14 Responses

  1. Michael Webster
    Michael Webster at |

    MAC address changes and forged transmits are also used by Windows as a mechanism to protect against duplicate IP addresses on the network. If a Windows system detects an IP address conflict it will send out a forged transmit to reset the IP to the original MAC of the machine it think originally owned it and then take itself off the network. This protection mechanism for duplicate IP addresses won’t work without these security settings allowed.

    1. Michael
      Michael at |

      @Michael — can you comment on which versions of windows send out a forged transmit as part of dealing with IP address conflicts? So far I am only able to reproduce this with Windows 2003. Windows 2008 R2 does not appear to exhibit the same behavior.

  2. chwilówki dla firm
    chwilówki dla firm at |

    I was wondering if you ever considered changing the structure of your
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  3. Rejecting VMware MAC Address Changes Explained via @ChrisWahl | Wahl Network

    […] Additionally, there seems to be confusion between MAC Address Changes and Forged Transmissions: you can read about those here! […]

  4. Blog Series: ESXi 5 STIG – ESXi Server Everything Else | VM Field Tips

    […] How The VMware Forged Transmits Security Policy Works Rejecting VMware MAC Address Changes Explained […]

  5. vikrant pawar
    vikrant pawar at |

    This is fair, however have you tried same stuff with DSwitch and VLan we did and it’s not working as expected,

    We want ESXi to add vLan tag for packets from Nested VM but it’s not adding any tag for them.

  6. Configuración de políticas de seguridad de vSwitch con PowerCLI |

    […] cada parámetro. Chris Wahl tiene un par de posts excelentes donde explica MAC Address Changes y Forged Transmits. En cuanto a Promiscuous Mode, cuando se habilita, permite a las VMs que se encuentran en el […]

  7. kaveh
    kaveh at |

    Is there any point in having Forged transmits set to allowed if and when Mac address changes are set to reject? If I understand correctly the latter setting drops the connection completely so setting Forged transmitts to allowed would not take to effect! correct?

  8. Virtual Switch Deep Dive - Part I - Virtualoco
  9. How to set up the UNetLab or EVE-NG network emulator on a Linux system | Open-Source Routing and Network Simulation

    […] that nested virtual machines running inside a VMware virtual machine can communicate with external networks, change the […]

  10. Steve Hummel
    Steve Hummel at |

    We used manual MAC addresses for License servers that have licenses tied to the MAC address. I do this through the windows nic config and have only ever accepted the MAC Change and not the Forged Transmit. This week, I had both of my license servers lose network access after a reboot. I finally tracked it down to the Accept Forged Transmit setting and once I accepted them, the machines were back on the net again. This behavior was for win2k3, win7, and win2k12r2 VMs. I’m not sure what changed in the environment that caused this behavior to suddenly change. It had to be either a window patch or vmtools update.

  11. Ral Navalgund_Bangalore
    Ral Navalgund_Bangalore at |

    Hi All,

    I tried to accumulate all articles by Chris, However i found all in one book . Ii is handy all VM NW concepts explained clearly..

    “Networking for VMware Administrators (VMware Press Technology) 1st , Kindle Edition
    by Christopher Wahl (Author),‎ Steve Pantol (Author) ”

    Thanks Chrish.

    Raj Navalgund_ Banglaore

  12. David Paulus
    David Paulus at |

    Hi all,

    I have a question about the settings. Until now we use the default settings = Accept, but we want to change it to Reject but the problem is I know for some VM’s this will be a problem but I don’t know which VM. Is there a way to see with some reporting tools or commands which VM will have problems with Rejecting forged transmit and MAC Address change.

    David Paulus


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