Virtualization Vs. Networking

Server virtualization has been a boon for IT, but it creates challenges for the network. Virtualization reduces the number of physical servers, but it snowballs the number of virtual and network devices. That causes networking issues because, from a switching perspective, there's little difference between a virtual network port and a physical one.

This paradox of server simplicity vs. network complexity is analogous to what would happen if thousands of commuters gave up their individual cars for shared minivans, with each passenger going to a different destination. While this would reduce the number of vehicles on the freeway, it doesn't reduce the number of trips--the driver still must crisscross town dropping off passengers at their offices.

Ride sharing also complicates the routing calculus. Instead of each commuter finding the quickest path between home and office, the van driver must optimize the pickup and delivery schedule to minimize drive time and distance.

Likewise, many of the switching problems that come up with virtualization have to do with performance and management complexity.

For example, aside from merely increasing the number of network devices, virtualization adds tiers to the switching fabric, increasing latency, power consumption, and complexity. The consolidation of virtual machines on physical servers also affects switching scalability and performance. A hypervisor virtual switch with a workload of 10 to 15 VMs per system extracts a modest overhead of about 10% to 15%, but that figure that will undoubtedly increase when handling scores of VMs.

Other problems include management and security complications. As more traffic is switched within the hypervisor, traditional network monitoring and security tools lose visibility into a significant amount of network activity.

Problem Solvers

Two new IEEE standards projects aim to help with these and other problems. Both are amendments to the base IEEE 802.1Q VLAN tagging standard.

The more mature project is 802.1Qbg Edge Virtual Bridging. It's designed to let multiple VMs share a common port while obtaining services from an external bridge (that is, an edge switch acting as a reflective relay). Normally, Ethernet frames aren't forwarded back out of the same interface they came in on. This action, called hairpinning, causes a loop in the network at the port. EVB provides a standard way to solve hairpinning. It's a simple protocol extension that can be implemented on existing hardware with a software upgrade to the switch and hypervisor.

Meanwhile, the 802.1Qbh Bridge Port Extension project tackles policy management. The Qbh port extension standard adds a tag, much like standard VLAN tags, allowing network flows to be mapped to specific VMs and followed as those VMs move about the network.

New technology and standards are emerging to address many of the issues raised by virtualization's impact on the network, but companies must ensure that virtualization's benefits in one sector don't turn into problems in another.

While the journey toward a highly virtualized infrastructure will be long, and at times arduous, the result will bring the enterprise to new levels of performance, reliability, agility, and efficiency.

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