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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?

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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. – Mystere Man Jun 6 '09 at 18:01
I am referring to the 10 half-open connection limit. – RedFilter Jun 6 '09 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 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 at 15:30
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4 Answers

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From the base OS perspective, the limit has gone.

With Vista pre-sp2 it depended on the version. See http://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.

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Thanks, but interested in Windows 7, not Vista. – RedFilter Jun 6 '09 at 14:31
Sorry, I'll update. – Peter Stuer Jun 6 '09 at 15:24
Thanks, the last link was particularily helpful. – RedFilter Jun 6 '09 at 20:24
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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. – jvenema Nov 23 '11 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. – Peter Stuer Mar 6 at 11:31
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up vote 4 down vote

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.

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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 '10 at 13:54
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up vote 1 down vote

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.

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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. – Mystere Man Jun 6 '09 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 '09 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 '09 at 19:58
You deduced correctly. thanks for the link splattne, sounds like the limit is still there :( – RedFilter Jun 6 '09 at 20:02
I confirmed with this tool that on Windows 7 the limit is still 10. – RedFilter Jun 6 '09 at 20:11
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up vote 0 down vote

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

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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 '09 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 '09 at 15:06
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