cucsSwEthEstcEpRn is the Relative Name (RN) of a single established (currently pinned) LAN Ethernet uplink port on a Cisco UCS fabric interconnect (a cucsSwEthEstcEp row) -- the naming fragment that distinguishes it from its sibling instances under the same parent object. UCS Manager builds the full DN by appending this RN to the parent's DN, so it is the piece an admin or script uses to tell this pinned LAN uplink port apart from others attached to the same parent. For instance, comparing the RN values under one parent quickly tells an admin which specific sibling -- among several instances of the same class -- this pinned LAN uplink port refers to.