Which device connects Cisco UCS B-Series servers to Cisco Fabric Switches?

A Fabric Extender (FEX) connects the blade servers within a UCS chassis to the Fabric Interconnects, but it does not directly connect to external Cisco Fabric Switches.

A host bus adapter (HBA) is a component within a server that provides connectivity to storage devices, not a device that connects servers to external fabric switches.

Cisco Fabric Interconnects serve as the primary switching components in a UCS domain, providing unified connectivity for LAN and SAN traffic from the B-Series blade servers to external network and storage devices, including Cisco Fabric Switches.

A fabric switch is a general term for a switch in a fabric network; however, in the context of connecting UCS B-Series servers to the broader network, the specific and correct device is the Fabric Interconnect.