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1429 posts

Uber Geek
+1 received by user: 189


# 251119 9-Jun-2019 21:25
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I have been having issues with international speeds recently and at a loss as to why.


@NickMack and the team at 2Degrees have been an awesome help with this issue; sending out some test gear to assist with troubleshooting the issue.  (Thanks again guys!)


The conclusion of the testing with 2D was that my network, Internet connection and PCs were all fine, the problem was something specific to Windows.  Speeds in Linux were fine.


However, nothing I tried made any difference until I discovered this article:




As a result I discovered that iPerf3 v3.1.3 for Windows (the latest stable release) comes bundled with a version of Cygwin1.dll (2.5.1) which has a hard-coded TCP window size setting of 278,775.


This causes results to be limited to 12.6Mb/s per thread.


This is why iPerf speeds in Linux are much better that in Windows.


Updating the Cygwin dll to the latest version resolves this issue and I now get the International speeds I am expecting when testing with iPerf.


I have informed the iPerf devs of this issue.




As a side-note, speeds with and nperf to the US are still pretty much rubbish.  I'm not sure why, because they used to be fine.  At then end of the day iPerf (with updated Cygwin1.dll) is the most reliable testing method by far.

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187 posts

Master Geek
+1 received by user: 77

  # 2257076 12-Jun-2019 22:04
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You're probably better off with WSL rather than a Cygwin build.

'That VDSL Cat'
10398 posts

Uber Geek
+1 received by user: 2500


  # 2257077 12-Jun-2019 22:13
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Yup, window size being fixed will certainly do it. Moment i saw the title i was going to comment on tcp/ip tuning...






it will prove that your connection is able to consistently perform, but in your day to day you will still be expecting the applications and kernel to do it's thing.


Windows has also had a few cases of some REALLY bad drivers...




i'd blame the slow speeds on Nick or Ricky personally... but then i'd do that just to stir them up too.. ;)

#include <std_disclaimer>


Any comments made are personal opinion and do not reflect directly on the position my current or past employers may have.

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