I didn’t know this but apparently HyperV has an algorithm to generate new MAC address per host, but it doesn’t check to see if this MAC address is unique to two HyperVs on the same subnet!

Robert Larson on virtualizationadmin.com has an interesting article which describes how MAC address pools work in Hyper-V, how it is possible to accidentally deploy hosts with duplicate MAC address pools, how to modify the default pool, how to detect if you are experiencing a duplicate MAC address situation with virtual machines, and how using SCVMM 2008 to manage your Hyper-V hosts can prevent duplicate MAC addresses.

http://www.virtualizationadmin.com/articles-tutorials/microsoft-hyper-v-articles/networking/mac-address-pool-duplication-hyper-v.html

Of course one solution is use a product that doesn’t do this. Hee-hee…

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