Which of the following identifiers occur in a storage fabric once and is always unique?

A Node Symbolic Link Name is a user-defined, human-readable name and is not inherently globally unique or assigned by the hardware manufacturer.

The World Wide Port Name (WWPN) is a globally unique 64-bit identifier that is hardcoded into each Fibre Channel HBA port or fabric device port. It serves as the unique address for an individual port within a Fibre Channel storage area network fabric, similar to a MAC address in Ethernet.

A World Wide Node Name (WWNN) identifies an entire Fibre Channel device, meaning multiple ports on that device will share the same WWNN, so it is not unique per individual port in the fabric.

While Fibre Channel uses addressing, the term "Fibre Channel MAC Address" is not the standard unique identifier for ports; the WWPN serves this purpose in Fibre Channel.