Network Working Group                                           J. Tseng
Request for Comments: 4171                           Riverbed Technology
Category: Standards Track                                     K. Gibbons
                                                      McDATA Corporation
                                                           F. Travostino
                                                                  Nortel
                                                             C. Du Laney
                                             Rincon Research Corporation
                                                                J. Souza
                                                               Microsoft
                                                          September 2005


                 Internet Storage Name Service (iSNS)

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 (2005).

Abstract

   This document specifies the Internet Storage Name Service (iSNS)
   protocol, used for interaction between iSNS servers and iSNS clients,
   which facilitates automated discovery, management, and configuration
   of iSCSI and Fibre Channel devices (using iFCP gateways) on a TCP/IP
   network.  iSNS provides intelligent storage discovery and management
   services comparable to those found in Fibre Channel networks,
   allowing a commodity IP network to function in a capacity similar to
   that of a storage area network.  iSNS facilitates a seamless
   integration of IP and Fibre Channel networks due to its ability to
   emulate Fibre Channel fabric services and to manage both iSCSI and
   Fibre Channel devices.  iSNS thereby provides value in any storage
   network comprised of iSCSI devices, Fibre Channel devices (using iFCP
   gateways), or any combination thereof.









Tseng, et al.              Standards Track                      [Page 1]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


Table of Contents

   1.  Introduction................................................... 6
       1.1.  Conventions Used in This Document........................ 6
       1.2.  Purpose of This Document................................. 6
   2.  iSNS Overview.................................................. 6
       2.1.  iSNS Architectural Components ........................... 7
             2.1.1.  iSNS Protocol (iSNSP) ........................... 7
             2.1.2.  iSNS Client...................................... 7
             2.1.3.  iSNS Server...................................... 7
             2.1.4.  iSNS Database ................................... 7
             2.1.5.  iSCSI............................................ 7
             2.1.6.  iFCP............................................. 7
       2.2.  iSNS Functional Overview................................. 8
             2.2.1.  Name Registration Service........................ 8
             2.2.2.  Discovery Domain and Login Control Service....... 8
             2.2.3.  State Change Notification Service............... 10
             2.2.4.  Open Mapping between
                     Fibre Channel and iSCSI Devices................. 11
       2.3.  iSNS Usage Model........................................ 11
             2.3.1.  iSCSI Initiator................................. 12
             2.3.2.  iSCSI Target.................................... 12
             2.3.3.  iSCSI-FC Gateway................................ 12
             2.3.4.  iFCP Gateway.................................... 12
             2.3.5.  Management Station.............................. 12
       2.4.  Administratively Controlled iSNS Settings............... 13
       2.5.  iSNS Server Discovery .................................. 14
             2.5.1.  Service Location Protocol (SLP)................. 14
             2.5.2.  Dynamic Host Configuration Protocol (DHCP)...... 14
             2.5.3.  iSNS Heartbeat Message.......................... 14
       2.6.  iSNS and Network Address Translation (NAT).............. 14
       2.7.  Transfer of iSNS Database Records between iSNS Servers.. 15
       2.8.  Backup iSNS Servers..................................... 17
       2.9.  Transport Protocols..................................... 19
             2.9.1.  Use of TCP for iSNS Communication............... 19
             2.9.2.  Use of UDP for iSNS Communication............... 20
             2.9.3.  iSNS Multicast and Broadcast Messages........... 20
       2.10. Simple Network Management Protocol (SNMP) Requirements.. 21
   3.  iSNS Object Model............................................. 21
       3.1.  Network Entity Object .................................. 22
       3.2.  Portal Object .......................................... 22
       3.3.  Storage Node Object..................................... 22
       3.4.  Portal Group Object..................................... 23
       3.5.  FC Device Object........................................ 24
       3.6.  Discovery Domain Object................................. 24
       3.7.  Discovery Domain Set Object............................. 24
       3.8.  iSNS Database Model..................................... 24
   4.  iSNS Implementation Requirements.............................. 25



Tseng, et al.              Standards Track                      [Page 2]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


