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Which is the default TCP connect timeout in Windows? There is a registry key to configure it or it's set dynamically?

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2 Answers 2

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In Windows the value is dynamic for established conections, though the default for initial connections is 72 seconds. The Registry settings are defined in this article:

http://technet.microsoft.com/en-us/library/cc739819(WS.10).aspx

HKEY_LOCAL_MACHINE \SYSTEM \CurrentControlSet \Services: \Tcpip \Parameters

TcpInitialRTT: Defines what the initial time-out settings are for new connections. This number in seconds is doubled each time it retransmits before timing a connection out. Defaults to 3.

TcpMaxConnectRetransmissions: Defines the number of retransmissions before timing a connection out. Defaults to 5.

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One only need to re-establish a given connection after changing these, no need to reboot, right? Do you possibly know which one should be changed to stop Windows 7 from proactively dropping existing connections on short outages? I've tried changing TcpMaxDataRetransmissions to 16 (default is supposed to be 5), but my PuTTY still drops the connections really fast on brief outages, whereas ssh on OS X and same network keeps them just fine. superuser.com/questions/529511/… –  cnst Jan 8 '13 at 20:09
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Actually, it worked after I've rebooted! Nothing ever changes in Windows! Seems like you have to reboot, and the setting has no effect on either old or new connections if you simply edit the registry without rebooting! –  cnst Jan 8 '13 at 22:14

TcpInitialRTT and TcpMaxConnectRetransmissions may not be present in Vista and Windows 2008. This Microsoft document does not include them. http://download.microsoft.com/download/c/2/6/c26893a6-46c7-4b5c-b287-830216597340/TCPIP_Reg.doc

And this says at least TcpInitialRTT is gone, although I don't know how reliable it is. http://pul.se/Blog-Post-TCP-IP-Stack-hardening-in-Operating-Systems-starting-with-Windows-Vista_SharePoint-kHPTTCP0WJ5,7zq00hH0wINE

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