The Virtualization Room

Nov 14 2007   12:23PM GMT

Return of the MAC

Kutz Profile: Akutz

Chris Wolf and I were presenting Virtualization 101 in Seattle yesterday when something he said sparked an idea in my usually dormant brain. Okay, it’s not usually dormant, but Seattle is so cold I think half of my synapses aren’t firing! In the process of discussing virtual machines (VMs), Chris mentioned that each major virtualization solutions provider has registeredĀ itself with the Institute of Electrical and Electronics Engineers (IEEE) and received one or more Organizationally Unique Identifiers (OUIs). An OUI is 24-bit number that makes up the first half of all of the Media Access Control (MAC) addresses assigned by an organization to devices it produces. MAC addresses are most frequently associated with Ethernet adapters, so why are virtualization vendors registering with the IEEE to obtain OUIs?

Virtualization vendors also produce Ethernet adapters — virtual network interface cards (NICs). Most VMs would be rather useless if they could not access some sort of network, so virtualization vendors must create virtual NICs in order for the VMs to get on the big wide world of Webs. And since these virtual NICs have to participate on the network just as if they were physical, they must use MAC addresses. Because the first 24 bits of these MAC addresses, the OUI, is organization-specific, there is a real potential for network administrators to detect not only if a machine on the network is virtual by its MAC address, but also what type of virtual machine it is (what vendor’s software is hosting it). While best practices dictate that you do not change the MAC address of VMs, enterprise virtualization solutions do present this as an option, and, because of this, here is the scenario I see occurring.

One way to harden the Apache Web server is to use mod_security to alter the Web server’s signature. For example, you can fool clients into thinking that the Web server hosting their favorite videos is actually a Microsoft Internet Information Systems (IIS) 5.0 server instead of Apache 2.2. Administrators do this in order to fool attackers into attempting the wrong types of attack vectors. Even though best management practices dictate that administrators NOT alter their VMs’ MAC addresses, I forsee them doing so anyway in order to fool would-be hackers into attempting the incorrect attack vectors on VMs. For example, if a VM is hosted on ESX and its MAC address has an OUI registered by Microsoft, then a would-be attacker may try known Microsoft Virtual Server or Hyper-V exploits on the VM instead of ESX exploits.

Who knows? Twelve months from now altering a VM’s MAC address to be that of another vendor may be considered a best practice, but right now, with the already complex problem of managing virtual hardware, IT administrators are best served to leave their VM MAC addresses well enough alone.

Of course, that doesn’t stop the idea from being completely and utterly cool!

Hope this helps!

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