RFC 3720
Internet Small Computer Systems Interface (iSCSI)
Network Working Group J. Satran Request for Comments: 3720 K. Meth Category: Standards Track IBM C. Sapuntzakis Cisco Systems M. Chadalapaka Hewlett-Packard Co. E. Zeidner IBM April 2004 Internet Small Computer Systems Interface (iSCSI) Status of this Memo This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved.Abstract
This document describes a transport protocol for Internet Small Computer Systems Interface (iSCSI) that works on top of TCP. The iSCSI protocol aims to be fully compliant with the standardized SCSI architecture model. SCSI is a popular family of protocols that enable systems to communicate with I/O devices, especially storage devices. SCSI protocols are request/response application protocols with a common standardized architecture model and basic command set, as well as standardized command sets for different device classes (disks, tapes, media-changers etc.). As system interconnects move from the classical bus structure to a network structure, SCSI has to be mapped to network transport protocols. IP networks now meet the performance requirements of fast system interconnects and as such are good candidates to "carry" SCSI.
Table of Contents
1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . 9 2. Definitions and Acronyms. . . . . . . . . . . . . . . . . . . 10 2.1. Definitions. . . . . . . . . . . . . . . . . . . . . . 10 2.2. Acronyms . . . . . . . . . . . . . . . . . . . . . . . 14 2.3. Conventions. . . . . . . . . . . . . . . . . . . . . . 16 2.3.1. Word Rule. . . . . . . . . . . . . . . . . . 16 2.3.2. Half-Word Rule . . . . . . . . . . . . . . . 17 2.3.3. Byte Rule. . . . . . . . . . . . . . . . . . 17 3. Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . 17 3.1. SCSI Concepts. . . . . . . . . . . . . . . . . . . . . 17 3.2. iSCSI Concepts and Functional Overview . . . . . . . . 18 3.2.1. Layers and Sessions. . . . . . . . . . . . . 19 3.2.2. Ordering and iSCSI Numbering . . . . . . . . 19 3.2.2.1. Command Numbering and Acknowledging . . . . . . . . . . 20 3.2.2.2. Response/Status Numbering and Acknowledging . . . . . . . . . . 23 3.2.2.3. Data Sequencing . . . . . . . . 24 3.2.3. iSCSI Login. . . . . . . . . . . . . . . . . 24 3.2.4. iSCSI Full Feature Phase . . . . . . . . . . 25 3.2.4.1. Command Connection Allegiance . . 26 3.2.4.2. Data Transfer Overview. . . . . . 27 3.2.4.3. Tags and Integrity Checks . . . . 28 3.2.4.4. Task Management . . . . . . . . . 28 3.2.5. iSCSI Connection Termination . . . . . . . . 29 3.2.6. iSCSI Names. . . . . . . . . . . . . . . . . 29 3.2.6.1. iSCSI Name Properties . . . . . . 30 3.2.6.2. iSCSI Name Encoding . . . . . . . 31 3.2.6.3. iSCSI Name Structure. . . . . . . 32 3.2.6.3.1. Type "iqn." (iSCSI Qualified Name) . . . 32 3.2.6.3.2. Type "eui." (IEEE EUI-64 format). . . . 34 3.2.7. Persistent State . . . . . . . . . . . . . . 34 3.2.8. Message Synchronization and Steering . . . . 35 3.2.8.1. Sync/Steering and iSCSI PDU Length . . . . . . . . . . . . . 36 3.3. iSCSI Session Types. . . . . . . . . . . . . . . . . . 36 3.4. SCSI to iSCSI Concepts Mapping Model . . . . . . . . . 37 3.4.1. iSCSI Architecture Model . . . . . . . . . . 37 3.4.2. SCSI Architecture Model. . . . . . . . . . . 39 3.4.3. Consequences of the Model. . . . . . . . . . 41 3.4.3.1. I_T Nexus State . . . . . . . . . 42 3.5. Request/Response Summary . . . . . . . . . . . . . . . 42 3.5.1. Request/Response Types Carrying SCSI Payload 43 3.5.1.1. SCSI-Command . . . . . . . . . . 43
3.5.1.2. SCSI-Response . . . . . . . . . 43
3.5.1.3. Task Management Function Request. 44
3.5.1.4. Task Management Function Response 44
3.5.1.5. SCSI Data-Out and SCSI Data-In. . 44
3.5.1.6. Ready To Transfer (R2T) . . . . . 45
3.5.2. Requests/Responses carrying SCSI and iSCSI
Payload. . . . . . . . . . . . . . . . . . . 46
3.5.2.1. Asynchronous Message. . . . . . . 46
3.5.3. Requests/Responses Carrying iSCSI Only
Payload. . . . . . . . . . . . . . . . . . . 46
3.5.3.1. Text Request and Text Response. . 46
3.5.3.2. Login Request and Login Response. 47
3.5.3.3. Logout Request and Response . . . 47
3.5.3.4. SNACK Request . . . . . . . . . . 48
3.5.3.5. Reject. . . . . . . . . . . . . . 48
3.5.3.6. NOP-Out Request and NOP-In
Response . . . . . . . . . . . . 48
