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Windows 95 Stops Responding Because of Land Attack

Retired KB ArticleThis article was written about products for which Microsoft no longer offers support. Therefore, this article is offered "as is" and will no longer be updated.
View products that this article applies to.
Article ID:177539
Last Review:November 15, 2006
Revision:2.4
This article was previously published under Q177539
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SYMPTOMS

After receiving spoofed connection request (SYN) packets over TCP/IP, a computer running Windows 95 may begin to operate slowly. After about one minute, Windows returns to normal operation.

This problem may occur with TCP/IP on other operating systems as well.

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CAUSE

This behavior occurs due to "Land Attack." Land Attack sends SYN packets with the same source and destination IP addresses and the same source and destination ports to a host computer. This makes it appear as if the host computer sent the packets to itself. Windows 95 operates more slowly while the host computer tries to respond to itself.

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RESOLUTION

Without WinSock 2.0 Update

This issue is resolved by the following updated file for Windows 95 and Windows 95 OEM Service Release 2 (OSR2) without the WinSock 2.0 update only: 
   Vtcp.386 version 4.00.956 (dated 11/26/97) and later
To install this update, follow these steps:
1.Download the Vtcpup11.exe file from the Microsoft Download Center to an empty folder on your hard disk..
2.In My Computer or Windows Explorer, double-click the Vtcpup11.exe file you downloaded in step 1.
3.Follow the instructions on the screen.
The following file is available for download from the Microsoft Download Center:
Download Vtcpup11.exe now (http://download.microsoft.com/download/win95upg/tcpip/1/w95/en-us/vtcpup11.exe)
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 (http://support.microsoft.com/kb/119591/EN-US/) 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.

The following files are installed by Vtcpup11.exe: 
   File name     Version    Date/Time        Size     Destination folder
   ----------------------------------------------------------------------
   Vtcp.386      4.00.956   11/26/97 9:56a   47,413   Windows\System

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With WinSock 2.0 Update

This issue is resolved by the following updated file for Windows 95 and Windows 95 OEM Service Release 2 with the Winsock 2 update only: 
   Vtcp.386 version 4.00.1424 (dated 12/10/97) and later
To install this update, follow these steps:
1.Download the Vtcpup20.exe file from the Microsoft Download Center to an empty folder.
2.In My Computer or Windows Explorer, double-click the Vtcpup20.exe file you downloaded in step 1.
3.Follow the instructions on the screen.
The following file is available for download from the Microsoft Download Center:
Download vtcpup20.exe now (http://download.microsoft.com/download/win95upg/update4/1/w95/en-us/vtcpup20.exe)
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 (http://support.microsoft.com/kb/119591/EN-US/) 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 secure servers that prevent any unauthorized changes to the file.

The following files are installed by Vtcpup20.exe: 
   File name     Version    Date/Time        Size     Destination folder
   ---------------------------------------------------------------------
   VTCP.386      4.00.1424  12/10/97  2:24p  52,133   Windows\SYSTEM

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Identifying the Winsock 2.0 update

For information about how to determine whether the Winsock 2.0 update has been installed an a computer running Windows 95, please see the following article in the Microsoft Knowledge Base:
177719 (http://support.microsoft.com/kb/177719/EN-US/) Identifying Windows Sockets 2 Run-Time Components for Windows 95

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MORE INFORMATION

For additional information about this issue as it applies to Microsoft Windows NT, please see the following article in the Microsoft Knowledge Base:
165005 (http://support.microsoft.com/kb/165005/EN-US/) Windows NT Slows Down Because of Land Attack


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

170791 (http://support.microsoft.com/kb/170791/EN-US/) Windows 95 TCP Clients Run Out of Ports
168747 (http://support.microsoft.com/kb/168747/EN-US/) Update to Windows 95 TCP/IP to Address Out-of-Band Issue

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APPLIES TO
•Microsoft Windows 95

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Keywords: 
kbhotfixserver kbqfe kbdownload kbfix kbgraphxlinkcritical kbnetwork KB177539

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