FIX: Passive mode FTP client connections never time out when they are connected to IIS 6.0 on a computer that is running Windows Server 2003

On a server that is running Windows Server 2003, the FTP service is installed in Internet Information Services (IIS) 6.0. The FTP clients establish passive mode connections to the FTP server. Some client connections never time out even when no data transfers are in progress.

When this problem occurs to an FTP server that is under a high load condition, new client connections may be refused or existing client connections and data transfers may be dropped.

Notes

• Connection time-outs improve server performance by reducing the number of processing resources that are consumed by idle connections. For more information about how to set connection time-outs, refer to the "More information" section.
• When FTP clients connect to FTP servers to transfer data, the following passive mode connection channels are established:
  • Control channel: This channel is used to send requests and to receive replies.
  • Data channel: This channel is used to transfer file data.
• This issue occurs in a passive mode connection. Specifically, this issue occurs when an FTP command that starts the data transfer is received on the control channel before the data connection channel is established.

Hotfix information

A supported hotfix is available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing the problem described in this article. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.

Prerequisites

You must have the FTP service installed in IIS 6.0 to apply this hotfix. Additionally, the computer must be running Windows Server 2003 Service Pack 1 (SP1) or Windows Server 2003 Service Pack 2 (SP2).

Restart requirement

You must restart the computer if any affected files are being used when you apply this hotfix. To avoid having to restart the computer, stop the FTP Publishing Service service before you apply this hotfix.

Hotfix replacement information

This hotfix does not replace any other hotfixes.

File information

The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.

For all supported x86-based versions of Windows Server 2003 SP1

For all supported x86-based versions of Windows Server 2003 SP2

For all supported x64-based versions of Windows Server 2003 SP1

For all supported x64-based versions of Windows Server 2003 SP2

For all supported IA-64-based versions of Windows Server 2003 SP1

For all supported IA-64-based versions of Windows Server 2003 SP2

To work around this problem, use one of the following methods.

Method 1

Stop and then start the FTP site in IIS Manager.

Method 2

Open IIS Manager. Locate the FTP site, and then open the FTP site properties dialog box. Click the Current Sessions...button to open the FTP User Sessions dialog box, and then manually disconnect the client connections.

Note These workarounds may disconnect active connections while they are transferring data. We recommend that you apply the hotfix to resolve this problem.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

Steps to reproduce the problem

1. On a Windows client computer, open a Command Prompt window.
2. At the command prompt, enter the following directory into the directory field, and then type ftp.exe:
   

   C:\Windows\System32

   
   
   IMPORTANT Because the ftp.exe program does not support FTP passive mode, the following steps use timing-sensitive command sequences. Please make sure that you read through all the steps before you run the test.
3. Run an open <server name> command to open a connection to an FTP server. Then, type the user name and the password to log on to the FTP server.
4. Run a literal pasv command to open a passive mode connection. After you run the command, the FTP server sends you a response. The response includes the IP address and the port number that the FTP client can use to connect to the FTP server.
   
   The following is a sample response:
   
   227 Entering Passive Mode (192,168,1,20,15,61)
   
   
   In this example, "192,168,1,20" is the IP address of the FTP Server, and "15,61" represents the high-order byte and the low-order byte of the port number. In this example, the port number is 3901. The port number is randomly assigned for each passive mode connection.
5. Run a literal list command. Then, immediately open another Command Prompt window, and then type the following command:
   telnet <server name><port number>
   Note Use the port number that was assigned in step 4.
6. On the telnet Command Prompt window, a directory listing is printed. On the FTP Command Prompt window, you receive a response that resembles the following:
   125 Data connection already open; Transfer starting.
7. Keep the two Command Prompt windows open for several minutes. Do not perform any additional actions.
8. Locate the FTP server, and then open IIS Manager. Locate the FTP site, and then open the FTP site properties dialog box. On the FTP Site tab, click Current Sessions... to open the FTP User Sessions dialog box. You notice that this connection is still active.
   
   Note By default, the time-out value for the FTP site connection is 120 seconds.

For more information about how to configure FTP site properties in IIS 6.0, visit the following Microsoft Web site:For more information about how to set connection time-outs in IIS 6.0, visit the following Microsoft Web site:For more information about server-to-server FTP transfers, visit the following Microsoft Web site: