Virtualization - Mixing DMZ and internal guests on one host: would you?

[Dan Lynch <DLynch () placer ca gov>]

Greetings list,

I'm providing security input for a proposed redesign and upgrade of our existing VMWare implementation. We have 80 some 
odd internal-use-only production servers like Windows AD domain controllers, file servers, and MS Exchange servers on 
one existing ESX 3.x cluster. A separate ESX 3.x cluster hosts exclusively DMZ-based public web servers. A single 
virtual center server manages both clusters.

As existing hardware leases expire, a new cluster is proposed to be built on new hardware that would merge all our VMs 
on one vSphere cluster. Dedicated pSwitch and pNIC hardware, and separate vSwitch instances are proposed to separate 
high risk from high value systems. This still leaves open the possibility of accidental (or intentional) 
misconfigurations crossing security boundaries, and the lower risk of guest-to-host or guest-to-guest exploit. 

Haletky warns against just this design in his "VMware vSphere and Virtual Infrastructure Security" book, but the cost 
of an additional cluster may override. What is the community take on this? Would you do it? Do you do it? If so, what 
controls have you put in place to help mitigate the risk?

Thanks for any input.




Dan Lynch, CISSP
Information Technology Analyst
County of Placer
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