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Event ID 81 — NLB Connection Tracking and Load Balancing

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Applies To: Windows Server 2008

The Network Load Balancing (NLB) driver on the host tracks connections to maintain client/network affinity configured on the NLB cluster. If the driver is not functioning properly, NLB may not be able to track TCP connections or may experience load distribution errors.

 

Event Details

Product: Windows Operating System
ID: 81
Source: Microsoft-Windows-NLB
Version: 6.0
Symbolic Name: MSG_WARN_TCP_CALLBACK_OPEN_FAILED
Message: NLB cluster [%2]: NLB can't track TCP connections because it was unable to open the TCP connection callback object. Although NLB will still accept new connections, it will not track the connection state until this is resolved. This might result in breaking the affinity maintained by the driver during the connection. To resolve this issue, try to unbind then rebind NLB to the adapters.

Resolve

Disable and enable NLB network adapters

If Network Load Balancing (NLB) is unable to open a TCP connection callback object, then NLB cannot track TCP connections. Although NLB will still accept new connections, it will not track the connection state, which may cause the affinity that is maintained by the driver during the connection to break. You should disable and re-enable the network adapter before attempting to bind NLB to the adapter again.

Membership in the local Administrators group, or equivalent, is the minimum required to complete this procedure.

To disable and re-enable all network adapters:

  1. Click Start, click Network, and then click Network and Sharing Center
  2. Under Tasks, click Manage network connections.
  3. Right-click the network adapter you want to disable, and click Disable. If you are prompted for an administrator password or confirmation, type the password or provide confirmation.
  4. Right-click the network adapter you want to enable, and click Enable. If you are prompted for an administrator password or confirmation, type the password or provide confirmation.

Verify

When you are using nlb.exe, you must be a member of the Administrators group on the host that you are configuring, or you must have been delegated the appropriate authority. If you are configuring a cluster or host by running nlb.exe from a computer that is not part of the cluster, you do not have to be a member of the Administrators group on that computer.

To verify that all Network Load Balancing (NLB) hosts are in the converged state:

  1. Open an elevated Command Prompt window. Click Start, point to All Programs, click Accessories, right-click Command Prompt, and then click Run as administrator.
  2. Type nlb.exe query, which displays the current cluster state and the list of host priorities for the current hosts of the cluster.
  3. Confirm that all hosts display converged as their current state.

 

 

 

NLB Connection Tracking and Load Balancing

NLB Cluster