Glad to see this has been posted and we can talk about it now... please share your experiences and let us know if these tips work for you and what sort of performance benefits you've noticed when using this new driver.
We've been switching our Windows and Linux VMs to use "VMXNET Enhanced" for some time now and see public information on the new VMXNET3 NIC for guests...
This Thread has been started to help with procedures on the conversion of existing machines from older NIC to newer NIC as it is not 100% straightforward and there are some tricks to remove old hardware and change to new hardware. This would be similar in the physical world to changing from a 100 BaseT PCI Card to a GigE card. The old drivers need to be removed, new drivers installed, and IP Addresses moved over. If you just remove the old NIC and install the new one you may end up with a IP Address Conflict error saying the Address you are trying to use is already in use on another Network Interface. The problem is that when you open Device Manager the old NIC is hidden. See below for steps on how to overcome this.
Question: What is VMXNET3?
Answer: VMXNET3 builds upon VMXNET and Enhanced VMXNET as the third generation paravirtualized virtual networking NIC for guest operating systems.
New VMXNET3 features over previous version of Enhanced VMXNET include:
• MSI/MSI-X support (subject to guest operating system kernel support)
• Receive Side Scaling (supported in Windows 2008 when explicitly enabled through the device's Advanced configuration tab)
• IPv6 checksum and TCP Segmentation Offloading (TSO) over IPv6
• VLAN off-loading
• Large TX/RX ring sizes (configured from within the virtual machine)
What's New in vSphere 4.0
VMware vNetwork module that encompasses the vDS and VMXNET-3 enables inline monitoring and centralized firewall services and maintains the virtualmachine's network run-time characteristics.
Flexible shows up in Windows Device Manager as an “VMware
Accelerated AMD PCNet Adapter” and Enhanced vmxnet show up as “VMware
PCI Ethernet Adapter”.
Flexible — The Flexible network adapter
identifies itself as a Vlance adapter when a virtual machine boots, but
initializes itself and functions as either a Vlance or a vmxnet
adapter, depending which driver initializes it. VMware Tools versions
recent enough to know about the Flexible network adapter include the
vmxnet driver but identify it as an updated Vlance driver, so the guest
operating system uses that driver. When using the Flexible network
adapter, you can have vmxnet performance when sufficiently recent
VMware tools are installed. When an older version of VMware Tools is
installed, the Flexible adapter uses the Vlance adapter (with Vlance
performance) rather than giving no network capability at all when it
can’t find the vmxnet adapter.
Enhanced vmxnet — The enhanced vmxnet adapter is
based on the vmxnet adapter but provides some high-performance features
commonly used on modern networks, such as jumbo frames. This virtual
network adapter is the current state-of-the-art device in virtual
network adapter performance, but it is available only for some guest
operating systems on ESX Server 3.5. This network adapter will become
available for additional guest operating systems in the future.
Networking Error, IP Address Already Assigned to Another Adapter
KB Article 1179
Updated Jan. 07, 2009
Why do I see an error message that “The IP address XXX.XXX.XXX.XXX…” is already assigned to another adapter?
Under certain conditions, you may see the following error message from a Windows guest operating system:
The IP address XXX.XXX.XXX.XXX you have entered for this network
adapter is already assigned to another adapter Name of adapter. Name of
adapter is hidden from the network and Dial-up Connections folder
because it is not physically in the computer or is a legacy adapter
that is not working. If the same address is assigned to both adapters
and they become active, only one of them will use this address. This
may result in incorrect system configuration. Do you want to enter a
different IP address for this adapter in the list of IP addresses in
the advanced dialog box?
In this message, XXX.XXX.XXX.XXX is an IP address that you are
trying to set and Name of adapter is the name of a network adapter that
is present in the registry but hidden in Device Manager.
This can occur when you change a network connection’s TCP/IP configuration from DHCP to a static IP address if:
You have upgraded VMware virtual network adapters (for example
when you migrate a virtual machine from an older to a new version of
You have added and removed network adapters multiple times.
The cause of the error is that a network adapter with the same IP
address is in the Windows registry but is hidden in the Device Manager
(My Computer > Properties > Hardware > Device Manager). This
hidden adapter is called a ghosted network adapter.
Using the Show hidden devices option in the Device Manager (View
Show hidden devices) does not always show the old virtual NIC
(ghosted adapter) to which that IP Address is assigned
Microsoft addresses this issue in their Knowledge Base article
269155, which is available at the time of this writing at
To resolve this problem, follow these steps to make the ghosted
network adapter visible in the Device Manager and uninstall the ghosted
network adapter from the registry:
1. Select Start > Run.
2. Enter cmd.exe and press Enter.
3. At the command prompt, run this command:
4. Enter Start DEVMGMT.MSC and press Enter to start Device Manager.
5. Select View > Show Hidden Devices.
6. Expand the Network Adapters tree (select the plus sign next to the Network adapters entry).
7. Right-click the dimmed network adapter, and then select Uninstall.
8. Close Device Manager.