DNR Sorts IP Address for Multihomed Hosts Before Returning List

• Microsoft Windows NT Workstation version 4.0
• Microsoft Windows NT Server version 4.0
• Microsoft Windows 95

SYMPTOMS

When a Windows sockets client application connects to a server application on a multihomed server, it may not connect to the "nearest" or "best" IP address on that server.

CAUSE

When a Windows sockets application is used to connect to another computer, it normally calls gethostbyname() to obtain the IP address of the target computer. This Winsock API invokes the Domain Name Resolver (DNR) component on the client computer to send a name query to a Domain Name Service (DNS) server. DNS returns a list of IP addresses to the DNR, which places the list into a structure and returns it to the application. Most applications then try to connect to the first IP address in the list.

An updated version of the DNR is now available. This version of the DNR sorts the list of IP addresses into the "best" order by examining the route table of the computer on which it is running. For instance, If any of the IP addresses in the list returned by the DNR are on a common subnet with the client, that IP address will be moved to the top of the list. This enhancement allows the client application to make the most direct connection possible to the server.

RESOLUTION

To resolve this problem, obtain the following fix or wait for the next Windows NT service pack.

This fix should have the following time stamp:

   03/11/98  05:56p   42,768 Rnr20.dll (Intel)
   03/11/98  05:52p   70,416 Rnr20.dll (Alpha)

STATUS

Windows NT 4.0

Microsoft has confirmed this to be a problem in Windows NT version 4.0. A supported fix is now available, but has not been fully regression tested and should be applied only to systems experiencing this specific problem. Unless you are severely impacted by this specific problem, Microsoft recommends that you wait for the next Service Pack that contains this fix. Contact Microsoft Technical Support for more information.

Windows 95

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