On a recent Windows 2008 R2 server I was working on, the client complained about FTP connections timing out.  Here are my findings and the fix (credit to this post which is where I found the answer)!

Large (i.e. 1 MB+) FTP uploads from newer client Windows OSes such as Windows Vista or Windows  7 running the FileZilla client (3.3.3) in passive mode, connecting to a Windows 2008 server would slow down, then hang/stall after a few seconds, eventually timing out.  In testing I found the issue occurred in both IIS/MS FTP/Microsoft FTP or FileZilla server running on the 2008 R2 box.  Here’s an example… on a Windows 7 FileZilla client, the transfer would hang at the EXACT same place EVERY time (in my case it hung exactly at 458,752 bytes):

Using a Mac or Windows XP FileZilla client did not produce a problem and the transfer always worked perfectly.

The solution was simple.  Enter this command line (must be run as admin) to disable the TCP autotuning mechanism on the server:

netsh int tcp set global autotuninglevel=disabled

Problem solved!  Big transfers – full speed ahead!  NOTE: I’m pretty sure this can be used on the client versus the server to work around the issue as well… please let me know in the comments.

Environment:

Server OS: Windows 2008 R2 Server
Client OS: Windows 7
FTP Server: IIS / MS FTP or FileZilla
FTP Client: FileZilla for Windows