       4.1.  iSCSI Requirements...................................... 25
             4.1.1.  Required Attributes for Support of iSCSI........ 26
             4.1.2.  Examples: iSCSI Object Model Diagrams........... 28
             4.1.3.  Required Commands and
                     Response Messages for Support of iSCSI.......... 30
       4.2.  iFCP Requirements....................................... 31
             4.2.1.  Required Attributes for Support of iFCP......... 31
             4.2.2.  Example: iFCP Object Model Diagram.............. 32
             4.2.3.  Required Commands and
                     Response Messages for Support of iFCP........... 34
   5.  iSNSP Message Format.......................................... 35
       5.1.  iSNSP PDU Header........................................ 35
             5.1.1.  iSNSP Version................................... 36
             5.1.2.  iSNSP Function ID............................... 36
             5.1.3.  iSNSP PDU Length................................ 36
             5.1.4.  iSNSP Flags..................................... 36
             5.1.5.  iSNSP Transaction ID............................ 36
             5.1.6.  iSNSP Sequence ID............................... 37
       5.2.  iSNSP Message Segmentation and Reassembly............... 37
       5.3.  iSNSP PDU Payload....................................... 37
             5.3.1.  Attribute Value 4-Byte Alignment................ 38
       5.4.  iSNSP Response Status Codes............................. 39
       5.5.  Authentication for iSNS Multicast and Broadcast Messages 39
       5.6.  Registration and Query Messages......................... 41
             5.6.1.  Source Attribute................................ 42
             5.6.2.  Message Key Attributes.......................... 42
             5.6.3.  Delimiter Attribute............................. 42
             5.6.4.  Operating Attributes............................ 43
             5.6.5.  Registration and Query Request Message Types ... 44
       5.7.  Response Messages....................................... 66
             5.7.1.  Status Code..................................... 66
             5.7.2.  Message Key Attributes in Response.............. 66
             5.7.3.  Delimiter Attribute in Response................. 67
             5.7.4.  Operating Attributes in Response................ 67
             5.7.5.  Registration and Query Response Message Type.... 67
       5.8.  Vendor-Specific Messages................................ 72
   6.  iSNS Attributes............................................... 73
       6.1.  iSNS Attribute Summary.................................. 73
       6.2.  Entity Identifier-Keyed Attributes...................... 76
             6.2.1.  Entity Identifier (EID)......................... 76
             6.2.2.  Entity Protocol................................. 76
             6.2.3.  Management IP Address .......................... 77
             6.2.4.  Entity Registration Timestamp .................. 77
             6.2.5.  Protocol Version Range.......................... 77
             6.2.6.  Registration Period............................. 78
             6.2.7.  Entity Index.................................... 78
             6.2.8.  Entity Next Index............................... 79
             6.2.9.  Entity ISAKMP Phase-1 Proposals................. 79



Tseng, et al.              Standards Track                      [Page 3]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