4. SCSI Mode Parameters for iSCSI. . . . . . . . . . . . . . . . 48
5. Login and Full Feature Phase Negotiation. . . . . . . . . . . 48
5.1. Text Format. . . . . . . . . . . . . . . . . . . . . . 50
5.2. Text Mode Negotiation. . . . . . . . . . . . . . . . . 53
5.2.1. List negotiations. . . . . . . . . . . . . . 56
5.2.2. Simple-value Negotiations. . . . . . . . . . 56
5.3. Login Phase. . . . . . . . . . . . . . . . . . . . . . 57
5.3.1. Login Phase Start. . . . . . . . . . . . . . 60
5.3.2. iSCSI Security Negotiation . . . . . . . . . 62
5.3.3. Operational Parameter Negotiation During
the Login Phase. . . . . . . . . . . . . . . 63
5.3.4. Connection Reinstatement . . . . . . . . . . 64
5.3.5. Session Reinstatement, Closure, and Timeout. 64
5.3.5.1. Loss of Nexus Notification . . . . 65
5.3.6. Session Continuation and Failure . . . . . . 65
5.4. Operational Parameter Negotiation Outside the Login
Phase. . . . . . . . . . . . . . . . . . . . . . . . . 66
6. iSCSI Error Handling and Recovery . . . . . . . . . . . . . . 67
6.1. Overview . . . . . . . . . . . . . . . . . . . . . . . 67
6.1.1. Background . . . . . . . . . . . . . . . . . 67
6.1.2. Goals. . . . . . . . . . . . . . . . . . . . 67
6.1.3. Protocol Features and State Expectations . . 68
6.1.4. Recovery Classes . . . . . . . . . . . . . . 69
6.1.4.1. Recovery Within-command . . . . . 69
6.1.4.2. Recovery Within-connection. . . . 70
6.1.4.3. Connection Recovery . . . . . . . 71
6.1.4.4. Session Recovery. . . . . . . . . 72
6.1.5. Error Recovery Hierarchy . . . . . . . . . . . 72
6.2. Retry and Reassign in Recovery . . . . . . . . . . . . 74
6.2.1. Usage of Retry . . . . . . . . . . . . . . . 74
6.2.2. Allegiance Reassignment. . . . . . . . . . . 75
6.3. Usage Of Reject PDU in Recovery. . . . . . . . . . . . 76
6.4. Connection Timeout Management. . . . . . . . . . . . . 76
6.4.1. Timeouts on Transport Exception Events . . . 77
6.4.2. Timeouts on Planned Decommissioning. . . . . 77
6.5. Implicit Termination of Tasks. . . . . . . . . . . . . 77
6.6. Format Errors. . . . . . . . . . . . . . . . . . . . . 78
6.7. Digest Errors. . . . . . . . . . . . . . . . . . . . . 78
6.8. Sequence Errors. . . . . . . . . . . . . . . . . . . . 80
6.9. SCSI Timeouts. . . . . . . . . . . . . . . . . . . . . 81
6.10. Negotiation Failures . . . . . . . . . . . . . . . . . 81
6.11. Protocol Errors. . . . . . . . . . . . . . . . . . . . 82
6.12. Connection Failures. . . . . . . . . . . . . . . . . . 82
6.13. Session Errors . . . . . . . . . . . . . . . . . . . . 83
7. State Transitions . . . . . . . . . . . . . . . . . . . . . . 84
7.1. Standard Connection State Diagrams . . . . . . . . . . 84
7.1.1. State Descriptions for Initiators and
Targets. . . . . . . . . . . . . . . . . . . 84
7.1.2. State Transition Descriptions for Initiators
and Targets. . . . . . . . . . . . . . . . . 85
7.1.3. Standard Connection State Diagram for an
Initiator. . . . . . . . . . . . . . . . . . 88
7.1.4. Standard Connection State Diagram for a
Target . . . . . . . . . . . . . . . . . . . 90
7.2. Connection Cleanup State Diagram for Initiators and
Targets. . . . . . . . . . . . . . . . . . . . . . . . 92
7.2.1. State Descriptions for Initiators and
Targets. . . . . . . . . . . . . . . . . . . 94
7.2.2. State Transition Descriptions for Initiators
and Targets. . . . . . . . . . . . . . . . . 94
7.3. Session State Diagrams . . . . . . . . . . . . . . . . 95
7.3.1. Session State Diagram for an Initiator . . . 95
7.3.2. Session State Diagram for a Target . . . . . 96
7.3.3. State Descriptions for Initiators and
Targets. . . . . . . . . . . . . . . . . . . 97
7.3.4. State Transition Descriptions for Initiators
and Targets. . . . . . . . . . . . . . . . . 98
8. Security Considerations . . . . . . . . . . . . . . . . . . . 99
8.1. iSCSI Security Mechanisms. . . . . . . . . . . . . . . 100
8.2. In-band Initiator-Target Authentication. . . . . . . . 100
8.2.1. CHAP Considerations. . . . . . . . . . . . . 101
8.2.2. SRP Considerations . . . . . . . . . . . . . 103
8.3. IPsec. . . . . . . . . . . . . . . . . . . . . . . . . 104
8.3.1. Data Integrity and Authentication. . . . . . 104
8.3.2. Confidentiality. . . . . . . . . . . . . . . 105
8.3.3. Policy, Security Associations, and
Cryptographic Key Management . . . . . . . . 105
