This SnmpAdminString field holds the Distinguished Name of the actual object (a port, VSAN, or endpoint) that this FC monitor source reference identifies as the traffic source. For a linking record identifying exactly which object (port, VSAN, or endpoint) is supplying the mirrored traffic for an FC monitoring session, this is the concrete pointer that lets UCS Manager resolve an abstract 'source' reference in a monitoring session down to one specific, real hardware object whose frames get copied. In a working session this resolves to the DN of a real FC port or VSAN object; a blank value here would mean the source reference is currently unresolved, and the session can't actually be capturing anything.