             6.2.10. Entity Certificate.............................. 79
       6.3.  Portal-Keyed Attributes................................. 80
             6.3.1.  Portal IP Address............................... 80
             6.3.2.  Portal TCP/UDP Port............................. 80
             6.3.3.  Portal Symbolic Name............................ 80
             6.3.4.  Entity Status Inquiry Interval.................. 81
             6.3.5.  ESI Port........................................ 82
             6.3.6.  Portal Index.................................... 82
             6.3.7.  SCN Port........................................ 82
             6.3.8.  Portal Next Index............................... 83
             6.3.9.  Portal Security Bitmap.......................... 83
             6.3.10. Portal ISAKMP Phase-1 Proposals................. 84
             6.3.11. Portal ISAKMP Phase-2 Proposals................. 84
             6.3.12. Portal Certificate.............................. 84
       6.4.  iSCSI Node-Keyed Attributes............................. 84
             6.4.1.  iSCSI Name...................................... 85
             6.4.2.  iSCSI Node Type................................. 85
             6.4.3.  iSCSI Node Alias................................ 86
             6.4.4.  iSCSI Node SCN Bitmap .......................... 86
             6.4.5.  iSCSI Node Index................................ 87
             6.4.6.  WWNN Token...................................... 87
             6.4.7.  iSCSI Node Next Index .......................... 89
             6.4.8.  iSCSI AuthMethod................................ 89
       6.5.  Portal Group (PG) Object-Keyed Attributes............... 89
             6.5.1.  Portal Group iSCSI Name......................... 90
             6.5.2.  PG Portal IP Addr............................... 90
             6.5.3.  PG Portal TCP/UDP Port.......................... 90
             6.5.4.  Portal Group Tag (PGT).......................... 90
             6.5.5.  Portal Group Index.............................. 90
             6.5.6.  Portal Group Next Index......................... 91
       6.6.  FC Port Name-Keyed Attributes .......................... 91
             6.6.1.  FC Port Name (WWPN)............................. 91
             6.6.2.  Port ID (FC_ID)................................. 91
             6.6.3.  FC Port Type.................................... 92
             6.6.4.  Symbolic Port Name.............................. 92
             6.6.5.  Fabric Port Name (FWWN)......................... 92
             6.6.6.  Hard Address.................................... 92
             6.6.7.  Port IP Address................................. 92
             6.6.8.  Class of Service (COS).......................... 93
             6.6.9.  FC-4 Types...................................... 93
             6.6.10. FC-4 Descriptor................................. 93
             6.6.11. FC-4 Features .................................. 93
             6.6.12. iFCP SCN Bitmap................................. 93
             6.6.13. Port Role....................................... 94
             6.6.14. Permanent Port Name (PPN)....................... 95
       6.7.  Node-Keyed Attributes .................................. 95
             6.7.1.  FC Node Name (WWNN)............................. 95
             6.7.2.  Symbolic Node Name.............................. 95



Tseng, et al.              Standards Track                      [Page 4]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


             6.7.3.  Node IP Address................................. 95
             6.7.4.  Node IPA........................................ 96
             6.7.5.  Proxy iSCSI Name................................ 96
       6.8.  Other Attributes........................................ 96
             6.8.1.  FC-4 Type Code.................................. 96
             6.8.2.  iFCP Switch Name................................ 96
             6.8.3.  iFCP Transparent Mode Commands.................. 97
       6.9.  iSNS Server-Specific Attributes......................... 97
             6.9.1.  iSNS Server Vendor OUI.......................... 98
       6.10. Vendor-Specific Attributes.............................. 98
             6.10.1. Vendor-Specific Server Attributes............... 98
             6.10.2. Vendor-Specific Entity Attributes............... 98
             6.10.3. Vendor-Specific Portal Attributes............... 99
             6.10.4. Vendor-Specific iSCSI Node Attributes........... 99
             6.10.5. Vendor-Specific FC Port Name Attributes......... 99
             6.10.6. Vendor-Specific FC Node Name Attributes......... 99
             6.10.7. Vendor-Specific Discovery Domain Attributes..... 99
             6.10.8. Vendor-Specific Discovery Domain Set Attributes. 99
             6.10.9. Other Vendor-Specific Attributes................ 99
       6.11. Discovery Domain Registration Attributes............... 100
             6.11.1. DD Set ID Keyed Attributes..................... 100
             6.11.2. DD ID Keyed Attributes......................... 101
   7.  Security Considerations...................................... 103
       7.1.  iSNS Security Threat Analysis ......................... 103
       7.2.  iSNS Security Implementation and Usage Requirements.... 104
       7.3.  Discovering Security Requirements of Peer Devices...... 105
       7.4.  Configuring Security Policies of iFCP/iSCSI Devices.... 106
       7.5.  Resource Issues........................................ 107
       7.6.  iSNS Interaction with IKE and IPSec.................... 107
   8.  IANA Considerations.......................................... 107
       8.1.  Registry of Block Storage Protocols.................... 107
       8.2.  Registry of Standard iSNS Attributes .................. 108
       8.3.  Block Structure Descriptor (BSD) Registry.............. 108
   9.  Normative References......................................... 109
   10. Informative References....................................... 110
   Appendix A: iSNS Examples........................................ 112
       A.1.  iSCSI Initialization Example........................... 112
             A.1.1.  Simple iSCSI Target Registration............... 112
             A.1.2.  Target Registration and DD Configuration....... 114
             A.1.3.  Initiator Registration and Target Discovery.... 117
   Acknowledgements................................................. 121










Tseng, et al.              Standards Track                      [Page 5]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


1.  Introduction

1.1.  Conventions Used in This Document

   "iSNS" refers to the storage network model and associated services
   covered in the text of this document.

