microsoft inbound connection limit nazi says: no connection for you!

So, I put together a Win32 binary release of AOLserver 4 and decided to do some benchmarking on my Dell C840 laptop running WinXP Home.

To my surprise, I discovered that Microsoft has imposed an Inbound Connections Limit in Windows XP! Of course, this is nothing new — Microsoft introduced this back in 1996 or thereabouts with the release of Windows NT 4.0 Workstation. I found a good article by Tim O’Reilly about it. In his article, he indicates that only inbound connections on “reserved ports” (those below 1024) are supposed to be limited, but my tests on WinXP Home show that even port 8000 is being limited.

In these Microsoft KB articles it seems that the limit may be controlled by a registry setting:

Check to see if the server was configured by upgrading a computer running Windows NT Workstation to Windows NT Server. If it was, the following registry parameter may need to be increased from a hex value of 0xa (10) to 0xFFFFFFFF:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\LanManServer\Parameters\Users

However, twiddling that setting doesn’t seem to make any difference — I bet the value is baked into one of the DLLs that the non-Server versions ship with.

So, the bad news is that unless you’re running one of the “Server” versions of Windows, your going to be hurt by this foolish inbound connection limit. This means that running a web server on your non-Server machine may flake out if your application that you’re developing initiates many requests quickly — things like Web Services-like traffic in an IFRAME or hidden DIV come to mind.

Perhaps Microsoft could release a “WinXP Developer” edition that’s the same price and feature set as WinXP Professional but without the connection limit. Production servers should still use the Server edition, but at least this way folks can do development and testing without paying the ridiculous cost of a Server license for their desktop machine!