DOCUMENT:Q111670 08-AUG-2001 [winnt] TITLE :ArpCacheSize Defaults to 62 Entries PRODUCT :Microsoft Windows NT PROD/VER:3.1 OPER/SYS: KEYWORDS:kbenv ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Windows NT Advanced Server, version 3.1 ------------------------------------------------------------------------------- SYMPTOMS ======== A Windows NT server may not be able to maintain reliable connections to a large number of active TCP/IP clients. CAUSE ===== The default ArpCacheSize is set to 62 entries. The ArpCache maintains a mapping between IP and machine addresses, so the size should be adjusted to accommodate the number of active clients. Otherwise the oldest entries will be purged and then address resolution protocol (ARP) will be used to re- obtain the mappings when they're needed. RESOLUTION ========== NOTE: This resolution only applies to Windows NT version 3.1. In Windows NT 3.5 and 3.51, the ArpCacheSize is dynamic and the registry parameter does not exist anymore. You can adjust the ArpCacheSize in Windows NT 3.1 by using the following procedure: WARNING: Using Registry Editor incorrectly can cause serious, system-wide problems that may require you to reinstall Windows NT to correct them. Microsoft cannot guarantee that any problems resulting from the use of Registry Editor can be solved. Use this tool at your own risk. 1. Start Registry Editor. 2. Select the HKEY_LOCAL_MACHINE on Local Machine window. 3. Go to the SYSTEM\CurrentControlSet\Services\tcpip\parameters key. 4. Create a new value of type REG_DWORD named ArpCacheSize. 5. Set it for the highest number of clients that is likely to be active at one time. Additional query words: prodnt ====================================================================== Keywords : kbenv Technology : kbWinNTsearch kbWinNTAdvSerSearch kbWinNTAdvServ310 kbWinNT310Search Version : 3.1 ============================================================================= 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.