DOCUMENT:Q166750 08-AUG-2001 [winnt] TITLE :ARP Cache Entries May Not Time Out for 10 Minutes PRODUCT :Microsoft Windows NT PROD/VER:winnt:4.0 OPER/SYS: KEYWORDS:kbnetwork ====================================================================== ------------------------------------------------------------------------------- The information in this article applies to: - Microsoft Windows NT Workstation version 4.0 - Microsoft Windows NT Server version 4.0 ------------------------------------------------------------------------------- SYMPTOMS ======== If the media access control address changes for an IP address that a Windows NT computer is communicating with, the Windows NT computer may not be able to communicate to or through the device for up to 10 minutes. CAUSE ===== Windows NT 4.0 offers a configurable ArpCacheLife registry parameter. This parameter controls the arpcache life for entries that are not being referenced in the arpcache. Windows NT computers reference an arpcache entry each time an outbound IP packet is sent to the address described by the entry. Entries being referenced time out after 10 minutes, and this time out value is not adjustable. If you are communicating with a device that has some form of hardware fail-over capability that does not update the arpcache on the other devices on the network, its media access control address may change, and if there is a steady stream of traffic being directed at it by applications on a Windows NT computer, the arpcache entry may not time out for this 10 minute period. RESOLUTION ========== To resolve this problem, either obtain the hotfix mentioned in the STATUS section of this article, or wait for the next Windows NT service pack. NOTE: Service Pack 3 must be applied to Windows NT 4.0 before applying the hotfix. The hotfix should have the following timestamp: (i386) 12/01/97 04:24p 143,632 Tcpip.sys (alpha) 12/01/97 04:21p 263,472 Tcpip.sys STATUS ====== 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. MORE INFORMATION ================ With the hotfix, a new version of Tcpip.sys is available, that allows greater control over arpcache life, as described below: Value: ArpCacheMinReferencedLife Key: Hkey_Local_Machine\System\CurrentControlSet\Services\ \Tcpip\Parameters Value Type: REG_DWORD Valid Range: 0-0xffffffff Default: 600 seconds (10 minutes) Description: ArpCacheMinReferencedLife controls the minimum time that a referenced arpcache entry will expire in. This parameter can be used in combination with the ArpCacheLife parameter, as follows: If ArpCacheLife >= ArpCacheMinReferencedLife, referenced and unreferenced arpcache entries will expire in "ArpCacheLife" seconds. If ArpCacheLife < ArpCacheMinReferencedLife, unreferenced entries will expire in "ArpCacheLife" seconds, and referenced entries will expire in "ArpCacheMinReferencedLife" seconds. For additional information about the ArpCacheLife registry parameter, click the article number below to view the article in the Microsoft Knowledge Base: Q139415 New TCP/IP ArpCacheLife Parameter in Windows NT Additional query words: arp cache proxy MAC resolution protocol ====================================================================== Keywords : kbnetwork Technology : kbWinNTsearch kbWinNTWsearch kbWinNTW400 kbWinNTW400search kbWinNT400search kbWinNTSsearch kbWinNTS400search kbWinNTS400 Version : winnt:4.0 Hardware : ALPHA x86 Issue type : kbbug Solution Type : kbfix ============================================================================= 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.