Amid the excitement of virtualizing server, storage and desktop resources, the network hasn't received much attention. As these virtual resources take their places in the New Data Center, however, the network will emerge from behind the scenes to command center stage and play a pivotal role in tomorrow's virtualized environments.

This isn't to say the concept of network virtualization is new - virtual LANs (VLAN), VPNs and MPLS, enabling multiple virtual connections to share bandwidth resources on one network pipe, are longtime favorites. The rush to virtualize multiple infrastructure and application resources, however, is changing the rules for network virtualization, and IT managers are gearing up for the network's second act. (Compare storage virtualization products.)

"Virtualization is the most disruptive technology to hit networking in 10 years. It's the first computing architecture that has a high network dependency, which means the network architecture going forward has to be in lock step with server, storage and desktop," says Robert Whiteley, an analyst at Forrester Research. "The network historically has been plumbing that everything rode on top of. Now it is becoming the new backplane," he says.

Jeremy Gill, CIO of Michael Baker Corp., a civil engineering firm in the Pittsburgh area, agrees. "When we think of virtualization in a large environment, the more we can push down to the network layer, the better we will be from a total-cost-of-administration standpoint," he says. "VMware took a great first step with x86 server virtualization, but now it's time to embed this knowledge at the network layer."

Flat-as-a-pancake networks

For the network to serve a virtual environment best, however, some cardinal rules of networking must change, industry watchers say. For one, the flexibility and portability of virtual-server resources demand that the traditional, three-tiered network architecture - edge, distribution and core switches - collapse into a flat landscape across which virtual machines can be allocated and reallocated.

"Server virtualization has very much blurred the line of where the network stops and the server begins," says Andreas Antonopoulos, an analyst with Nemertes Research.

Take VLANs in a virtual-server environment, for instance. Administrators might use a Layer 2 VLAN to allow virtual machines to travel freely between two data centers while remaining on the same subnet. Because Layer 2 routing is local and Layer 3 is used to go from one subnet to another, this type of design "goes against everything taught in traditional networking," Antonopoulos says. "It violates the sacred cows of networking and makes no sense using the old rules."