DOCUMENT:Q150577 09-AUG-2001 [winnt] TITLE :ARP Request for Nonlocal Target Hosts on Same Physical Net PRODUCT :Microsoft Windows NT PROD/VER:3.11 3.50 3.51 OPER/SYS: KEYWORDS: ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Windows NT Workstation versions 3.5, 3.51 - Microsoft Windows NT Server versions 3.5, 3.51 - Microsoft TCP/IP-32 for Windows for Workgroups, versions 3.11, 3.11a, 3.11b ------------------------------------------------------------------------------- SUMMARY ======= If multiple logical subnets are present on the same physical network (with no routers between the subnets), communication between hosts from different subnets might not be possible. The packets destined for nonlocal subnets will be sent to the router (if configured for one) or dropped (if no default gateway is present). The Address Resolution Protocol (ARP) is used by the host to find the physical address (MAC address) of a target host. An ARP request packet is broadcast on the local subnet if the target host subnet address matches the host's subnet address. If the subnet addresses do not match, then ARP resolves the MAC addresses for the router. MORE INFORMATION ================ The following information is extracted from a Microsoft whitepaper on TCP/IP. When running multiple logical subnets on the same physical network, the following command can be used to tell IP to treat all subnets as local and to use ARP directly for the destination: route add 0.0.0.0 MASK 0.0.0.0 Thus, packets destined for "non-local" subnets will be transmitted directly onto the local media instead of being sent to a router. In essence, the local interface card can be designated as the default gateway. This might be useful where several class "C" networks are being used on one physical network with no router to the outside world. Additional query words: prodnt ====================================================================== Keywords : Technology : kbWinNTsearch kbWinNTWsearch kbWinNT351search kbWinNT350search kbWinNTW350 kbWinNTW350search kbWinNTW351search kbWinNTW351 kbWinNTSsearch kbWinNTS351 kbWinNTS350 kbWinNTS351search kbWinNTS350search kbAudDeveloper kbTCPIPSearch kbZNotKeyword3 kbTCPIP311 kbTCPIP311a kbTCPIP311b Version : 3.11 3.50 3.51 ============================================================================= 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.