Microsoft KB Archive/249647

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IGMP Incorrectly Sends Membership Packets to Several Group Addresses


The information in this article applies to:

  • Microsoft Windows 95
  • Microsoft Windows 95 OEM Service Release, versions 1.0, 2.0, 2.1, 2.5


The Internet Group Membership Protocol (IGMP) implementation in the Windows 95 Winsock 2 update incorrectly attempts to send membership packets to the (All Routers) and (All Hosts) group addresses. This is an unnecessary broadcast that may cause routers to report errors upon the receipt of these IGMP broadcasts.


The Winsock 2 update for Windows 95 updates the Vip.386 file that implements the IGMP protocol. This implementation of the IGMP protocol does not skip these multicast addresses when it is registering group membership.


A supported fix is now available from Microsoft, but it is only intended to correct the problem described in this article and should be applied only to systems experiencing this specific problem.

To resolve this problem, contact Microsoft Product Support Services to obtain the fix. For a complete list of Microsoft Product Support Services phone numbers and information on support costs, please go to the following address on the World Wide Web:

NOTE: In special cases, charges that are normally incurred for support calls may be canceled, if a Microsoft Support Professional determines that a specific update will resolve your problem. Normal support costs will apply to additional support questions and issues that do not qualify for the specific update in question.

The English-language version of this fix should have the following file attributes or later:

   Date       Time     Version     Size     File name
   1/7/2000   3:20pm   4.10.1660   75,885   Vip.386   


Microsoft has confirmed this to be a problem in Windows 95 (all versions) with the Winsock 2 update.


This update should be applied only to Windows 95-based computers that have the Winsock 2 update installed.

With this fix applied, multicast packets for router discovery are still broadcast when the computer first starts up, if the computer is configured to do so. This behavior is by design.

For additional information about problems resolved by this update, click the article number below to view the article in the Microsoft Knowledge Base:

Q174095 IGMP Query Times Out in Windows 95 with Winsock2 Update

For additional information about Windows 95 updates, click the article number below to view the article in the Microsoft Knowledge Base:

Q161020 Implementing Windows 95 Updates

Additional query words: winsock2 w95qfe

Keywords : osr2 win95
Issue type : kbprb
Technology : kbWin95search kbOPKSearch kbWin95 kbWin95OPKOSR25 kbWin95OPKOSR210

Last Reviewed: June 13, 2001
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