This CucsFabricFcSanUplinkTrunking field reports whether FC trunking (carrying multiple VSANs over a single physical uplink) is enabled for this FC SAN cloud. For the fabric interconnect's switched Fibre Channel/FCoE uplink domain, i.e. the SAN traffic reaches once it leaves the fabric interconnect toward an upstream FC/FCoE switch, enabling trunking here is what lets one physical FC uplink carry several VSANs' worth of SAN traffic at once instead of needing one dedicated physical uplink per VSAN, which directly affects how many uplink ports an admin needs to provision. If this reads 'disabled' while the design calls for multiple VSANs to share this uplink, that mismatch by itself explains why only one VSAN's traffic is actually getting through.