Microsoft KB Archive/253468

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Two Network Adapters Are Required for Winsock Proxy Server

Article ID: 253468

Article Last Modified on 2/4/2002


  • Microsoft Proxy Server 1.0 Standard Edition
  • Microsoft Proxy Server 2.0 Standard Edition
  • Microsoft Internet Security and Acceleration Server 2000 Standard Edition

This article was previously published under Q253468


When you try to use a Winsock-based program to connect to a remote host from "behind" the Proxy Server-based computer, you may be unable to do so, but connections using the Web Proxy service are not affected. Only client applications dependent upon ISA's Firewall Service and Proxy Server's Winsock Proxy Service are affected by this issue.


This issue can occur if your ISA or Proxy Server computer only contains 1 network adapter. When a client "behind" the Proxy Server-based computer initiates a Winsock-based network connection, the client computer must determine if the destination is local or remote. When the destination is local, it passes the connection request to the default Winsock dynamic link library (.dll) file, and permits the connection to proceed unmodified. If the Firewall or Winsock Proxy service determines that the connection is remote, it uses the remote Winsock protocol to send (or remote) the connection request.

If the Proxy Server is configured with a single network adapter, the destination will appear to be local to the client computer. Because of this, the client will then send an unmodified Winsock request which will not work at the Proxy Server.


To work around this issue, install a second network adapter on the Proxy Server-based computer.

NOTE: This second adapter can be a network adapter or a modem.

Keywords: kbnetwork kbprb KB253468