A computer that is running VMware cannot create a TCP connection to an NFS server that is running Windows Server 2008 or Windows Server 2008 R2

You install Microsoft Services for Network File System (NFS) on a server that is running Windows Server 2008 or Windows Server 2008 R2. When you use this NFS server for VMware virtualization storage, TCP connections from the computers that are running VMware cannot be made to the server.

This issue occurs because a NFS server that is running Windows Server 2008 or Windows Server 2008 R2 supports only 16 TCP connections per IP address. This is by default.

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base: To use a server that is running Windows Server 2008 or Windows Server 2008 R2 in a VMware environment, you must increase the maximum number of TCP connections that are allowed on the server.

To do this, follow these steps:

1. Start Registry Editor. To do this, click Start
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   , type regedit in the Start Search box, and then press ENTER.
   
   
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   If you are prompted for an administrator password or for confirmation, type the password or provide confirmation.
2. Locate and then click to select the following registry key:
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Rpcxdr\Parameters
3. Right-click DefaultConcurrentConnections, and then click Modify.
4. In the Value data box, type a value to increase the number of concurrent connections, and then click OK.
   
   Note The default value of the DefaultConcurrentConnections parameter is 256. You can increase this value up to a maximum of 8192.
5. Locate and then click to select the following registry key:
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Rpcxdr\Parameters
6. Right-click MaxConcurrentConnectionsPerIp, and then click Modify.
7. In the Value data box, type a value to increase the number of connections per IP address, and then click OK.
   
   Note The default value of the MaxConcurrentConnectionsPerIp parameter is 16. You can increase this value up to a maximum of 8192.
8. On the File menu, click Exit to exit Registry Editor.

Note By default, members of the Administrators group are not granted permission to change registry values in Windows Vista and later versions. To change the registry values, the user must take the ownership of the registry key in question. After the changes are made to the registry, we recommend that you change ownership back to the NT SERVICE\TrustedInstaller user.

A computer that is running Windows Server 2008 or Windows Server 2008 R2 can be used for VMware virtualization storage. Each virtual machine (VM) that is running on the VMware hypervisor requires two TCP connections to the NFS. By default, a computer that is running NFS on Windows Server 2008 or on Windows Server 2008 R2 supports 16 TCP connections per IP address. This allows only eight VMs to connect to the VMware virtualization storage on the NFS. For VMware virtualization storage authorization on a NFS server that is running Windows Server 2008 or Windows Server 2008 R2, the maximum number of NFS connections per IP address must be increased by using the steps that are mentioned in the "Resolution" section. With these steps, you can increase the number of NFS TCP connections up to a maximum of 8192.

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