IEEE 802.1Qbg/h to Simplify Data Center Virtual LAN Management
by George Lawton
Widespread virtualization has made data center operations more efficient, but it has also raised serious management issues. Each of the major virtualization platforms currently supports a unique virtual LAN protocol. Organizations with large data centers must therefore manage multiple virtual networking protocols.
In response, companies that normally compete for control of the data center market are working to develop standards for virtual Ethernet port aggregation (VEPA) to ease the management issues. The IEEE 802.1Qbg and 802.1Qbh VEPA standards will move networking from virtual servers to dedicated Ethernet switches. This will help centralize networking in dedicated equipments for better performance, security and management. It will also help reduce the computing overhead on virtual servers as they scale to support more virtual machines.
Traditional virtual switches generate several challenges, said Shehzad Merchant, senior director of strategy for Extreme Networks. The first is scaling. As data centers and IT managers add more virtual machines to physical servers, less horsepower is available for network processing tasks. Also, it's more difficult to troubleshoot problems using traditional network management tools because the traffic is switched on the server rather than through a dedicated switch.
Another issue is that the Xen Server, Hyper-V, and ESX virtual machine monitors, also known as hypervisors, each support a different virtual switch protocol so the network administrator has to deal with a heterogeneous network.
The new proposals have broad industry support. VEPA technology will be implemented by network equipment vendors, Ethernet card vendors, and hypervisor vendors. Companies working on the VEPA standardization include 3Com, Blade Network Technologies, Brocade, Cisco, Dell, Extreme Networks, HP, IBM, Intel, Juniper Networks and Qlogic.
The Qbg and Qbh proposals reflect two different approaches for implementing VEPA. The proposal championed by HP is being rolled into 802.1Qbg, which will be optimized for edge switches. Another approach, championed by Cisco, is being rolled into 802.1Qbh and optimized for centralized switches.
The lack of standardization isn't hampering the adoption of virtualization now, but Jon Oltsik, senior principal analyst at Enterprise Strategy Group, said that achieving virtualization's full benefits will require better integration between the physical and virtual worlds. "The way people are networking now using virtual switches in the hypervisor will not scale," he said. "It's holding back the industry."
Under the Hood
Virtualization technology enables multiple virtual servers to run on a hypervisor installed on one physical server. This helps improve computer utilization and application reliability, so the use of virtualization is exploding, particularly in data centers. Gartner predicts that 50 percent of all workloads will run inside virtual machines by 2012.
The hypervisor emulates all the hardware and network connections of a physical computer to each virtual machine. VEPA will let administrators move the virtual networking functionality from the hypervisor to a dedicated physical switch.
This hasn't been possible in the past owing to traditional Ethernet limitations that precluded "hairpin turns," in which data packets travel back through the same physical port they came from. Consequently, network traffic between virtual machines on the same physical server had to travel on a specialized virtual networking protocol running on the server. The new VEPA protocols allow these hairpin turns, so organizations can move network traffic between virtual machines off the server and on to dedicated network switches.
VEPA Challenges
One downside of VEPA is increased network traffic, since each data packet has to make a round-trip down the Ethernet cable rather than just going across the physical server's internal bus. Oltsik said that CPU performance is typically a more significant limiting factor on servers than network bandwidth. Today's networks generally support 10 Gbps and are expected to support 40 to 100 Gbps within the next two years. The processing overhead is a much bigger limitation.
One challenge to VEPA adoption is the legacy hardware that doesn't support hairpin-turn networking, said Merchant. Organizations will have to physically replace these switches and networking cards to adopt VEPA. However, vendors such as Extreme Networks are now shipping equipment that will be upgradable to VEPA with a software update.
Another challenge is infighting among the vendors between the two proposed standards. "The sooner they can agree on them, the sooner they can start putting VEPA into products," Oltsik said. "Having both Qbh and Qbg is an issue. But regardless of whether one gets adopted or both do, standardization is the right thing to do."
For more information about 802.1Qbg, see www.ieee802.org/1/pages/802.1bg.html; for more information about 802.1Qbh, see www.ieee802.org/1/pages/802.1bh.html.
George Lawton is a freelance technology writer based in Guerneville, California. Contact him at glawton@glawton.com.
