Network Working Group                                         M. Krueger
Request for Comments: 3347                                    R. Haagens
Category: Informational                      Hewlett-Packard Corporation
                                                          C. Sapuntzakis
                                                                Stanford
                                                                M. Bakke
                                                           Cisco Systems
                                                               July 2002


  Small Computer Systems Interface protocol over the Internet (iSCSI)
                Requirements and Design Considerations

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

   This document specifies the requirements iSCSI and its related
   infrastructure should satisfy and the design considerations guiding
   the iSCSI protocol development efforts.  In the interest of timely
   adoption of the iSCSI protocol, the IPS group has chosen to focus the
   first version of the protocol to work with the existing SCSI
   architecture and commands, and the existing TCP/IP transport layer.
   Both these protocols are widely-deployed and well-understood.  The
   thought is that using these mature protocols will entail a minimum of
   new invention, the most rapid possible adoption, and the greatest
   compatibility with Internet architecture, protocols, and equipment.

Conventions used in this document

   This document describes the requirements for a protocol design, but
   does not define a protocol standard.  Nevertheless, 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 RFC-2119 [2].








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Table of Contents

   1.   Introduction.................................................2
   2.   Summary of Requirements......................................3
   3.   iSCSI Design Considerations..................................7
   3.1. General Discussion...........................................7
   3.2. Performance/Cost.............................................9
   3.3. Framing.....................................................11
   3.4. High bandwidth, bandwidth aggregation.......................13
   4.   Ease of implementation/complexity of protocol...............14
   5.   Reliability and Availability................................15
   5.1. Detection of Data Corruption................................15
   5.2. Recovery....................................................15
   6.   Interoperability............................................16
   6.1. Internet infrastructure.....................................16
   6.2. SCSI........................................................16
   7.   Security Considerations.....................................18
   7.1. Extensible Security.........................................18
   7.2. Authentication..............................................18
   7.3. Data Integrity..............................................19
   7.4. Data Confidentiality........................................19
   8.   Management..................................................19
   8.1. Naming......................................................20
   8.2. Discovery...................................................21
   9.   Internet Accessibility......................................21
   9.1. Denial of Service...........................................21
   9.2. NATs, Firewalls and Proxy servers...........................22
   9.3. Congestion Control and Transport Selection..................22
   10.  Definitions.................................................22
   11.  References..................................................23
   12.  Acknowledgements............................................24
   13.  Author's Addresses..........................................25
   14.  Full Copyright Statement....................................26

1. Introduction

   The IP Storage Working group is chartered with developing
   comprehensive technology to transport block storage data over IP
   protocols.  This effort includes a protocol to transport the Small
   Computer Systems Interface (SCSI) protocol over the Internet (iSCSI).
   The initial version of the iSCSI protocol will define a mapping of
   SCSI transport protocol over TCP/IP so that SCSI storage controllers
   (principally disk and tape arrays and libraries) can be attached to
   IP networks, notably Gigabit Ethernet (GbE) and 10 Gigabit Ethernet
   (10 GbE).






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RFC 3347      iSCSI Requirements and Design Considerations     July 2002


   The iSCSI protocol is a mapping of SCSI to TCP, and constitutes a
   "SCSI transport" as defined by the ANSI T10 document SCSI SAM-2
   document [SAM2, p. 3, "Transport Protocols"].

2. Summary of Requirements

   The iSCSI standard:

   From section 3.2 Performance/Cost:

      MUST allow implementations to equal or improve on the current
      state of the art for SCSI interconnects.

      MUST enable cost competitive implementations.

      SHOULD minimize control overhead to enable low delay
      communications.

      MUST provide high bandwidth and bandwidth aggregation.

      MUST have low host CPU utilizations, equal to or better than
      current technology.

      MUST be possible to build I/O adapters that handle the entire SCSI
      task.

      SHOULD permit direct data placement architectures.

      MUST NOT impose complex operations on host software.

      MUST provide for full utilization of available link bandwidth.

      MUST allow an implementation to exploit parallelism (multiple
      connections) at the device interfaces and within the interconnect
      fabric.

   From section 3.4 High Bandwidth/Bandwidth Aggregation:

      MUST operate over a single TCP connection.

      SHOULD support 'connection binding', and it MUST be optional to
      implement.

   From section 4 Ease of Implementation/Complexity of Protocol:

      SHOULD keep the protocol simple.

      SHOULD minimize optional features.



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      MUST specify feature negotiation at session establishment (login).

      MUST operate correctly when no optional features are negotiated as
      well as when individual option negotions are unsuccessful.

