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I'm looking to build a series of VMWare Virtual Machines as my client needs them.

The hostnames and IPs have been pre-assigned. But I'm going to need to add rules to our switches for each host's MAC address.

I'm trying to find out if I can predict the MAC addresses that are going to be generated.

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Out of curiosity, why add rules to the switches? Security policy or something else? – Jed Daniels Nov 22 '10 at 23:02
Yeah, only known mac addresses inside specific networks can communicate outside of that network. – St. John Johnson Nov 22 '10 at 23:26
I have no knowledge of how VMWare generates MAC addresses but I do know that security by MAC address is an absolute nightmare and massively prone to error. I can't think of a single circumstance when this would be preferable to using ACLs on the router. – blankabout Apr 22 '11 at 6:34
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3 Answers

up vote 4 down vote accepted

You can hard code them in a VM, but you can't predict them if you allow vmware to auto-generate them. VMware has a lot of different KB articles that mention this topic, but I think this one is the best place to start.

Some things to keep in mind:

  1. If you statically assign them, you must use the allowed range that VMware defines.

  2. If you replicate/copy/duplicate a VM that has a static assignment, you will have problems if it is on the same broadcast domain.

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As I'm sure @Jed knows, that should be broadcast domain, not collision domain. – blankabout Apr 22 '11 at 4:48
@blankabout Thanks! Yea, I do know better, but I wasn't really paying attention. So noted, and corrected. +1 on the comment. – Jed Daniels Apr 22 '11 at 6:08
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up vote 2 down vote

You can set a static MAC by following the instructions in this link. That should give you all the control you're looking for.

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Another thing to keep in mind is that the static MACs can be fragile. I can't remember the exact situations, but upgrading the guest's tools, changing the vNIC type, or doing a VMWare Convert could trigger the MAC address to change.

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