9. Notes to Implementers . . . . . . . . . . . . . . . . . . . . 106
9.1. Multiple Network Adapters. . . . . . . . . . . . . . . 106
9.1.1. Conservative Reuse of ISIDs. . . . . . . . . 107
9.1.2. iSCSI Name, ISID, and TPGT Use . . . . . . . 107
9.2. Autosense and Auto Contingent Allegiance (ACA) . . . . 109
9.3. iSCSI Timeouts . . . . . . . . . . . . . . . . . . . . 109
9.4. Command Retry and Cleaning Old Command Instances . . . 110
9.5. Synch and Steering Layer and Performance . . . . . . . 110
9.6. Considerations for State-dependent Devices and
Long-lasting SCSI Operations . . . . . . . . . . . . . 111
9.6.1. Determining the Proper ErrorRecoveryLevel. . 112
10. iSCSI PDU Formats . . . . . . . . . . . . . . . . . . . . . . 112
10.1. iSCSI PDU Length and Padding . . . . . . . . . . . . . 113
10.2. PDU Template, Header, and Opcodes. . . . . . . . . . . 113
10.2.1. Basic Header Segment (BHS) . . . . . . . . . 114
10.2.1.1. I . . . . . . . . . . . . . . . . 115
10.2.1.2. Opcode. . . . . . . . . . . . . . 115
10.2.1.3. Final (F) bit . . . . . . . . . . 116
10.2.1.4. Opcode-specific Fields. . . . . . 116
10.2.1.5. TotalAHSLength. . . . . . . . . . 116
10.2.1.6. DataSegmentLength . . . . . . . . 116
10.2.1.7. LUN . . . . . . . . . . . . . . . 116
10.2.1.8. Initiator Task Tag. . . . . . . . 117
10.2.2. Additional Header Segment (AHS) . . . . . . . 117
10.2.2.1. AHSType . . . . . . . . . . . . . 117
10.2.2.2. AHSLength . . . . . . . . . . . . 117
10.2.2.3. Extended CDB AHS. . . . . . . . . 118
10.2.2.4. Bidirectional Expected Read-Data
Length AHS. . . . . . . . . . . . 118
10.2.3. Header Digest and Data Digest. . . . . . . . 118
10.2.4. Data Segment . . . . . . . . . . . . . . . . 119
10.3. SCSI Command . . . . . . . . . . . . . . . . . . . . . 119
10.3.1. Flags and Task Attributes (byte 1) . . . . . 120
10.3.2. CmdSN - Command Sequence Number. . . . . . . 120
10.3.3. ExpStatSN. . . . . . . . . . . . . . . . . . 120
10.3.4. Expected Data Transfer Length. . . . . . . . 121
10.3.5. CDB - SCSI Command Descriptor Block. . . . . 121
10.3.6. Data Segment - Command Data. . . . . . . . . 121
10.4. SCSI Response. . . . . . . . . . . . . . . . . . . . . 122
10.4.1. Flags (byte 1) . . . . . . . . . . . . . . . 123
10.4.2. Status . . . . . . . . . . . . . . . . . . . 123
10.4.3. Response . . . . . . . . . . . . . . . . . . 124
10.4.4. SNACK Tag. . . . . . . . . . . . . . . . . . 125
10.4.5. Residual Count . . . . . . . . . . . . . . . 125
10.4.6. Bidirectional Read Residual Count. . . . . . 125
10.4.7. Data Segment - Sense and Response Data
Segment. . . . . . . . . . . . . . . . . . . 125
10.4.7.1. SenseLength . . . . . . . . . . . 126
10.4.7.2. Sense Data. . . . . . . . . . . . 126
10.4.8. ExpDataSN. . . . . . . . . . . . . . . . . . 127
10.4.9. StatSN - Status Sequence Number. . . . . . . 127
10.4.10. ExpCmdSN - Next Expected CmdSN from this
Initiator. . . . . . . . . . . . . . . . . . 128
10.4.11. MaxCmdSN - Maximum CmdSN from this Initiator 128
10.5. Task Management Function Request . . . . . . . . . . . 129
10.5.1. Function . . . . . . . . . . . . . . . . . . 129
10.5.2. TotalAHSLength and DataSegmentLength . . . . 132
10.5.3. LUN. . . . . . . . . . . . . . . . . . . . . 132
10.5.4. Referenced Task Tag. . . . . . . . . . . . . 132
10.5.5. RefCmdSN . . . . . . . . . . . . . . . . . . 132
10.5.6. ExpDataSN. . . . . . . . . . . . . . . . . . 133
10.6. Task Management Function Response. . . . . . . . . . . 134
10.6.1. Response . . . . . . . . . . . . . . . . . . 134
10.6.2. Task Management Actions on Task Sets . . . . 136
10.6.3. TotalAHSLength and DataSegmentLength . . . . 137
10.7. SCSI Data-Out & SCSI Data-In . . . . . . . . . . . . . 137
10.7.1. F (Final) Bit. . . . . . . . . . . . . . . . 139
10.7.2. A (Acknowledge) Bit. . . . . . . . . . . . . 139
10.7.3. Flags (byte 1) . . . . . . . . . . . . . . . 140
10.7.4. Target Transfer Tag and LUN. . . . . . . . . 140
10.7.5. DataSN . . . . . . . . . . . . . . . . . . . 141
10.7.6. Buffer Offset. . . . . . . . . . . . . . . . 141
10.7.7. DataSegmentLength. . . . . . . . . . . . . . 141
10.8. Ready To Transfer (R2T). . . . . . . . . . . . . . . . 142
10.8.1. TotalAHSLength and DataSegmentLength . . . . 143
10.8.2. R2TSN. . . . . . . . . . . . . . . . . . . . 143
10.8.3. StatSN . . . . . . . . . . . . . . . . . . . 144
