A Clos network architecture is the answer to the network problems of modern data center, suggests Dinesh Dutt, distinguished engineer at Cisco. A Clos network is a three-stage architecture that dates back to the early 1950s telephone switching systems.

Following Ethernet’s victory over InfiniBand and Fiber Channel in data center networks, the problem arose of making Ethernet work in today’s highly virtualized data centers, where traffic increasingly travels horizontally as opposed to vertically.

Cisco’s competitor, Juniper, announced its architecture solution to the problem on 23 February: QFabric. Dutt’s proposed solution is Clos, more particularly Clos implemented using the TRILL (Transparent Interconnect of Lots of Links) standard.

Dutt is a co-author of the standard, currently being developed by the Internet Engineering Task Force. Using TRILL is one of several ways to build a CLOS network.

Dutt said during a presentation at the Ethernet Technology Summit in Santa Clara, California, on the day following Juniper’s announcement, that to meet requirements of modern data center networks, data center managers “should build a network which is a fat tree – a Clos.”

He also said Cisco’s recently announced FabricPath technology was a good way to implement a Clos network. The two-layer architecture, according to him, addresses all requirements of modern data center networks: fine-grained failure domains, scalability, open systems, lower CapEx and OpEx and simpler management.

The architecture offers fine-grained failure domains because every switch in the access layer is connected to every switch in the aggregation layer. A failure in one switch in either of the layers does not bring down the entire network.

Clos affords scalability and TRILL addresses VM mobility “quite effectively”, he said. Because it is an open standard, TRILL also helps prevent vendor lock-in.

This last issue has not been addressed by Juniper’s QFabric, whose three key components are Juniper products, controlled by the company’s Junos operating system.

Alex Gray, senior VP and general manager at Juniper’s Ethernet Switching Business Unit, however, said the company was open to standardizing QFabric on one of the protocols if the market shows demand for that. Gray delivered a presentation about QFabric at the summit before Dutt.

Key to simplifying management of large-scale data center networks, Dutt said, was providing standard APIs for customers that allow them to build their own tools.