Despite competing standards and proprietary alternatives already on the market, the IETF insists that TRILL is gaining momentum as a method for solving Ethernet scalability problems in data center networks.
Indeed, the industry appears deeply fractured over the best approach, with some vendors backing the IETF's TRILL, some backing the IEEE's SPB, others offering proprietary protocols and still others advocating a combination of approaches.
TRILL was designed as a way to overcome limitations of Ethernet's Spanning Tree Protocol, a method for preventing network loops and for handling backup paths in the event of a failure. Spanning Tree is inefficient because it doesn't use all of the available paths between switches, and the routes are not always the shortest or fastest. Because of this, topology reconvergence in a Spanning Tree network is slow, which limits scale and make the network more susceptible to link failures.
The IETF is attempting to address this deficiency in RFC 5556 with TRILL, which stands for Transparent Interconnection of Lots of Links. TRILL is a Layer 2 protocol that uses link state routing to map the network, discovering and calculating shortest paths between TRILL nodes called Routing Bridges, or RBridges. This enables shortest-path multihop routing so users can build large-scale Ethernet and Fibre-Channel-over-Ethernet data center networks.
Ethernet switch market leader Cisco is shipping FabricPath for its Nexus 7000 switch, a technology that accomplishes the same tasks TRILL is intended to address while providing many more capabilities. Cisco says FabricPath is a "superset" of the TRILL standard.
Brocade also says its BrocadeOne fabric architecture is based on TRILL.
Juniper, though, just announced its QFabric line of data center and cloud fabric switches, which do not support TRILL at all but instead support a proprietary method for scaling Ethernet in data centers.
Indeed, Juniper is an outspoken TRILL detractor. At its QFabric announcement, Juniper Founder and CTO Pradeep Sindhu called TRILL "a solution looking for a problem" and "a means to scale Layer 2 networks, but most [data center] networks want to communicate at Layer 3. Layer 3 gets punted to a one-armed router and becomes a choke point," Sindhu said. "TRILL as applied to a data center is a joke."
HP is supporting both TRILL and a competing IEEE specification called Shortest Path Bridging (SPB). SPB is an extension to the Multiple Spanning Tree Protocol that also uses a link state routing protocol to allow switches to learn the shortest paths through an Ethernet fabric and dynamically adjust to topology changes.
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