10.8.4. Desired Data Transfer Length and Buffer
Offset . . . . . . . . . . . . . . . . . . . 144
10.8.5. Target Transfer Tag. . . . . . . . . . . . . 144
10.9. Asynchronous Message . . . . . . . . . . . . . . . . . 145
10.9.1. AsyncEvent . . . . . . . . . . . . . . . . . 146
10.9.2. AsyncVCode . . . . . . . . . . . . . . . . . 147
10.9.3. LUN. . . . . . . . . . . . . . . . . . . . . 147
10.9.4. Sense Data and iSCSI Event Data. . . . . . . 148
10.9.4.1. SenseLength . . . . . . . . . . . 148
10.10. Text Request . . . . . . . . . . . . . . . . . . . . . 149
10.10.1. F (Final) Bit. . . . . . . . . . . . . . . . 150
10.10.2. C (Continue) Bit . . . . . . . . . . . . . . 150
10.10.3. Initiator Task Tag . . . . . . . . . . . . . 150
10.10.4. Target Transfer Tag. . . . . . . . . . . . . 150
10.10.5. Text . . . . . . . . . . . . . . . . . . . . 151
10.11. Text Response. . . . . . . . . . . . . . . . . . . . . 152
10.11.1. F (Final) Bit. . . . . . . . . . . . . . . . 152
10.11.2. C (Continue) Bit . . . . . . . . . . . . . . 153
10.11.3. Initiator Task Tag . . . . . . . . . . . . . 153
10.11.4. Target Transfer Tag. . . . . . . . . . . . . 153
10.11.5. StatSN . . . . . . . . . . . . . . . . . . . 154
10.11.6. Text Response Data . . . . . . . . . . . . . 154
10.12. Login Request. . . . . . . . . . . . . . . . . . . . . 154
10.12.1. T (Transit) Bit. . . . . . . . . . . . . . . 155
10.12.2. C (Continue) Bit . . . . . . . . . . . . . . 155
10.12.3. CSG and NSG. . . . . . . . . . . . . . . . . 156
10.12.4. Version. . . . . . . . . . . . . . . . . . . 156
10.12.4.1. Version-max. . . . . . . . . . . 156
10.12.4.2. Version-min. . . . . . . . . . . 156
10.12.5. ISID . . . . . . . . . . . . . . . . . . . . 157
10.12.6. TSIH . . . . . . . . . . . . . . . . . . . . 158
10.12.7. Connection ID - CID. . . . . . . . . . . . . 158
10.12.8. CmdSN. . . . . . . . . . . . . . . . . . . . 159
10.12.9. ExpStatSN. . . . . . . . . . . . . . . . . . 159
10.12.10. Login Parameters . . . . . . . . . . . . . . 159
10.13. Login Response . . . . . . . . . . . . . . . . . . . . 160
10.13.1. Version-max. . . . . . . . . . . . . . . . . 160
10.13.2. Version-active . . . . . . . . . . . . . . . 161
10.13.3. TSIH . . . . . . . . . . . . . . . . . . . . 161
10.13.4. StatSN . . . . . . . . . . . . . . . . . . . 161
10.13.5. Status-Class and Status-Detail . . . . . . . 161
10.13.6. T (Transit) Bit. . . . . . . . . . . . . . . 164
10.13.7. C (Continue) Bit . . . . . . . . . . . . . . 164
10.13.8. Login Parameters . . . . . . . . . . . . . . 164
10.14. Logout Request . . . . . . . . . . . . . . . . . . . . 165
10.14.1. Reason Code. . . . . . . . . . . . . . . . . 167
10.14.2. TotalAHSLength and DataSegmentLength . . . . 168
10.14.3. CID. . . . . . . . . . . . . . . . . . . . . 168
10.14.4. ExpStatSN. . . . . . . . . . . . . . . . . . 168
10.14.5. Implicit termination of tasks. . . . . . . . 168
10.15. Logout Response. . . . . . . . . . . . . . . . . . . . 169
10.15.1. Response . . . . . . . . . . . . . . . . . . 170
10.15.2. TotalAHSLength and DataSegmentLength . . . . 170
10.15.3. Time2Wait. . . . . . . . . . . . . . . . . . 170
10.15.4. Time2Retain. . . . . . . . . . . . . . . . . 170
10.16. SNACK Request. . . . . . . . . . . . . . . . . . . . . 171
10.16.1. Type . . . . . . . . . . . . . . . . . . . . 172
10.16.2. Data Acknowledgement . . . . . . . . . . . . 173
10.16.3. Resegmentation . . . . . . . . . . . . . . . 173
10.16.4. Initiator Task Tag . . . . . . . . . . . . . 174
10.16.5. Target Transfer Tag or SNACK Tag . . . . . . 174
10.16.6. BegRun . . . . . . . . . . . . . . . . . . . 174
10.16.7. RunLength. . . . . . . . . . . . . . . . . . 174
10.17. Reject . . . . . . . . . . . . . . . . . . . . . . . . 175
10.17.1. Reason . . . . . . . . . . . . . . . . . . . 176
10.17.2. DataSN/R2TSN . . . . . . . . . . . . . . . . 177
10.17.3. StatSN, ExpCmdSN and MaxCmdSN. . . . . . . . 177
10.17.4. Complete Header of Bad PDU . . . . . . . . . 177
10.18. NOP-Out. . . . . . . . . . . . . . . . . . . . . . . . 178
10.18.1. Initiator Task Tag . . . . . . . . . . . . . 179
10.18.2. Target Transfer Tag. . . . . . . . . . . . . 179
10.18.3. Ping Data. . . . . . . . . . . . . . . . . . 179
10.19. NOP-In . . . . . . . . . . . . . . . . . . . . . . . . 180
