This paper proposes a third generation approach: multiple layers of tags to achieve isolation and designate routes through the data center network. The tagging protocol can be either carrier Ethernet or MPLS, both of which support multiple layers of tags.
Zeppelin - A Third Generation Data Center Network
Just like computation and storage, networks in data centers require virtualization in order to provide isolation between multiple co-existing tenants. Existing data center network virtualization approaches suffer drawbacks. None of the approaches meshes easily with existing provider wide area VPN technology, which uses MPLS.