"Reinitialize the MAC address of all network cards"?

[cgwaters]

I'm attempting to clone a VM (Windows 7) using the VirtualBox GUI. The first page of the cloning wizard contains an option to "Reinitialize the MAC address of all network cards". The default is to NOT perform this action. What are the repercussions of cloning a VM with--and without--this option being selected? The Help feature doesn't seem to mention it and I couldn't find any references on the forums nor Internet-wide via Google.

[BillG]

It is necessary if you plan to run the cloned vm on the same network as the original. Two machines on the same network cannot have the same MAC address. If the clone will never see the original on the network it is not required. I would not expect to find much discussion online yet since this option only beame available with the latest release (4.1.0) recently.

[bogstad]

The result of not reinitializing the MAC addresses is that both VMs will have virtual Ethernet cards with the same Ethernet (MAC) address. If both VMs are ever run at the same time while connected to the same Ethernet, then they and the other machines (real or virtual) connected to the same Ethernet will get very confused. The only network mode which probably won't have a problem is NAT. Under the wrong setup; Bridged, Internal, and Host-only will definitely have problems. Even if you only run one VM at a time, it would be like calling your home phone number and if no one was home at your house it would ring at your neighbor if they were home. Maybe that's okay or maybe not. On the other hand, if you have software licenses that use your Ethernet cards address to enforce licensing restrictions then you might want to use the same MAC if your were cloning the system before doing updates which you might want to rollback. (I would probably do a snapshot instead myself.) Hopefully, this gives you some idea of the issues you should consider. The right decision is going to be dependent on exactly what you plan to do with the original as well as cloned VM as well as your operating system. Unfortunately, I believe that the network card figures prominently on when Microsoft OSes decide if you need to reactivate your license. If you leave everything else the same besides the network card you might get away with it. Start changing other things and expect to need to reactivate.

[cgwaters]

Thanks for the replies. So if the cloned VM will be active on the same network at the same time, the MAC address should be configured to be reinitialized; but that could cause licensing issues, at least with Windows.

I have an MSDN license--which provides a handful of unique product keys, so I don't have to worry too much about licensing issues It is my intention to run, at the same time, the original VM and one or two cloned VMs. So I should have reinitialized the MAC address. Is there a way to do that to the cloned VM *after* it has been created?

[Perryg]

Is there a way to do that to the cloned VM *after* it has been created?

Yes there is. Go to the settings for the new guest (while shutdown) and the network section. Open the advanced section and you will see the MAC address. Click the dbl arrow to the right to generate a new MAC address.

[cgwaters]

Great! Thanks for the information, everyone.

[Ahmed]

If both VMs are ever run at the same time while connected to the same Ethernet, then they and the other machines (real or virtual) connected to the same Ethernet will get very confused. The only network mode which probably won't have a problem is NAT. .

Hello. Not sure if you are still responding to this message thread, but can you please elaborate why you feel there "might" not be a problem if the port is attached to a NAT.

Thank you,
A.

[Rootman]

Unfortunately, I believe that the network card figures prominently on when Microsoft OSes decide if you need to reactivate your license.

I do not believe this is the case as MANY users have changed NICs without having to reactivate, at least in the past when a NIC was a separate card. If this is the only thing that has changed I think Windows will ignore it. I think the CPU ID is mainly what really counts.

The MAC plays a part in the DHCP request for an IP, if it has the SAME MAC the DHCP server cannot tell it is a different machine and will assign the same IP address to it and create an IP conflict.

[mpack]

In XP the MAC address had a high weighting, however it still needed something else to change. It's possible the MAC was downgraded since then, I've had no reason to investigate.