10.19.1. Target Transfer Tag. . . . . . . . . . . . . 181
10.19.2. StatSN . . . . . . . . . . . . . . . . . . . 181
10.19.3. LUN. . . . . . . . . . . . . . . . . . . . . 181
11. iSCSI Security Text Keys and Authentication Methods . . . . . 181
11.1. AuthMethod . . . . . . . . . . . . . . . . . . . . . . 182
11.1.1. Kerberos . . . . . . . . . . . . . . . . . . 184
11.1.2. Simple Public-Key Mechanism (SPKM) . . . . . 184
11.1.3. Secure Remote Password (SRP) . . . . . . . . 185
11.1.4. Challenge Handshake Authentication Protocol
(CHAP) . . . . . . . . . . . . . . . . . . . 186
12. Login/Text Operational Text Keys. . . . . . . . . . . . . . . 187
12.1. HeaderDigest and DataDigest. . . . . . . . . . . . . . 188
12.2. MaxConnections . . . . . . . . . . . . . . . . . . . . 190
12.3. SendTargets. . . . . . . . . . . . . . . . . . . . . . 191
12.4. TargetName . . . . . . . . . . . . . . . . . . . . . . 191
12.5. InitiatorName. . . . . . . . . . . . . . . . . . . . . 192
12.6. TargetAlias. . . . . . . . . . . . . . . . . . . . . . 192
12.7. InitiatorAlias . . . . . . . . . . . . . . . . . . . . 193
12.8. TargetAddress. . . . . . . . . . . . . . . . . . . . . 193
12.9. TargetPortalGroupTag . . . . . . . . . . . . . . . . . 194
12.10. InitialR2T . . . . . . . . . . . . . . . . . . . . . . 194
12.11. ImmediateData. . . . . . . . . . . . . . . . . . . . . 195
12.12. MaxRecvDataSegmentLength . . . . . . . . . . . . . . . 196
12.13. MaxBurstLength . . . . . . . . . . . . . . . . . . . . 196
12.14. FirstBurstLength . . . . . . . . . . . . . . . . . . . 197
12.15. DefaultTime2Wait . . . . . . . . . . . . . . . . . . . 197
12.16. DefaultTime2Retain . . . . . . . . . . . . . . . . . . 198
12.17. MaxOutstandingR2T. . . . . . . . . . . . . . . . . . . 198
12.18. DataPDUInOrder . . . . . . . . . . . . . . . . . . . . 198
12.19. DataSequenceInOrder. . . . . . . . . . . . . . . . . . 199
12.20. ErrorRecoveryLevel . . . . . . . . . . . . . . . . . . 199
12.21. SessionType. . . . . . . . . . . . . . . . . . . . . . 200
12.22. The Private or Public Extension Key Format . . . . . . 200
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 201
13.1. Naming Requirements. . . . . . . . . . . . . . . . . . 203
13.2. Mechanism Specification Requirements . . . . . . . . . 203
13.3. Publication Requirements . . . . . . . . . . . . . . . 203
13.4. Security Requirements. . . . . . . . . . . . . . . . . 203
13.5. Registration Procedure . . . . . . . . . . . . . . . . 204
13.5.1. Present the iSCSI extension item to the
Community. . . . . . . . . . . . . . . . . . 204
13.5.2. iSCSI extension item review and IESG
approval . . . . . . . . . . . . . . . . . . 204
13.5.3. IANA Registration. . . . . . . . . . . . . . 204
13.5.4. Standard iSCSI extension item-label format . 204
13.6. IANA Procedures for Registering iSCSI extension items. 205
References. . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
Appendix A. Sync and Steering with Fixed Interval Markers . . . . 209
A.1. Markers At Fixed Intervals . . . . . . . . . . . . . . 209
A.2. Initial Marker-less Interval . . . . . . . . . . . . . 210
A.3. Negotiation. . . . . . . . . . . . . . . . . . . . . . 210
A.3.1. OFMarker, IFMarker . . . . . . . . . . . . . 210
A.3.2. OFMarkInt, IFMarkInt . . . . . . . . . . . . 211
Appendix B. Examples . . . . . . . . . . . . . . . . . . . . . . 212
B.1. Read Operation Example . . . . . . . . . . . . . . . . 212
B.2. Write Operation Example. . . . . . . . . . . . . . . . 213
B.3. R2TSN/DataSN Use Examples. . . . . . . . . . . . . . . 214
B.4. CRC Examples . . . . . . . . . . . . . . . . . . . . . 217
Appendix C. Login Phase Examples . . . . . . . . . . . . . . . . 219
Appendix D. SendTargets Operation. . . . . . . . . . . . . . . . 229
Appendix E. Algorithmic Presentation of Error Recovery Classes . 233
E.1. General Data Structure and Procedure Description . . . 233
E.2. Within-command Error Recovery Algorithms . . . . . . . 234
E.2.1. Procedure Descriptions . . . . . . . . . . . 234
E.2.2. Initiator Algorithms . . . . . . . . . . . . 235
E.2.3. Target Algorithms. . . . . . . . . . . . . . 237
E.3. Within-connection Recovery Algorithms. . . . . . . . . 240
E.3.1. Procedure Descriptions . . . . . . . . . . . 240
E.3.2. Initiator Algorithms . . . . . . . . . . . . 241
E.3.3. Target Algorithms. . . . . . . . . . . . . . 243
