TRILL - Transparent Interconnect of Lots of Links
TRILL is short for Transparent Interconnect of Lots of Links.
The Transparent Interconnection of Lots of Links (TRILL) is an IETF specification that enables multipathing in the data center. The TRILL protocol provides transparent Layer 2 forwarding using encapsulation with a hop count and IS-IS link state routing.
Recommended Reading: Understanding The Data Link Layer.
The TRILL network protocol was first developed by Radia Perlman (also credited with the invention of the algorithm behind the Spanning Tree Protocol) to "remove deficiencies of bridged Ethernet networks in large Layer 2 campuses" and was then taken up by the IETF to create a new standard.
As defined by the IETF RFC 6326 standard, TRILL provides optimal pair-wise forwarding without configuration, safe forwarding even during periods of temporary loops, and support for multipathing of both unicast and multicast traffic as well as supporting VLANs.
TRILL introduces a new encapsulation layer, a set of associated control plane protocols, and a new network device type called an RBridge (a TRILL device) that sits midway between a router and a bridge.