Microsoft KB Archive/253253

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Proxy: WSP Clients Cannot Reach Remote Segments of the LAN

Article ID: 253253

Article Last Modified on 11/1/2006


  • Microsoft Windows NT Server 4.0 Standard Edition
  • Microsoft Proxy Server 1.0 Standard Edition
  • Microsoft Proxy Server 2.0 Standard Edition

This article was previously published under Q253253


Local area network (LAN) clients that are using the Winsock Proxy (WSP) client may be unable to reach certain segments of the the LAN if those segments are separated by a router and on a logically different TCP/IP Network ID.

For example, this behavior may occur if one office is connected to another office (possibly across town) with a router and one or both offices may have its own independent Proxy servers for Internet connectivity. Or, a second office may have been added to the network after the Proxy server was initially set up.

Even though the router provides IP routing, clients that are configured to access the Internet by using a Winsock proxy through the Proxy server may not be able to connect to computers on the LAN across their router.


This behavior can occur if the local address table (LAT) on the Proxy server does not include the remote LAN's IP address range or Network ID.

The WSP client program consults the local copy of the LAT to make decisions about routing the IP packets. If the destination is in the LAT, it lets them pass through. If the destination is not in the LAT, the WSP client intercepts it, repackages it in the WSP protocol, and forwards it to the Proxy server to be transmitted to the internet.

Note that only Winsock Proxy requests consult the (LAT) to determine which route to take.


To resolve this issue, add the network address ranges that are in use on all the LANs you need to gain access to without going through the Proxy server. (By definition, this information is what constitutes the LAT.)

You can add to or change the LAT on the Proxy server by clicking Start, pointing to Programs, clicking Proxy Administration, clicking Winsock or Web Proxy Service, clicking the Service tab, and then clicking Local Address Table.

Clients receive a copy of the LAT at the next restart, or you can force a new copy by clicking Update Now in the WSP Client tool in Control Panel on the client computers.

Keywords: kbenv kbprb KB253253