E.4. Connection Recovery Algorithms . . . . . . . . . . . . 243
E.4.1. Procedure Descriptions . . . . . . . . . . . 243
E.4.2. Initiator Algorithms . . . . . . . . . . . . 244
E.4.3. Target Algorithms. . . . . . . . . . . . . . 246
Appendix F. Clearing Effects of Various Events on Targets. . . . 249
F.1. Clearing Effects on iSCSI Objects. . . . . . . . . . . 249
F.2. Clearing Effects on SCSI Objects . . . . . . . . . . . 253
Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . . . 254
Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . . . 256
Full Copyright Statement. . . . . . . . . . . . . . . . . . . . . 257
1. Introduction
The Small Computer Systems Interface (SCSI) is a popular family of
protocols for communicating with I/O devices, especially storage
devices. SCSI is a client-server architecture. Clients of a SCSI
interface are called "initiators". Initiators issue SCSI "commands"
to request services from components, logical units of a server known
as a "target". A "SCSI transport" maps the client-server SCSI
protocol to a specific interconnect. An Initiator is one endpoint of
a SCSI transport and a target is the other endpoint.
The SCSI protocol has been mapped over various transports, including Parallel SCSI, IPI, IEEE-1394 (firewire) and Fibre Channel. These transports are I/O specific and have limited distance capabilities. The iSCSI protocol defined in this document describes a means of transporting SCSI packets over TCP/IP (see [RFC791], [RFC793], [RFC1035], [RFC1122]), providing for an interoperable solution which can take advantage of existing Internet infrastructure, Internet management facilities, and address distance limitations.2. Definitions and Acronyms
2.1. Definitions
- Alias: An alias string can also be associated with an iSCSI Node. The alias allows an organization to associate a user-friendly string with the iSCSI Name. However, the alias string is not a substitute for the iSCSI Name. - CID (Connection ID): Connections within a session are identified by a connection ID. It is a unique ID for this connection within the session for the initiator. It is generated by the initiator and presented to the target during login requests and during logouts that close connections. - Connection: A connection is a TCP connection. Communication between the initiator and target occurs over one or more TCP connections. The TCP connections carry control messages, SCSI commands, parameters, and data within iSCSI Protocol Data Units (iSCSI PDUs). - iSCSI Device: A SCSI Device using an iSCSI service delivery subsystem. Service Delivery Subsystem is defined by [SAM2] as a transport mechanism for SCSI commands and responses. - iSCSI Initiator Name: The iSCSI Initiator Name specifies the worldwide unique name of the initiator. - iSCSI Initiator Node: The "initiator". The word "initiator" has been appropriately qualified as either a port or a device in the rest of the document when the context is ambiguous. All unqualified usages of "initiator" refer to an initiator port (or device) depending on the context. - iSCSI Layer: This layer builds/receives iSCSI PDUs and relays/receives them to/from one or more TCP connections that form an initiator-target "session".
- iSCSI Name: The name of an iSCSI initiator or iSCSI target.
- iSCSI Node: The iSCSI Node represents a single iSCSI initiator or
iSCSI target. There are one or more iSCSI Nodes within a Network
Entity. The iSCSI Node is accessible via one or more Network
Portals. An iSCSI Node is identified by its iSCSI Name. The
separation of the iSCSI Name from the addresses used by and for the
iSCSI Node allows multiple iSCSI Nodes to use the same address, and
the same iSCSI Node to use multiple addresses.
- iSCSI Target Name: The iSCSI Target Name specifies the worldwide
unique name of the target.
- iSCSI Target Node: The "target".
- iSCSI Task: An iSCSI task is an iSCSI request for which a response
is expected.
- iSCSI Transfer Direction: The iSCSI transfer direction is defined
with regard to the initiator. Outbound or outgoing transfers are
transfers from the initiator to the target, while inbound or
incoming transfers are from the target to the initiator.
- ISID: The initiator part of the Session Identifier. It is
explicitly specified by the initiator during Login.
