The virtual NIC type remains as flexible even after installing VMware Tools or upgrading Virtual Hardware version (2108662)

Purpose

To provide an explanation to why a virtual NIC of a virtual machine remains as flexible even after installing VMware Tools or upgrading the Virtual Hardware version.

Resolution

Modern Guest Operating Systems such as Windows 2008 does not support this type of adapter and does not provide an option to select flexible when creating a virtual machine. Although legacy Operating System such as Windows 2003 still provides this option, this type of virtual NIC should only be used as a placeholder until you decide which vNIC will need to be configured for the virtual machine.

For more information, see Choosing a network adapter for your virtual machine (1001805).

Converting from flexible to VMXNET is an automated process during a VMware Tools installation following a reboot of the virtual machine.

To confirm that the virtual NIC has changed from flexible to another type:

1. Log in to the Windows Guest OS with no VMware Tools installed.
2. Open a command prompt and run command to display the adapter configuration.
   
   ipconfig /all
   
   Note: Notice the Adapter type is AMD PCNET Family PCI Ethernet adapter.
   
3. Install VMware tools.
4. Once installation completes, reboot the virtual machine.
5. Log back in to the Windows Guest OS and re-open the command prompt.
6. Re-run command:
   
   ipconfig /all
   
   Note: Notice the Adapter type is now VMware Accelerated AMD PCnet adapter.

If you choose to use VMXNET2 or VMXNET3, delete the existing virtual NIC of the virtual machine. Then add a new virtual NIC and configure with the desired type such as VMXNET2 or VMXNET3.

Source KB:-

http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2108662#sf36549405&src=vmw_so_vex_ragga_1012