I am wrestling with deploying an application on Windows Server 2012. The problem is that after accepting about ~2000 TCP connections it fails to accept more. And I need much more. We have 8 cores, 16 GB RAM, 3GH CPU, pretty strong box. But not capable of holding more than 2000 socket connections..

The questions:

  1. if this is some kind of server OS limitation, can it be lifted?
  2. could anyone recommend tools for benchmarking how many TCP connections the server is capable of?
  • After some investigation I've figured that the limitation was actually imposed by the hosting company, their firewall wasn't allowing more than 2k concurrent TCP connections. – Dima Jun 27 '14 at 17:24
  • sure it's not a CAL qty issue? – Jim Michaels Sep 1 '16 at 13:30
  • @Jim - yep, pretty sure, after we lifted the limitation with hosting vendor, the number of accepted connections gets to 10k. – Dima Sep 1 '16 at 17:33

I hate replying to questions with links however I read through this very recently and found it hugely interesting so thought you might appreciate the read:



  • Thanks! Very useful tools indeed. I've tried it and it confirms my own tests. That server won't accept more than 2000 TCP connections. Now I need to figure out why? – Dima May 22 '14 at 18:17
  • It could be port exhaustion due to TIME_WAIT, though that sounds unlikely. It could be lack of ephemeral ports due to MaxUserPort setting, though again, 2000 is very low. You could try my TIME_WAIT perfmon counter download to monitor TIME_WAIT states (it also shows MaxUserPort, though you can easily check that in the registry). See here: lenholgate.com/blog/2014/04/time-wait-perfmon-counters.html for the tool. – Len Holgate Jun 27 '14 at 21:06

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