- I_T nexus: According to [SAM2], the I_T nexus is a relationship
between a SCSI Initiator Port and a SCSI Target Port. For iSCSI,
this relationship is a session, defined as a relationship between
an iSCSI Initiator's end of the session (SCSI Initiator Port) and
the iSCSI Target's Portal Group. The I_T nexus can be identified
by the conjunction of the SCSI port names; that is, the I_T nexus
identifier is the tuple (iSCSI Initiator Name + ',i,'+ ISID, iSCSI
Target Name + ',t,'+ Portal Group Tag).
- Network Entity: The Network Entity represents a device or gateway
that is accessible from the IP network. A Network Entity must have
one or more Network Portals, each of which can be used to gain
access to the IP network by some iSCSI Nodes contained in that
Network Entity.
- Network Portal: The Network Portal is a component of a Network
Entity that has a TCP/IP network address and that may be used by an
iSCSI Node within that Network Entity for the connection(s) within
one of its iSCSI sessions. A Network Portal in an initiator is
identified by its IP address. A Network Portal in a target is
identified by its IP address and its listening TCP port.
- Originator: In a negotiation or exchange, the party that initiates
the negotiation or exchange.
- PDU (Protocol Data Unit): The initiator and target divide their
communications into messages. The term "iSCSI protocol data unit"
(iSCSI PDU) is used for these messages.
- Portal Groups: iSCSI supports multiple connections within the same
session; some implementations will have the ability to combine
connections in a session across multiple Network Portals. A Portal
Group defines a set of Network Portals within an iSCSI Network
Entity that collectively supports the capability of coordinating a
session with connections spanning these portals. Not all Network
Portals within a Portal Group need participate in every session
connected through that Portal Group. One or more Portal Groups may
provide access to an iSCSI Node. Each Network Portal, as utilized
by a given iSCSI Node, belongs to exactly one portal group within
that node.
- Portal Group Tag: This 16-bit quantity identifies a Portal Group
within an iSCSI Node. All Network Portals with the same portal
group tag in the context of a given iSCSI Node are in the same
Portal Group.
- Recovery R2T: An R2T generated by a target upon detecting the loss
of one or more Data-Out PDUs through one of the following means: a
digest error, a sequence error, or a sequence reception timeout. A
recovery R2T carries the next unused R2TSN, but requests all or
part of the data burst that an earlier R2T (with a lower R2TSN) had
already requested.
- Responder: In a negotiation or exchange, the party that responds to
the originator of the negotiation or exchange.
- SCSI Device: This is the SAM2 term for an entity that contains one
or more SCSI ports that are connected to a service delivery
subsystem and supports a SCSI application protocol. For example, a
SCSI Initiator Device contains one or more SCSI Initiator Ports and
zero or more application clients. A Target Device contains one or
more SCSI Target Ports and one or more device servers and
associated logical units. For iSCSI, the SCSI Device is the
component within an iSCSI Node that provides the SCSI
functionality. As such, there can be at most, one SCSI Device
within a given iSCSI Node. Access to the SCSI Device can only be
achieved in an iSCSI normal operational session. The SCSI Device
Name is defined to be the iSCSI Name of the node.
- SCSI Layer: This builds/receives SCSI CDBs (Command Descriptor
Blocks) and relays/receives them with the remaining command execute
[SAM2] parameters to/from the iSCSI Layer.
- Session: The group of TCP connections that link an initiator with a
target form a session (loosely equivalent to a SCSI I-T nexus).
TCP connections can be added and removed from a session. Across
all connections within a session, an initiator sees one and the
same target.
- SCSI Initiator Port: This maps to the endpoint of an iSCSI normal
operational session. An iSCSI normal operational session is
negotiated through the login process between an iSCSI initiator
node and an iSCSI target node. At successful completion of this
process, a SCSI Initiator Port is created within the SCSI Initiator
Device. The SCSI Initiator Port Name and SCSI Initiator Port
Identifier are both defined to be the iSCSI Initiator Name together
with (a) a label that identifies it as an initiator port
name/identifier and (b) the ISID portion of the session identifier.
- SCSI Port: This is the SAM2 term for an entity in a SCSI Device
that provides the SCSI functionality to interface with a service
delivery subsystem. For iSCSI, the definition of the SCSI
Initiator Port and the SCSI Target Port are different.
- SCSI Port Name: A name made up as UTF-8 [RFC2279] characters and
includes the iSCSI Name + 'i' or 't' + ISID or Portal Group Tag.
- SCSI Target Port: This maps to an iSCSI Target Portal Group.
- SCSI Target Port Name and SCSI Target Port Identifier: These are
both defined to be the iSCSI Target Name together with (a) a label
that identifies it as a target port name/identifier and (b) the
portal group tag.
- SSID (Session ID): A session between an iSCSI initiator and an
iSCSI target is defined by a session ID that is a tuple composed of
an initiator part (ISID) and a target part (Target Portal Group
Tag). The ISID is explicitly specified by the initiator at session
establishment. The Target Portal Group Tag is implied by the
initiator through the selection of the TCP endpoint at connection
establishment. The TargetPortalGroupTag key must also be returned
by the target as a confirmation during connection establishment
when TargetName is given.
