My current development machine is Windows XP, and I use a modified tcpip.sys to allow me to exceed the 10 connection limit built in to IIS. I know that Vista's IIS has the same limit.

Can anyone confirm whether this connection limit is present in Windows 7 IIS as well?

  • Are your eferring to the 10 authenticated connection limit in XP, or the 10 half-open connections limit? It seems that those answering your question are assuming the latter.. which doesn't make a lot of sense regarding IIS on desktop OS's. Jun 6, 2009 at 18:01
  • I am referring to the 10 half-open connection limit.
    – RedFilter
    Jun 6, 2009 at 19:56
  • This question is badly-formed. The (outbound) half-open connection limit from Windows XP SP2 has nothing to do with the (inbound) IIS number-of-requests limit. The accepted answer covers both possibilities, but the question is like asking "what orange is the best pear?"
    – TristanK
    Mar 6, 2012 at 22:47
  • @TristanK I framed the question as best as I could with my limited understanding. The issue I was trying to deal with was the IIS connection limit exceeded errors (actually EventID 4226) that you can get when hosting IIS on Windows XP. The reason I assumed half-open connections were the issue was that this is what was patched by the TCPIP.SYS patcher I used (lvllord.de/?lang=en&url=4226patch/faq), which resolved the issue.
    – RedFilter
    Mar 7, 2012 at 15:30

5 Answers 5


From the base OS perspective, the limit has gone.

With Vista pre-sp2 it depended on the version. See https://stackoverflow.com/questions/413110/which-is-the-maximum-number-of-windows-concurrent-tcp-ip-connections/929973#929973

Since Vista SP2 the limitation have been removed from TCPIP.SYS, and has been configurable through a registry key. Windows7 should follow that same behavior (source and for 7, and here), but of course we will not know for 7 definitely until RTM since appart from technial there may be license restrictions.

However, IIS introduces its own limitations, depending on the version of the OS. For Windows 7 this limit is between 3 (Home Premium) and 10 (Business, Enterprise & Ultimate) simultaneous connections . Depending on your scenario, it might help to lower the connection timeout to free up slots sooner.

  • Thanks, but interested in Windows 7, not Vista.
    – RedFilter
    Jun 6, 2009 at 14:31
  • Sorry, I'll update. Jun 6, 2009 at 15:24
  • 1
    This answer describes TCP connections, but does not discuss IIS itself. IIS has a 10-connection limit in any non-server OS. Easily confirmed by testing. Nov 23, 2011 at 13:55
  • You are right, I included the info in the answer. For Windows 7, it is not always 10. For "Home Premium" edition the limit is 3. Mar 6, 2012 at 11:31

The connection limit in IIS is NOT THE SAME as the 10 half-port open limit. This is a limit built into IIS and has nothing to do with TCP/IP. Pay for server or run Apache.

  • No need to pay for a server, as I was having no issue with connection limit - only half-open connection limit, which is a solved problem.
    – RedFilter
    Apr 21, 2010 at 13:54

There is a special version of TCP-Z, a tool for "patching" tcpip.sys, for Windows 7 - an indication that this setting still exists in Microsoft new operating system.

Disclaimer: it is not advised to change operating system drivers.

  • You're confusing the "10 connection limit" of Desktop OS's with the "10 half-open connection limit" that was imposed as a security restriction. I'm not sure which the question asker was referring to. The "10 connection limit" is imposed on authenticated connections to prevent Desktop IIS from being used as a server. Jun 6, 2009 at 18:00
  • The question itself is a little confusing. The asked writes "IIS connection limit" (?) and "patching tcpip.sys", so I deduced he was referring to this limit.
    – splattne
    Jun 6, 2009 at 18:59
  • I am referring to the 10 half-open connection limit. The same limit that was fixed by this Win XP patch: lvllord.de/?url=tools.
    – RedFilter
    Jun 6, 2009 at 19:58
  • You deduced correctly. thanks for the link splattne, sounds like the limit is still there :(
    – RedFilter
    Jun 6, 2009 at 20:02
  • I confirmed with this tool that on Windows 7 the limit is still 10.
    – RedFilter
    Jun 6, 2009 at 20:11

Edit: I stand corrected, there is a 10 concurrent connection HTTP limit, confirmed by testing.

  • What is the basis for your statement that there is no concurrent connection limit in Windows 7 IIS? Is it an assumption based on your knowledge of Vista, or have you confirmed it to be the case?
    – RedFilter
    Jun 6, 2009 at 14:18
  • My original screenshot was against IIS7 server, not IIS 7.5 client due to a typo in hostname. Apologies.
    – JohnW
    Jun 6, 2009 at 15:06

Pleae see this link, and how to get more concurrent connections in IIS.



  • 1
    Welcome to Server Fault! Generally we like answers on the site to be able to stand on their own - Links are great, but if that link ever breaks the answer should have enough information to still be helpful. Please consider editing your answer to include more detail. See the FAQ for more info.
    – slm
    Apr 3, 2013 at 20:15
  • -1: The information in the linked article is incorrect.
    – RedFilter
    Apr 3, 2013 at 21:03

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