A large file download fails when an ISA Server 2000 SOCKS client computer uses passive mode FTP (923322)


The information in this article applies to:

  • Microsoft Internet Security and Acceleration Server 2004, Standard Edition
  • Microsoft Internet Security and Acceleration Server 2004, Enterprise Edition

SYMPTOMS

When an FTP client computer downloads a large file by using passive mode FTP, the download fails if it takes longer than 120 seconds.

CAUSE

This problem may occur if the following conditions are true:
  • The FTP client computer is configured to use the SOCKS protocol.
  • The FTP client computer uses Microsoft Internet Security and Acceleration (ISA) Server 2004 for outgoing passive FTP access.
  • The idle connection time-out value in ISA Server 2004 is set to the default value of 120 seconds.
Passive mode FTP uses an outgoing control channel connection and an outgoing data channel connection. The file transmission occurs over the data channel. The FTP control channel times out if the following conditions are true:
  • Data is not sent over the control channel during the download operation.
  • A passive mode FTP file download takes longer than 120 seconds.
Then, the FTP server stops the file download operation.

RESOLUTION

To resolve this problem, install the hotfix package that is described in the Knowledge Base article 923330, and then follow the steps that are described in this article. For more information, click the following article number to view the article in the Microsoft Knowledge Base:

923330 Description of the ISA Server 2004 hotfix package: July 27, 2006

After you install this hotfix, run the following Microsoft Visual Basic script to configure the SOCKS filter idle connection time-out value to an appropriate value.

Note To determine the appropriate time-out value, use the following equation: 

Timeout (seconds) = file size / download speed * 1.2

For example, to determine the appropriate time-out value to download a 200-megabyte (MB) file at 1 megabits per second (Mbps), use the following equation: 

 200 / 1 * 1.2 = 240 seconds

You must calculate the value to use individually.

Note The idle connection time-out setting helps free unused resources so that resource-related issues do not occur. Therefore, we recommend that you do not increase the time-out setting unnecessarily. If you use a time-out setting that is less than the default 120 seconds, you can also create unexpected issues.

To change the time-out setting, follow these steps.

Note You must install the KB923330 hotfix package before you can follow these steps.
  1. Click Start, point to All Programs, point to Accessories, and then click Notepad.
  2. Copy and paste the following code into a new Notepad document. Then, save the code to the ISA Server 2004 computer. To do this, use a file name that has a .vbs extension such as SetSocksIdleTimeout.vbs.
    <Script>

''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
'
' Copyright (c) Microsoft Corporation. All rights reserved.
' THIS CODE IS MADE AVAILABLE AS IS, WITHOUT WARRANTY OF ANY KIND. THE ENTIRE
' RISK OF THE USE OR THE RESULTS FROM THE USE OF THIS CODE REMAINS WITH THE
' USER. USE AND REDISTRIBUTION OF THIS CODE, WITH OR WITHOUT MODIFICATION, IS
' HEREBY PERMITTED.
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
' This script sets the idle connection time-out value for the SOCKS filter.
' The value is in seconds.
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''

Sub SetSocksIdleTimeout()

    ' Create the root object.
    Dim root  ' The FPCLib.FPC root object
    Set root = CreateObject("FPC.Root")

    'Declare the other objects needed.
    Dim array       ' An FPCArray object
    Dim Extensions  ' An FPCExtensions object
    Dim ApplicationFilters ' An FPCApplicationFilters object
    Dim ApplicationFilter  ' An FPCApplicationFilter object
    Dim VendorSets  ' An FPCVendorParametersSets collection
    Dim VendorSet   ' An FPCVendorParametersSet object

    ' Get references to the array object
    Set array = root.GetContainingArray

    On Error Resume Next

    Set Extensions = array.Extensions
    CheckError

    Set ApplicationFilters = Extensions.ApplicationFilters
    CheckError

    Set ApplicationFilter = ApplicationFilters.Item("{25765C04-C80B-494C-914E-286297DB8C8E}")

    Set VendorSets = ApplicationFilter.VendorParametersSets
    Set VendorSet = VendorSets.Item( "{25765C04-C80B-494C-914E-286297DB8C8E}" )

    VendorSet.Value("SessionIdleTimeoutSeconds") = 120 ' value in seconds to be set to desired value

    ApplicationFilter.Save false, true

    WScript.Echo "Done..."

End Sub

Sub CheckError()

    If Err.Number <> 0 Then
        WScript.Echo "An error occurred: 0x" & Hex(Err.Number) & " " & Err.Description
        Err.Clear
    End If

End Sub

SetSocksIdleTimeout

</Script>
  3. This script uses the default time-out value of 120 seconds. Change the time-out value to the setting that you want, and then save the script.
  4. Double-click the .vbs file to run the script.
After you run this script, the new time-out value is applied to new SOCKS connections that are made through ISA Server 2004.

To change back to the default time-out value, change the value back to 120 seconds in the script, save the change, and then run the script again.

WORKAROUND

To work around this problem, configure the FTP program to send "keep-alive" commands on the FTP control channel.

For information about whether the FTP program that you use supports this feature, see the documentation for the FTP program.

STATUS

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.
Modification Type:MinorLast Reviewed:9/12/2006
Keywords:kbQFE kbprb KB923322 kbAudITPRO
©2004 Microsoft Corporation. All rights reserved.