   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 [RFC2119].

   All frame formats are in big endian network byte order.

   All unused fields and bitmaps, including those that are RESERVED,
   SHOULD be set to zero when sending and ignored when receiving.

1.2.  Purpose of This Document

   This is a standards track document containing normative text
   specifying the iSNS Protocol, used by iSCSI and iFCP devices to
   communicate with the iSNS server.  This document focuses on the
   interaction between iSNS servers and iSNS clients; interactions among
   multiple authoritative primary iSNS servers are a potential topic for
   future work.

2.  iSNS Overview

   iSNS facilitates scalable configuration and management of iSCSI and
   Fibre Channel (FCP) storage devices in an IP network by providing a
   set of services comparable to that available in Fibre Channel
   networks.  iSNS thus allows a commodity IP network to function at a
   level of intelligence comparable to a Fibre Channel fabric.  iSNS
   allows the administrator to go beyond a simple device-by-device
   management model, where each storage device is manually and
   individually configured with its own list of known initiators and
   targets.  Using the iSNS, each storage device subordinates its
   discovery and management responsibilities to the iSNS server.  The
   iSNS server thereby serves as the consolidated configuration point
   through which management stations can configure and manage the entire
   storage network, including both iSCSI and Fibre Channel devices.

   iSNS can be implemented to support iSCSI and/or iFCP protocols as
   needed; an iSNS implementation MAY provide support for one or both of
   these protocols as desired by the implementor.  Implementation
   requirements within each of these protocols are further discussed in
   Section 5.  Use of iSNS is OPTIONAL for iSCSI and REQUIRED for iFCP.





Tseng, et al.              Standards Track                      [Page 6]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


2.1.  iSNS Architectural Components

2.1.1.  iSNS Protocol (iSNSP)

   The iSNS Protocol (iSNSP) is a flexible and lightweight protocol that
   specifies how iSNS clients and servers communicate.  It is suitable
   for various platforms, including switches and targets as well as
   server hosts.

2.1.2.  iSNS Client

   iSNS clients initiate transactions with iSNS servers using the iSNSP.
   iSNS clients are processes that are co-resident in the storage
   device, and that can register device attribute information, download
   information about other registered clients in a common Discovery
   Domain (DD), and receive asynchronous notification of events that
   occur in their DD(s).  Management stations are a special type of iSNS
   client that have access to all DDs stored in the iSNS.

2.1.3.  iSNS Server

   iSNS servers respond to iSNS protocol queries and requests, and
   initiate iSNS protocol State Change Notifications.  Properly
   authenticated information submitted by a registration request is
   stored in an iSNS database.

2.1.4.  iSNS Database

   The iSNS database is the information repository for the iSNS
   server(s).  It maintains information about iSNS client attributes.  A
   directory-enabled implementation of iSNS may store client attributes
   in an LDAP directory infrastructure.

2.1.5.  iSCSI

   iSCSI (Internet SCSI) is an encapsulation of SCSI for a new
   generation of storage devices interconnected with TCP/IP [iSCSI].

2.1.6.  iFCP

   iFCP (Internet FCP) is a gateway-to-gateway protocol designed to
   interconnect existing Fibre Channel and SCSI devices using TCP/IP.
   iFCP maps the existing FCP standard and associated Fibre Channel
   services to TCP/IP [iFCP].







