler tool 10 was needed, and began development of iperf3. The goal was make the 11 tool as simple as possible, so others could contribute to the code 12 base. For this reason, it was decided to make the tool single 13 threaded, and not worry about backwards compatibility with 14 iperf2. Many of the feature requests for iperf3 came from the 15 perfSONAR project (http://www.perfsonar.net). 16 17 Then in 2014, Bob (Robert) McMahon from Broadcom restarted 18 development of iperf2 (See 19 https://sourceforge.net/projects/iperf2/). He fixed many of the 20 problems with iperf2, and added a number of new features similar to 21 iperf3. iperf2.0.8, released in 2015, made iperf2 a useful tool. iperf2's 22 current development is focused is on using UDP for latency testing, as well 23 as broad platform support. 24 25 As of this writing (2017), both iperf2 and iperf3 are being actively 26 (although independently) developed. We recommend being familiar with 27 both tools, and use whichever tool’s features best match your needs. 28 29 A feature comparison of iperf2, iperf3, and nuttcp is available at: 30 https://fasterdata.es.net/performance-testing/network-troubleshooting-tools/throughput-tool-comparision/ 31 32iperf3 parallel stream performance is much less than iperf2. Why? 33 iperf3 is single threaded, and iperf2 is multi-threaded. We 34 recommend using iperf2 for parallel streams. 35 If you want to use multiple iperf3 streams use the method described `here <https://fasterdata.es.net/performance-testing/network-troubleshooting-tools/iperf/multi-stream-iperf3/>`_. 36 37I’m trying to use iperf3 on Windows, but having trouble. What should I do? 38 iperf3 is not officially supported on Windows, but iperf2 is. We 39 recommend you use iperf2. 40 41 Some people are using Cygwin to run iperf3 in Windows, but not all 42 options will work. Some community-provided binaries of iperf3 for 43 Windows exist. 44 45How can I build a statically-linked executable of iperf3? 46 There are a number of reasons for building an iperf3 executable with 47 no dependencies on any shared libraries. Unfortunately this isn't 48 quite a straight-forward process. 49 50 The steps below have nominally been tested on CentOS 7.4, but 51 can probably be adapted for use with other Linux distributions: 52 53 #. If necessary, install the static C libraries; for CentOS this is 54 the ``glibc-static`` package. 55 56 #. If OpenSSL is installed, be sure that its static libraries are 57 also installed, from the ``openssl-static`` package. 58 59 #. Be sure that ``lksctp-*`` packages are not installed, because 60 as of this writing, there do not appear to be any static 61 libraries available for SCTP. 62 63 #. Configure iperf3 thusly: ``configure "LDFLAGS=--static" 64 --disable-shared`` These options are necessary to disable the 65 generation of shared libraries and link the executable 66 statically. 67 68 #. Compile as normal. 69 70 It appears that for FreeBSD (tested on FreeBSD 11.1-RELEASE), only 71 the last two steps are needed to produce a static executable. 72 73How can I build on a system that doesn't support profiled executables? 74 This problem has been noted by users attempting to build iperf3 for 75 Android systems. There are several workarounds. In order from least 76 effort to most effort: 77 78 #. Beginning with iperf-3.6, the ``--disable-profiling`` flag can be 79 passed to ``configure`` to disable the building of profiled 80 object files and the profiled executable. 81 82 #. At the time the linking of the iperf3 profiled executable fails, 83 the "normal" iperf3 executable is probably already created. So if 84 you are willing to accept the error exit from the make process 85 (and a little bit of wasted work on the build host), you might 86 not need to do anything. 87 88 #. After the configure step, there will be a definition in 89 ``src/Makefile`` that looks like this:: 90 91 noinst_PROGRAMS = t_timer$(EXEEXT) t_units$(EXEEXT) t_uuid$(EXEEXT) \ 92 iperf3_profile$(EXEEXT) 93 94 If you edit it to look like this, it will disable the build of the profiled iperf3:: 95 96 noinst_PROGRAMS = t_timer$(EXEEXT) t_units$(EXEEXT) t_uuid$(EXEEXT) 97 98 #. Similar to item 2 above, but more permanent...if you edit 99 ``src/Makefile.am`` and change the line reading like this:: 100 101 noinst_PROGRAMS = t_timer t_units t_uuid iperf3_profile 102 103 To look like this:: 104 105 noinst_PROGRAMS = t_timer t_units t_uuid 106 107 And then run ``./bootstrap.sh``, that will regenerate the project 108 Makefiles to make the exclusion of the profiled iperf3 executable 109 permanant (within that source tree). 