   From section 5.1 Detection of Data Corruption:

      MUST support a data integrity check format for use in digest
      generation.

      MAY use separate digest for data and headers.

      iSCSI header format SHOULD be extensible to include other data
      integrity digest calculation methods.

   From section 5.2 Recovery:

      MUST specify mechanisms to recover in a timely fashion from
      failures on the initiator, target, or connecting infrastructure.

      MUST specify recovery methods for non-idempotent requests.

      SHOULD take into account fail-over schemes for mirrored targets or
      highly available storage configurations.

      SHOULD provide a method for sessions to be gracefully terminated
      and restarted that can be initiated by either the initiator or
      target.

   From section 6 Interoperability:

      iSCSI protocol document MUST be clear and unambiguous.

   From section 6.1 Internet Infrastructure:

      MUST:
      -- be compatible with both IPv4 and IPv6
      -- use TCP connections conservatively, keeping in mind there may
         be many other users of TCP on a given machine.

      MUST NOT require changes to existing Internet protocols.

      SHOULD minimize required changes to existing TCP/IP
      implementations.

      MUST be designed to allow future substitution of SCTP (for TCP) as
      an IP transport protocol with minimal changes to iSCSI protocol
      operation, protocol data unit (PDU) structures and formats.



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   From section 6.2 SCSI:

      Any feature SAM2 requires in a valid transport mapping MUST be
      specified by iSCSI.

      MUST specify strictly ordered delivery of SCSI commands over an
      iSCSI session between an initiator/target pair.

      The command ordering mechanism SHOULD seek to minimize the amount
      of communication necessary across multiple adapters doing
      transport off-load.

      MUST specify for each feature whether it is OPTIONAL, RECOMMENDED
      or REQUIRED to implement and/or use.

      MUST NOT require changes to the SCSI-3 command sets and SCSI
      client code except except where SCSI specifications point to
      "transport dependent" fields and behavior.

      SHOULD track changes to SCSI and the SCSI Architecture Model.

      MUST be capable of supporting all SCSI-3 command sets and device
      types.

      SHOULD support ACA implementation.

      MUST allow for the construction of gateways to other SCSI
      transports

      MUST reliably transport SCSI commands from the initiator to the
      target.

      MUST correctly deal with iSCSI packet drop, duplication,
      corruption, stale packets, and re-ordering.

   From section 7.1 Extensible Security:

      SHOULD require minimal configuration and overhead in the insecure
      operation.

      MUST provide for strong authentication when increased security is
      required.

      SHOULD allow integration of new security mechanisms without
      breaking backwards compatible operation.






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   From section 7.2 Authentication:

      MAY support various levels of authentication security.

      MUST support private authenticated login.

      iSCSI authenticated login MUST be resilient against attacks.

      MUST support data origin authentication of its communications;
      data origin authentication MAY be optional to use.

   From section 7.3 Data Integrity:

      SHOULD NOT preclude use of additional data integrity protection
      protocols (IPSec, TLS).

   From section 7.4 Data Confidentiality:

      MUST provide for the use of a data encryption protocol such as TLS
      or IPsec ESP to provide data confidentiality between iSCSI
      endpoints

   From section 8 Management:

      SHOULD be manageable using standard IP-based management protocols.

      iSCSI protocol document MUST NOT define the management
      architecture for iSCSI, or make explicit references to management
      objects such as MIB variables.

   From section 8.1 Naming:

      MUST support the naming architecture of SAM-2. The means by which
      an iSCSI resource is located MUST use or extend existing Internet
      standard resource location methods.

      MUST provide a means of identifying iSCSI targets by a unique
      identifier that is independent of the path on which it is found.

      The format for the iSCSI names MUST use existing naming
      authorities.

      An iSCSI name SHOULD be a human readable string in an
      international character set encoding.

      Standard Internet lookup services SHOULD be used to resolve iSCSI
      names.




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      SHOULD deal with the complications of the new SCSI security
      architecture.

      iSCSI naming architecture MUST address support of SCSI 3rd party
      operations such as EXTENDED COPY.

   From section 8.2 Discovery:

      MUST have no impact on the use of current IP network discovery
      techniques.

      MUST provide some means of determining whether an iSCSI service is
      available through an IP address.

      SCSI protocol-dependent techniques SHOULD be used for further
      discovery beyond the iSCSI layer.

      MUST provide a method of discovering, given an IP end point on its
      well-known port, the list of SCSI targets available to the
      requestor.  The use of this discovery service MUST be optional.

   From section 9 Internet Accessability.

      SHOULD be scrutinized for denial of service issues and they should