VMware Workstation vmnat.exe high CPU load

Thu-2011-10-06 5 Comments

Vmnat.exe provides NAT services to virtual machines running in VMware Workstation. I don’t know why, but I have experienced high CPU loads of this process on Windows 7 Professional and Ultimate x64 SP0 and SP1 versions with VMware Workstation 7 and 8. I finally know how to fix it.

If you experience high CPU load from the vmnat.exe process, do the following:

Close all VM’s and VMware Workstation. Start the Virtual Network Editor from your start menu.

 

 

Now press the Restore Default button. VMware will reset all virtual interfaces.

I ended up with a Host-only network type VMNet1 and a NAT network type VMNet8. I reckon this will be the same for you.

Don’t forget to check the VM’s that need to use a NAT network connection.

Filed under VMware, Windows

About Yuri de Jager
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5 Responses to VMware Workstation vmnat.exe high CPU load

  1. Simon Haslam says:
    Tue-2012-05-08 at 8:03 PM

    Thanks for the post Yuri – I’ve been having a similar/same problem: runs fine for a while then vmnat ramps up to taking a steady 25% cpu (core i7 mobile, Win7 SP1 64 bit). You mention “Don’t forget to check the VM’s that need to use a NAT network connection” – what do we do about them if we want them to use NAT (e.g. so that they can have stable internal addresses and just port forward one or two key ports)?

    Reply
    • Yuri de Jager says:
      Wed-2012-05-09 at 10:27 AM

      Hi Simon,

      It’s been a while since I posted this, but this ‘fix’ is only for the high CPU load. It doesn’t change any functionality. You can still use the NAT network in your VM after the reset.

      You can see that the reset changed the subnet of the NAT network. That’s why I mentioned that you should check your VM’s.

      I hope this explanation helpes you somewhat.

      Cheers,
      Yuri

      Reply
      • Simon Haslam says:
        Mon-2012-05-14 at 12:33 PM

        Ah, OK – I hadn’t read carefully enough – so NAT on VMnet8 is going back to the default, including the default subnet. In my case I have changed the subnet and wouldn’t really want to change my (Oracle) VM IP addresses.

        I’ve found if I kill vmnat.exe from Windows the high CPU stops of course but the process does get restarted at some point – perhaps next time you start a VM using that interface – and works normally again.

        It is curious though… I wonder what the root cause is?

  2. xy says:
    Wed-2012-06-13 at 1:55 AM

    I have still the problem after restoring the default settings. After a while working with a VM in the VMware Player the CPU load of the vmnat.exe starts again to be aroun 40-50 percentage… Is there a workaround which really solve it or is this a known bug?

    Reply

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