iSCSI PDU Formats: iSCSI uses one general PDU format for many purposes. The specific format of an iSCSI PDU is determined by the type of PDU. RFC 7143 defines numerous PDU types to facilitate communication between initiators and targets.

The primary PDU types include:

• login request
• login response
• SCSI command
• SCSI response
• data-out
• data-in
• ready to transfer (R2T)
• selective negative acknowledgment (SNACK) request
• task management function (TMF) request
• TMF response, and reject.

All iSCSI PDUs begin with a basic header segment (BHS). The BHS may be followed by one or more additional header segments (AHS), a header-digest, a data segment, or a data-digest. The data-digest may be present only if the data segment is present.

• You must follow the iSCSI data flow using the initiator task tag (ITT) field.

Initiator Task Tag (ITT)—. Storage Networking Protocol Fundamentals This is 32 bits long. It contains a tag assigned by the initiator. An ITT is assigned to each iSCSI task. Likewise, an ITT is assigned to each SCSI task. A SCSI task can represent a single SCSI command or multiple linked commands. Each SCSI command can have many SCSI activities associated with it. A SCSI task encompasses all activities associated with a SCSI command or multiple linked commands. Likewise, an ITT that represents a SCSI task also encompasses all associated activities of the SCSI command(s). An ITT value is unique only within the context of the current session. The iSCSI ITT is similar in function to the FC fully qualified exchange identifier (FQXID).

• You must filter in wireshark using the field iscsi.initiatortasktag == 0xa1500f4a to follow the read or write operations.

• You can create a flow graph with wirekshark

• Check - Limit do display filter