UCS Fabric Interconnects are deployed in a cluster configuration from the control plane perspective. A Fabric Interconnect pair is in active/standby configuration. The active Fabric Interconnect is called primary and the standby Fabric Interconnect is called subordinate.
All control plane communication is handled by the primary Fabric Interconnect that manages the main configuration database. The main configuration database is stored on the primary and replicated on the subordinate Fabric Interconnect. The primary sends updates to the subordinate when configuration changes occur through dedicated Ethernet links called L1/L2.
In a situation where the Fabric Interconnect running the primary instance fails, the subordinate Fabric Interconnect takes the role of primary instantaneously. Access to UCS Manager stops, and you need to log out and log back in. In a split brain...