Tseng, et al.              Standards Track                      [Page 7]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


2.2.  iSNS Functional Overview

   There are four main functions of the iSNS:

   1)  A Name Service Providing Storage Resource Discovery

   2)  Discovery Domain (DD) and Login Control Service

   3)  State Change Notification Service

   4)  Open Mapping of Fibre Channel and iSCSI Devices

2.2.1.  Name Registration Service

   The iSNS provides a registration function to allow all entities in a
   storage network to register and query the iSNS database.  Both
   targets and initiators can register in the iSNS database, as well as
   query for information about other initiators and targets.  This
   allows, for example, a client initiator to obtain information about
   target devices from the iSNS server.  This service is modeled on the
   Fibre Channel Generic Services Name Server described in FC-GS-4, with
   extensions, operating within the context of an IP network.

   The naming registration service also provides the ability to obtain a
   network-unique Domain ID for iFCP gateways when one is required.

2.2.2.  Discovery Domain and Login Control Service

   The Discovery Domain (DD) Service facilitates the partitioning of
   Storage Nodes into more manageable groupings for administrative and
   login control purposes.  It allows the administrator to limit the
   login process of each host to the more appropriate subset of targets
   registered in the iSNS.  This is particularly important for reducing
   the number of unnecessary logins (iSCSI logins or Fibre Channel Port
   Logins), and for limiting the amount of time that the host spends
   initializing login relationships as the size of the storage network
   scales up.  Storage Nodes must be in at least one common enabled DD
   in order to obtain information about each other.  Devices can be
   members of multiple DDs simultaneously.

   Login Control allows targets to delegate their access
   control/authorization policies to the iSNS server.  This is
   consistent with the goal of centralizing management of those storage
   devices using the iSNS server.  The target node or device downloads
   the list of authorized initiators from the iSNS.  Each node or device
   is uniquely identified by an iSCSI Name or FC Port Name.  Only





Tseng, et al.              Standards Track                      [Page 8]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   initiators that match the required identification and authorization
   provided by the iSNS will be allowed access by that target Node
   during session establishment.

   Placing Portals of a Network Entity into Discovery Domains allows
   administrators to indicate the preferred IP Portal interface through
   which storage traffic should access specific Storage Nodes of that
   Network Entity.  If no Portals of a Network Entity have been placed
   into a DD, then queries scoped to that DD SHALL report all Portals of
   that Network Entity.  If one or more Portals of a Network Entity have
   been placed into a DD, then queries scoped to that DD SHALL report
   only those Portals that have been explicitly placed in the DD.

   DDs can be managed offline through a separate management workstation
   using the iSNSP or SNMP.  If the target opts to use the Login Control
   feature of the iSNS, the target delegates management of access
   control policy (i.e., the list of initiators allowed to log in to
   that target) to the management workstations that are managing the
   configuration in the iSNS database.

   If administratively authorized, a target can upload its own Login
   Control list.  This is accomplished using the DDReg message and
   listing the iSCSI name of each initiator to be registered in the
   target's DD.

   An implementation MAY decide that newly registered devices that have
   not explicitly been placed into a DD by the management station will
   be placed into a "default DD" contained in a "default DDS" whose
   initial DD Set Status value is "enabled".  This makes them visible to
   other devices in the default DD.  Other implementations MAY decide
   that they are registered with no DD, making them inaccessible to
   source-scoped iSNSP messages.

   The iSNS server uses the Source Attribute of each iSNSP message to
   determine the originator of the request and to scope the operation to
   a set of Discovery Domains.  In addition, the Node Type (specified in
   the iFCP or iSCSI Node Type bitmap field) may also be used to
   determine authorization for the specified iSNS operation.  For
   example, only Control Nodes are authorized to create or delete
   discovery domains.

   Valid and active Discovery Domains (DDs) belong to at least one
   active Discovery Domain Set (DDS).  Discovery Domains that do not
   belong to an activated DDS are not enabled.  The iSNS server MUST
   maintain the state of DD membership for all Storage Nodes, even for
   those that have been deregistered.  DD membership is persistent
   regardless of whether a Storage Node is actively registered in the
   iSNS database.