- Target Portal Group Tag: A numerical identifier (16-bit) for an
iSCSI Target Portal Group.
- TSIH (Target Session Identifying Handle): A target assigned tag for
a session with a specific named initiator. The target generates it
during session establishment. Its internal format and content are
not defined by this protocol, except for the value 0 that is
reserved and used by the initiator to indicate a new session. It
is given to the target during additional connection establishment
for the same session.
2.2. Acronyms
Acronym Definition
------------------------------------------------------------
3DES Triple Data Encryption Standard
ACA Auto Contingent Allegiance
AEN Asynchronous Event Notification
AES Advanced Encryption Standard
AH Additional Header (not the IPsec AH!)
AHS Additional Header Segment
API Application Programming Interface
ASC Additional Sense Code
ASCII American Standard Code for Information Interchange
ASCQ Additional Sense Code Qualifier
BHS Basic Header Segment
CBC Cipher Block Chaining
CD Compact Disk
CDB Command Descriptor Block
CHAP Challenge Handshake Authentication Protocol
CID Connection ID
CO Connection Only
CRC Cyclic Redundancy Check
CRL Certificate Revocation List
CSG Current Stage
CSM Connection State Machine
DES Data Encryption Standard
DNS Domain Name Server
DOI Domain of Interpretation
DVD Digital Versatile Disk
ESP Encapsulating Security Payload
EUI Extended Unique Identifier
FFP Full Feature Phase
FFPO Full Feature Phase Only
FIM Fixed Interval Marker
Gbps Gigabits per Second
HBA Host Bus Adapter
HMAC Hashed Message Authentication Code
I_T Initiator_Target
I_T_L Initiator_Target_LUN
IANA Internet Assigned Numbers Authority
ID Identifier
IDN Internationalized Domain Name
IEEE Institute of Electrical & Electronics Engineers
IETF Internet Engineering Task Force
IKE Internet Key Exchange
I/O Input - Output
IO Initialize Only
IP Internet Protocol
IPsec Internet Protocol Security
IPv4 Internet Protocol Version 4
IPv6 Internet Protocol Version 6
IQN iSCSI Qualified Name
ISID Initiator Session ID
ITN iSCSI Target Name
ITT Initiator Task Tag
KRB5 Kerberos V5
LFL Lower Functional Layer
LTDS Logical-Text-Data-Segment
LO Leading Only
LU Logical Unit
LUN Logical Unit Number
MAC Message Authentication Codes
NA Not Applicable
NIC Network Interface Card
NOP No Operation
NSG Next Stage
OS Operating System
PDU Protocol Data Unit
PKI Public Key Infrastructure
R2T Ready To Transfer
R2TSN Ready To Transfer Sequence Number
RDMA Remote Direct Memory Access
RFC Request For Comments
SAM SCSI Architecture Model
SAM2 SCSI Architecture Model - 2
SAN Storage Area Network
SCSI Small Computer Systems Interface
SN Sequence Number
SNACK Selective Negative Acknowledgment - also
Sequence Number Acknowledgement for data
SPKM Simple Public-Key Mechanism
SRP Secure Remote Password
SSID Session ID
SW Session Wide
TCB Task Control Block
TCP Transmission Control Protocol
TPGT Target Portal Group Tag
TSIH Target Session Identifying Handle
TTT Target Transfer Tag UFL Upper Functional Layer ULP Upper Level Protocol URN Uniform Resource Names [RFC2396] UTF Universal Transformation Format WG Working Group2.3. Conventions
In examples, "I->" and "T->" show iSCSI PDUs sent by the initiator and target respectively. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119]. iSCSI messages - PDUs - are represented by diagrams as in the following example: Byte/ 0 | 1 | 2 | 3 | / | | | | |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7| +---------------+---------------+---------------+---------------+ 0| Basic Header Segment (BHS) | +---------------+---------------+---------------+---------------+ ---------- +| | +---------------+---------------+---------------+---------------+ The diagrams include byte and bit numbering. The following representation and ordering rules are observed in this document: - Word Rule - Half-word Rule - Byte Rule2.3.1. Word Rule
A word holds four consecutive bytes. Whenever a word has numeric content, it is considered an unsigned number in base 2 positional representation with the lowest numbered byte (e.g., byte 0) bit 0 representing 2**31 and bit 1 representing 2**30 through lowest numbered byte + 3 (e.g., byte 3) bit 7 representing 2**0. Decimal and hexadecimal representation of word values map this representation to decimal or hexadecimal positional notation.
2.3.2. Half-Word Rule
A half-word holds two consecutive bytes. Whenever a half-word has numeric content it is considered an unsigned number in base 2 positional representation with the lowest numbered byte (e.g., byte 0), bit 0 representing 2**15 and bit 1 representing 2**14 through lowest numbered byte + 1 (e.g., byte 1), bit 7 representing 2**0. Decimal and hexadecimal representation of half-word values map this representation to decimal or hexadecimal positional notation.2.3.3. Byte Rule
For every PDU, bytes are sent and received in increasing numbered order (network order). Whenever a byte has numerical content, it is considered an unsigned number in base 2 positional representation with bit 0 representing 2**7 and bit 1 representing 2**6 through bit 7 representing 2**0.
(page 17 continued on part 2)