110 111I'm seeing quite a bit of unexpected UDP loss. Why? 112 First, confirm you are using iperf 3.1.5 or higher. There was an 113 issue with the default UDP send size that was fixed in 114 3.1.5. Second, try adding the flag ``-w2M`` to increase the socket 115 buffer sizes. That seems to make a big difference on some hosts. 116 117iperf3 UDP does not seem to work at bandwidths less than 100Kbps. Why? 118 You'll need to reduce the default packet length to get UDP rates of less that 100Kbps. Try ``-l100``. 119 120What congestion control algorithms are supported? 121 On Linux, run this command to see the available congestion control 122 algorithms (note that some algorithms are packaged as kernel 123 modules, which must be loaded before they can be used):: 124 125 /sbin/sysctl net.ipv4.tcp_available_congestion_control 126 127 On FreeBSD, the equivalent command is:: 128 129 /sbin/sysctl net.inet.tcp.cc.available 130 131I’m using the ``--logfile`` option. How do I see file output in real time? 132 Use the ``--forceflush`` flag. 133 134I'm using the --fq-rate flag, but it does not seem to be working. Why? 135 You need to add 'net.core.default_qdisc = fq' to /etc/sysctl.conf for that option to work. 136 137I'm having trouble getting iperf3 to work on Windows, Android, etc. Where can I get help? 138 iperf3 only supports Linux, FreeBSD, and OSX. For other platforms we recommend using iperf2. 139 140I managed to get a Windows executable built, but why do I get a BSOD on Windows 7? 141 There seems to be a bug in Windows 7 where running iperf3 from a 142 network filesystem can cause a system crash (in other words Blue 143 Screen of Death, or BSOD). This is a Windows bug addressed in kb2839149: 144 145 https://support.microsoft.com/en-us/help/2839149/stop-error-0x00000027-in-the-rdbss-sys-process-in-windows-7-or-windows 146 147 A hotfix is available under kb2732673: 148 149 https://support.microsoft.com/en-us/help/2732673/-delayed-write-failed-error-message-when--pst-files-are-stored-on-a-ne 150 151Why can’t I run a UDP client with no server? 152 This is potentially dangerous, and an attacker could use this for a 153 denial of service attack. We don't want iperf3 to be an attack tool. 154 155I'm trying to use iperf3 to test a 40G/100G link...What do I need to know? 156 See the following pages on fasterdata.es.net: 157 158 - https://fasterdata.es.net/host-tuning/100g-tuning/ 159 - https://fasterdata.es.net/performance-testing/network-troubleshooting-tools/iperf/multi-stream-iperf3/ 160 161My receiver didn't get all the bytes that got sent but there was no loss. Huh? 162 iperf3 uses a control connection between the client and server to 163 manage the start and end of each test. Sometimes the commands on 164 the control connection can be received and acted upon before all of 165 the test data has been processed. Thus the test ends with data 166 still in flight. This effect can be significant for short (a few 167 seconds) tests, but is probably negligible for longer tests. 168 169A file sent using the ``-F`` option got corrupted...what happened? 170 The ``-F`` option to iperf3 is not a file transfer utility. It's a 171 way of testing the end-to-end performance of a file transfer, 172 including filesystem and disk overheads. So while the test will 173 mimic an actual file transfer, the data stored to disk may not be 174 the same as what was sent. In particular, the file size will be 175 rounded up to the next larger multiple of the transfer block size, 176 and for UDP tests, iperf's metadata (containing timestamps and 177 sequence numbers) will overwrite the start of every UDP packet 178 payload. 179 180I have a question regarding iperf3...what's the best way to get help? 181 Searching on the Internet is a good first step. 182 http://stackoverflow.com/ has a number of iperf3-related questions 183 and answers, but a simple query into your favorite search engine can 184 also yield some results. 185 186 There is a mailing list nominally used for iperf3 development, 187 iperf-dev@googlegroups.com. 188 189 We discourage the use of the iperf3 issue tracker on GitHub for 190 support questions. Actual bug reports, enhancement requests, or 191 pull requests are encouraged, however. 192 193 194