SMC Elite Ultra NIC Causes UNIX Computers to Disconnect TCP/IP

• Microsoft Windows NT Workstation versions 3.5 and 3.51
• Microsoft Windows NT Server versions 3.5 and 3.51
• Microsoft TCP/IP-32 for Windows for Workgroups, versions 3.11, 3.11a, and 3.11b

SYMPTOMS

TCP/IP connections between two UNIX computers or between a Microsoft network computer and UNIX computer are lost.

This happens on a network with both UNIX computers and a computer running a Microsoft protected mode TCP/IP protocol stack (including TCP/IP-32 versions 3.11, 3.11a, and 3.11b and Windows NT versions 3.5 and 3.51) and where the Microsoft network computer is using the SMC Elite Ultra network interface card (NIC).

CAUSE

The SMC Elite Ultra NIC incorrectly passes up ethernet packets addressed to other computers. This causes the Microsoft TCP/IP protocol stack to send an ICMP Host Unreachable message back to the source computer. Some UNIX TCP/IP stacks disconnect when they receive this ICMP packet.

WORK AROUND

To work around the SMC hardware problem, Microsoft has removed the code from the protected mode TCP/IP stack which sends the ICMP Host Unreachable message under these circumstances.

Versions of the Windows NT version 3.51 file, TCPIP.SYS, date stamped 6/14/95 or later incorporate the above workaround.

Versions of the Windows for Workgroups TCP/IP-32 file, VIP.386, date stamped 7/19/95 or later incorporate the above workaround.

This workaround is also included in the release version of Windows 95.

STATUS

Microsoft has confirmed this to be a problem while using Windows NT versions 3.5 and 3.51 and Windows for Workgroups TCP/IP-32 versions 3.11, 3.11a, and 3.11b.

Windows NT 3.51

This problem has been corrected in the latest U.S. Service Pack for Windows NT version 3.51. For information on obtaining the Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):

    S E R V P A C K

Windows NT 3.5 and TCP/IP-32 3.11x

A workaround to this problem is in development, but has not been regression- tested and may be destabilizing in production environments. Microsoft does not recommend implementing this workaround at this time. This workaround is available from Microsoft Product Support Services as well as electronically by "anonymous" ftp at:

   ftp://ftp.microsoft.com:/bussys/winnt/winnt-unsup-ed/fixes/nt35/icmpfix

   -and-

   ftp://ftp.microsoft.com:/bussys/clients/wfw/tcpip32-fixes/icmpfix