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Event ID 20 — NLB Port Rules Configuration

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Applies To: Windows Server 2008

In a Network Load Balancing (NLB) cluster, port rules are configured to control how each port's cluster network traffic is handled. The NLB cluster may fail to converge unless each port rule has a unique host priority (a number between 1 and 32), the port rules are consistent on all cluster hosts, you are using the proper number of port rules, and the virtual IP address is specified in a valid IPv4 or IPv6 address format.

 

Event Details

Product: Windows Operating System
ID: 20
Source: Microsoft-Windows-NLB
Version: 6.0
Symbolic Name: MSG_ERROR_SINGLE_DUP
Message: NLB cluster [%2]: NLB failed to converge due to port rules with a duplicate single host priority %5 in the cluster. Each single host port rule in the NLB cluster must have a unique priority. Please check the NLB configuration of all port rules and make sure that each has a unique host priority (a number between 1 and 32).

Resolve

Check uniqueness of host priorities in port rules

When single host filtering mode is used, traffic to the port or ports governed by that port rule is handled exclusively by the host whose priority has the lowest numeric value. When the host's single host priority is identical to the single host priority of another host, the cluster will not converge until the problem is corrected. You should check the NLB configuration of all port rules and make sure that each has a unique host priority (a number between 1 and 32).

When you are using Network Load Balancing (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.

To check that each port rule has a unique host priority:

  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. If NLB Manager does not already list the cluster, connect to the cluster.
  3. Right-click the cluster, and then click Cluster Properties.
  4. Click the Port Rules tab. In the Defined port rules list, review each port rule to make sure that each has a unique host identifier.
  5. If there are port rules with identical host identifiers, right-click the host for which you want to reconfigure the host identifier, and then click Host Properties.
  6. Click the Host Parameters tab, and in Priority (unique host identifier), specify a value between 1 and 32.

 

Verify

You can verify that the port rules configuration is correct by first checking that a specific port is operating properly, and then checking that all Network Load Balancing (NLB) hosts are in a converged state.

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.

Verify that a specific port rule is operating properly

To verify that a specific port rule is operating properly:

  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 queryportport. Specify the port rule by using a port number that is within the range of the port rule that you want to query.

Verify that all NLB hosts are in the converged state

To verify that all 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 Port Rules Configuration

NLB Cluster