Loopback Send/Receive Over IPX/SPX May Not Work Under Stress

• Microsoft Windows 95

SYMPTOMS

In Windows 95, the IPX/SPX-compatible protocol (NWLINK) may not successfully send and receive data under the following conditions:

• The same computer is both the sender and receiver of the data.
• A large amount of data is being sent in a continuous stream.
• The network adapter (NDIS) driver does not provide loopback functionality.

• The data transfer never finishes. This is the most common symptom.
• The computer may restart. This occurs rarely, and only if a large block of data is being transferred.
• The computer may stop responding (hang), requiring a cold boot (power- off or reset). This occurs rarely, and only if a large block of data is being transferred.

CAUSE

Loopback packets (in which the source and destination addresses are the same) are not recognized and handled internally by NWLINK. Instead, they are passed to the network adapter driver. If the network adapter driver does not recognize and handle loopback packets, the packet is sent out on the network wire. Under continuous stress of this type, and under certain timing conditions, the symptoms listed above may occur.

STATUS

Microsoft has confirmed this to be a problem in Windows 95. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

RESOLUTION

This condition may occur when you are running a program designed to test data throughput over IPX/SPX (including WinSock over IPX/SPX). We recommend that such tests be conducted between two separate computers, instead of on one computer in loopback mode. This not only avoids the problems mentioned here, but also returns more meaningful results.

You can also work around this problem by using a network adapter driver that handles loopback packets internally without transmitting them on the network medium. For information about whether a particular network adapter driver handles loopback packets internally, contact the vendor of your network adapter.

MORE INFORMATION

For additional information about issues related to loopback operations with NWLINK, please see the following articles in the Microsoft Knowledge Base:

   ARTICLE-ID: Q146107
   TITLE     : Local File Transfer Using UNC Slow with NWLnkIPX

   ARTICLE-ID: Q127054
   TITLE     : Loopback Functionality Does Not Work with Miniport Drivers

   ARTICLE-ID: Q124648
   TITLE     : DC21040 Causes Windows NT 3.5 to Stop Responding (Hang)