Combinations of host ports and storage ports (e.g., I-T pairs) on a storage network that are zoned but not masked may be determined, without accessing a switch or network administrator. Heartbeat communications (heartbeats) may be transmitted from host systems to each storage device of a storage system of which the host system is aware, along the one or more I/O paths of which the host is aware to the storage port of the I/O path. The storage devices may include one or more nominal devices defined for I-T pairs for which I/O connectivity has not been defined for any storage devices. The storage system may maintain a master heartbeat (heartbeat) table that may include a plurality of entries, each entry corresponding to a combination of a host port, storage port and storage device, and storing a time stamp value for a most recent heartbeat received for the combination.