On a Windows 95-based computer with the Winsock2 Update for Windows 95 installed, IGMP queries may time out prematurely. This may result in computers that are members of a multicast group being dropped from group membership.

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The TCP/IP driver in the Winsock2 Update for Windows 95 does not properly implement the Max Response Time field as documented in the IGMP version 2 draft. This behavior may cause clients participating in a multicast group to not respond to IGMP requests from a router within the timeout period. When this occurs, the router no longer forwards multicast packets to the expired group member.

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This issue is resolved by the following updated file for Windows 95 and Windows 95 OEM Service Release 2 (OSR2):

   Vip.386 version 4.10.1512 (dated 7/29/97) and later
				

To install this update, use the following steps.

NOTE: This update should be applied only to Windows 95-based computers on which the Winsock2 Update has been installed.

1.	Download the Vipup20.exe file from the Microsoft Download Center to an empty folder.
2.	In My Computer or Windows Explorer, double-click the Vipup20.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:
For additional information about how to download Microsoft Support files, click the following article number to view the article in the Microsoft Knowledge Base: 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 Vipup20.exe:

   File name     Version    Date/Time        Size     Destination folder
   ---------------------------------------------------------------------
   Vip.386       4.10.1512  7/29/97 3:12p    71,754   Windows\System
				

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The Winsock2 Update for Windows 95 is included in the Winsock2 Software Development Kit (SDK), available from the following location on the Microsoft FTP site: This issue is known to occur with the Vip.386 file version 4.10.1423 included in the Ws295sdk.exe file dated 6/23/97 from the FTP location listed above. Future revisions to this package may not exhibit this symptom.

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