iSCSI, a block-level storage, uses an IP to send the SCSI commands over TCP/IP networks. iSCSI works in such a way that the clients, known as initiators, use the IP protocol to send SCSI commands called Command Descriptor Blocks (CDBs) to storage devices known as targets. In SANs, the logical unit number (LUN) represents a logical disk. In an iSCSI, TCP port 860 is reserved for the iSCSI system port, whereas TCP port 3260 represents iSCSI's default port.