Problem: On Windows systems, after network outage, advisors not working in a high availability setup

By default, when the Windows operating system detects a network outage, it clears its address resolution protocol (ARP) cache, including all static entries. After the network is available, the ARP cache is repopulated by ARP requests sent on the network.

With a high availability configuration, both servers take over primary operations when a loss of network connectivity affects one or both. When the ARP request is sent to repopulate the ARP cache, both servers respond, which causes the ARP cache to mark the entry as not valid. Therefore, the advisors are not able to create a socket to the backup servers.

Preventing the Windows operating system from clearing the ARP cache when there is a loss of connectivity solves this problem. Microsoft has published an article that explains how to accomplish this task. This article is on the Microsoft Web site, located in the Microsoft Knowledge Base, article number 239924: http://support.microsoft.com/default.aspx?scid=kb;en-us;239924.

The following is a summary of the steps, described in the Microsoft article, to prevent the system from clearing the ARP cache:
  1. Use the Registry editor (regedit or regedit32) to open the registry.
  2. View the following key in the registry:
    HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Tcpip\Parameters
  3. Add the following registry value: Value Name: DisableDHCPMediaSense Value Type: REG_DWORD.
  4. After the key is added, edit the value and set it to 1.
  5. Reboot the machine for the change to take effect.
Note: This affects the ARP cache regardless of the DHCP setting.


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Last updated: May 14, 2012 02:14 PM EDT
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