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Event ID 19 — NLB Connection Tracking and Load Balancing

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Applies To: Windows Server 2008 R2

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: 19
Source: Microsoft-Windows-NLB
Version: 6.1
Symbolic Name: MSG_WARN_DESCRIPTORS
Message: NLB cluster [%2]: The maximum number of actively serviced connections that could be tracked by NLB is reached. Although NLB will still accept new connections, it will not track the connection state until other connections are closed. This might result in breaking the affinity maintained by the driver during the connection. To resolve this issue, add more hosts to the cluster and/or increase the %3 value under the HKLM\SYSTEM\CurrentControlSet\Services\WLBS\Parameters\Interface\{GUID} key in the registry.

Resolve

Address NLB connection tracking limits

The maximum number of active connections that Network Load Balancing (NLB) can track is reached. Although NLB will continue to accept new connections, it will not track the connection state until other connections are closed. This might result in breaking the affinity maintained by the driver during the connection.

To address the connection tracking limits, you can either add more hosts to the NLB cluster, which distributes the number of incoming connections across more cluster hosts, or increase the connection tracking limit.

When you are using NLB Manager, 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 Manager 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.

Add a host to the NLB cluster

To add a host to the NLB cluster:

  1. Click Start, click Administrative Tools, and then click Network Load Balancing Manager. You can also open NLB Manager by typing Nlbmgr at a command prompt.
  2. Right-click the cluster where you want to add the host and choose Add Host To Cluster. If NLB Manager does not list the cluster, connect to the cluster.
  3. Type the host's name and click Connect. The network adapters that are available on the host will be listed at the bottom of the dialog box.
  4. Click the network adapter that you want to use for NLB, and then click Next. The IP address configured on this network adapter will be the dedicated IP address for this host.
  5. Configure the remaining host parameters as appropriate, and then click Finish.

Incorrectly editing the registry may severely damage your system. Before making changes to the registry, you should back up any valued data on your computer.

Increase the connection tracking limit by editing the registry key

To increase the connection tracking limit by editing the registry key:

  1. Open Registry Editor.

  2. Edit the value in the HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\WLBS\Parameters\Interface\{GUID}\MaxDescriptorAllocs.

    The GUID is the globally unique identifier of the network adapter that is experiencing the problem. This is the network adapter that is bound to NLB. If NLB is, or has been, bound to multiple network adapters, you can find the correct adapter by looking at the value for the ClusterIPAddress key for each GUID entry in the registry.

  3. You should double the existing value of the registry key. After increasing the value, you must disable and re-enable the appropriate network adapter.

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