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Emerging IEEE Ethernet standards could soothe data center headaches

By , Network World
January 18, 2010 12:02 AM ET

Page 2 of 3

The bg and bh standards are expected to be ratified around mid-2011, according to those involved in the IEEE effort, but pre-standard products could emerge late this year. Specifically, bg addresses edge virtual bridging: an environment where a physical end station contains multiple virtual end stations participating in a bridged LAN. VEPA allows an external bridge -- or switch -- to perform inter-VM hairpin forwarding of frames, something standard 802.1Q bridges or switches are not designed to do.

"On a bridge, if the port it needs to send a frame on is the same it came in on, normally a switch will drop that packet," says Paul Congdon, CTO at HP ProCurve, vice chair of the IEEE 802.1 group and a VEPA author. "But VEPA enables a hairpin mode to allow the frame to be forwarded out the port it came in on. It allows it to turn around and go back."

VEPA does not modify the Ethernet frame format but only the forwarding behavior of switches, Congdon says. But VEPA by itself was limited in its capabilties. So HP combined its VEPA proposal with a Cisco's VN-Tag proposal for server/switch forwarding, management and administration to support the ability to run multiple virtual switches and multiple VEPAs simultaneously on the endpoint.

This required a channeling scheme for bg, which is based on the VN-Tag specification created by Cisco and VMware to have a policy follow a VM as it moves. This multichannel capability attaches a tag to the frame that identifies which VM the frame came in on.

But another extension was required to allow users to deploy remote switches -- instead of those adjacent to the server rack -- as the policy controlling switches for the virtual environment. This is where 802.1Qbh comes in: it allows edge virtual bridges to replicate frames over multiple virtual channels to a group of remote ports. This will enable users to cascade ports for flexible network design, and make more efficient use of bandwidth for multicast, broadcast and unicast frames.

The port extension capability of bh lets administrators choose the switch they want to delegate policies, ACLs, filters, QoS and other parameters to VMs. Port extenders will reside in the back of a blade rack or on individual blades and act as a line card of the controlling switch, says Joe Pelissier, technical lead at Cisco.

"It greatly reduces the number of things you have to manage and simplifies management because the controlling switch is doing all of the work," Pelissier says.

What's still missing from bg and bh is a discovery protocol for autoconfiguration, Pelissier says. Some in the 802.1 group are leaning towards using the existing Logical Link Discovery Protocol (LLDP), while others, including Cisco and HP, are inclined to define a new protocol for the task.

"LLDP is limited in amount of data it can carry and how quickly it can carry that data," Pelissier says. "We need something that carries data in the range of 10s to 100s of kilobytes and be able to send the data faster rather than one 1,500 byte frame a second. LLDP doesn't have fragmentation capability either. We want to have the capability to split the data among multiple frames."

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