The IETF has standardized Transparent Interconnection of Lots of Links (TRILL)@ a protocol for least-cost transparent frame routing in multi-hop networks with arbitrary topologies and link technologies@ using link-state routing and a hop count. The TRILL base protocol standard supports the labeling of TRILL Data packets with up to 4K IDs. However@ there are applications that require a larger number of labels providing configurable isolation of data. This document updates RFC 6325 by specifying optional extensions to the TRILL base protocol to safely accomplish this. These extensions@ called finegrained labeling@ are primarily intended for use in large data centers@ that is@ those with more than 4K users requiring configurable data isolation from each other.