PortLand tries to solve extremely similar problems as VL2: making the network appear flat and allowing VMs to migrate gracefully, reducing amount of configuration necessary, efficient communication between any pair of nodes. Again, this is definitely a real issue.
PortLand uses a "PMAC" (pseudo-MAC) address to abstract away physical location details; this is similar to the directory lookups used in VL2. It seems that these two systems are taking very similar approaches; add another layer of abstraction to make physical location transparent to the application developer. PortLand seems to place less emphasis on providing high bandwidth between any pair of servers, instead not requiring a change in network topology and focusing on fault tolerance (whereas VL2 adds a more dense linking structure to provide high bandwidth).
Since both of these papers are 7 years old, I am curious to know if either of these systems (or something similar) is in use anywhere. I'm sure some of the ideas have appeared by now, and it would be interesting to find which approach was more successful. It is my intuition that PortLand's approach with fewer network links required probably appears more often, though I don't think I have ever heard of any PMAC approach to a physical-layer-hiding abstraction.
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