Possible Network File Damage with Redirector Caching (148367)

IMPORTANT: This article contains information about modifying the registry. Before you modify the registry, make sure to back it up and make sure that you understand how to restore the registry if a problem occurs. For information about how to back up, restore, and edit the registry, click the following article number to view the article in the Microsoft Knowledge Base:

256986 Description of the Microsoft Windows Registry

SYMPTOMS

When you use the Microsoft Client for Microsoft Networks, a file on a Microsoft networking server (such as a Microsoft Windows NT, Windows 95, Microsoft Windows for Workgroups, or Microsoft LAN Manager server) may become damaged or may contain invalid data if multiple workstations access the file at the same time.

CAUSE

The network redirector (Vredir.vxd) caches data locally for files it accesses on a Microsoft networking server. If the file size does not change or if the last modified time does not change within a two-second period, the redirector reads file data from the locally stored cache rather than from the file on the server.

RESOLUTION

WARNING: If you use Registry Editor incorrectly, you may cause serious problems that may require you to reinstall your operating system. Microsoft cannot guarantee that you can solve problems that result from using Registry Editor incorrectly. Use Registry Editor at your own risk.

This issue is resolved by the following updated file for Windows 95:

   VREDIR.VXD version 4.00.1112 (dated 2/11/97) and later

The following file is available for download from the Microsoft Download Center:

Download Vredrupd.exe now

For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base:

119591 How to Obtain Microsoft Support Files from Online Services

Microsoft scanned this file for viruses. Microsoft used the most current virus-detection software that was available on the date that the file was posted. The file is stored on security-enhanced servers that help to prevent any unauthorized changes to the file.

This update resolves this issue by disabling caching on all FileOpen calls only if the following binary value is present in the registry:

HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\VREDIR

Value Name: DiscardCacheOnOpen
Value: 01 00 00 00

If this value is not present or is set to 0, this update behaves the same as Vredir.vxd versions 4.00.955 and earlier.

This value is not added by default and must be added manually in order to disable caching when opening files.

MORE INFORMATION

For additional information about issues resolved by updates to this component, please see the following articles in the Microsoft Knowledge Base:

172594 Cannot Connect to Server with 15 Characters and Period in Name

165402 Windows 95 Update to Encrypt Passwords in Memory

161100 File May Be Truncated When Copied to a Full Network Drive

157114 "Access Denied" Attempting to Run File on LM/X Server

152186 Possible Network Data Corruption If Locking Not Used

142803 Hang or Locking Error Accessing Database Files Over Network

140558 Deleting Files on Samba Servers May Delete Local Files Instead

138249 Updated Vredir.vxd Corrects Errors Running Files on LMX

160807 Cannot Connect to Windows NT Server with Many Shares

150215 Disabling Automatic Network Shortcut Resolution

138014 File May Be Truncated to Zero Bytes When Copied Onto Itself

136834 Error Copying Read-Only Files to Core SMB Server