DOCUMENT:Q129005 08-AUG-2001 [winnt] TITLE :Sockets Applications Do Not Switch to Second NIC if One PRODUCT :Microsoft Windows NT PROD/VER: OPER/SYS: KEYWORDS: ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Windows NT Server version 3.1 - Microsoft Windows NT Workstation version 3.1 - Microsoft Windows NT Advanced Server, version 3.1 - Microsoft Windows NT Workstation version 3.5 - Microsoft Windows NT Server version 3.5 ------------------------------------------------------------------------------- SUMMARY ======= If a computer running Windows NT has multiple network adapters, each connected to the same physical subnet through additional hardware (such as a switch), sockets applications use only one of the adapters to communicate over the network. In addition, if the intermediate hardware fails, sockets applications do not detect the failure and do not attempt to recover by using another adapter/switch combination. MORE INFORMATION ================ You can use network hardware in parallel configurations to provide fault tolerance. For example, you can put two network adapters in the same computer, connected to the same physical subnet, so that if one adapter fails the other can take over. If you need intermediate hardware, such as a switch, to connect each adapter to the network, you can attach one switch to each adapter, rather than connecting all the adapters to the same switch. This strategy assumes that the applications communicating over the network can detect the failure of one set of network hardware and automatically start using the other one. Unfortunately, many sockets applications do not detect hardware failure, and will not automatically use the other set of hardware. For example, you run the LPR print monitor on a Windows NT print server with two network adapters, each with its own switch. When LPR initializes, it makes sockets calls that complete correctly as long as one of the network adapters is functioning, even if the switch connecting that adapter to the network has failed. LPR has no way to determine if the failure is with the switch, rather than with other hardware on the network. Therefore, LPR has no reason to try the other adapter/switch combination. While LPR is running it can tell when it loses connections with LPD servers, but it does not know why. If also doesn't know to try using another adapter to work around the problem. NOTE: This problem applies to hardware connecting the computer to the network, not to other devices on the network, such as routers. For example, if there are multiple routes from the Windows NT LPR client to an LPD server, and one route fails, TCP/IP will automatically use a different route, and LPR will continue sending its print jobs. Additional query words: 3.10 prodnt ====================================================================== Keywords : Technology : kbWinNTsearch kbWinNTWsearch kbWinNT350search kbWinNTW350 kbWinNTW350search kbWinNTW310 kbWinNTSsearch kbWinNTS350 kbWinNTS310 kbWinNTAdvSerSearch kbWinNTAdvServ310 kbWinNTS350search kbWinNTS310search kbWinNT310Search kbWinNTW310Search ============================================================================= THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. Copyright Microsoft Corporation 2001.