This enumerated INTEGER (unknown, ethernet, fibre, infiniband, sas, and other values) indicates the subtype of switch module installed, as reported by the module's main application firmware. An admin compares this against the switch subtype reported by the module's other firmware layer to confirm both layers agree on what kind of module is physically installed, since a mismatch can indicate a firmware corruption or a card that was swapped without a matching firmware reload. For example, smMainAppVpdSwitchSubType returning infiniband(6) tells the admin the switch bay currently holds an InfiniBand module rather than the Ethernet module that was there before a hardware swap.