Tseng, et al.              Standards Track                      [Page 9]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


2.2.3.  State Change Notification Service

   The State Change Notification (SCN) service allows the iSNS Server to
   issue notifications about network events that affect the operational
   state of Storage Nodes.  The iSNS client may register for
   notifications on behalf of its Storage Nodes for notification of
   events detected by the iSNS Server.  SCNs notify iSNS clients of
   explicit or implicit changes to the iSNS database; they do not
   necessarily indicate the state of connectivity to peer storage
   devices in the network.  The response of a storage device to receipt
   of an SCN is implementation-specific; the policy for responding to
   SCNs is outside of the scope of this document.

   There are two types of SCN registrations: regular registrations and
   management registrations.  Management registrations result in
   management SCNs, whereas regular registrations result in regular
   SCNs.  The type of registration and SCN message is indicated in the
   SCN bitmap (see Sections 6.4.4 and 6.6.12).

   A regular SCN registration indicates that the Discovery Domain
   Service SHALL be used to control the distribution of SCN messages.
   Receipt of regular SCNs is limited to the discovery domains in which
   the SCN-triggering event takes place.  Regular SCNs do not contain
   information about discovery domains.

   A management SCN registration can only by requested by Control Nodes.
   Management SCNs resulting from management registrations are not bound
   by the Discovery Domain service.  Authorization to request management
   SCN registrations may be administratively controlled.

   The iSNS server SHOULD be implemented with hardware and software
   resources sufficient to support the expected number of iSNS clients.
   However, if resources are unexpectedly exhausted, then the iSNS
   server MAY refuse SCN service by returning an SCN Registration
   Rejected (Status Code 17).  The rejection might occur in situations
   where the network size or current number of SCN registrations has
   passed an implementation-specific threshold.  A client not allowed to
   register for SCNs may decide to monitor its sessions with other
   storage devices directly.


   The specific notification mechanism by which the iSNS server learns
   of the events that trigger SCNs is implementation-specific, but can
   include examples such as explicit notification messages from an iSNS
   client to the iSNS server, or a hardware interrupt to a switch-hosted
   iSNS server as a result of link failure.





Tseng, et al.              Standards Track                     [Page 10]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


2.2.4.  Open Mapping between Fibre Channel and iSCSI Devices

   The iSNS database stores naming and discovery information about both
   Fibre Channel and iSCSI devices.  This allows the iSNS server to
   store mappings of a Fibre Channel device to a proxy iSCSI device
   "image" in the IP network.  Similarly, mappings of an iSCSI device to
   a "proxy WWN" can be stored under the WWNN Token field for that iSCSI
   device.

   Furthermore, through use of iSCSI-FC gateways, Fibre Channel-aware
   management stations can interact with the iSNS server to retrieve
   information about Fibre Channel devices, and use this information to
   manage Fibre Channel and iSCSI devices.  This allows management
   functions such as Discovery Domains and State Change Notifications to
   be applied seamlessly to both iSCSI and Fibre Channel devices,
   facilitating integration of IP networks with Fibre Channel devices
   and fabrics.

   Note that Fibre Channel attributes are stored as iFCP attributes, and
   that the ability to store this information in the iSNS server is
   useful even if the iFCP protocol is not implemented.  In particular,
   tag 101 can be used to store a "Proxy iSCSI Name" for Fibre Channel
   devices registered in the iSNS server.  This field is used to
   associate the FC device with an iSCSI registration entry that is used
   for the Fibre Channel device to communicate with iSCSI devices in the
   IP network.  Conversely, tag 37 (see Section 6.1) contains a WWNN
   Token field, which can be used to store an FC Node Name (WWNN) value
   used by iSCSI-FC gateways to represent an iSCSI device in the Fibre
   Channel domain.

   By storing the mapping between Fibre Channel and iSCSI devices in the
   iSNS server, this information becomes open to any authorized iSNS
   client wishing to retrieve and use this information.  In many cases,
   this provides advantages over storing the information internally
   within an iSCSI-FC gateway, where the mapping is inaccessible to
   other devices except by proprietary mechanisms.

2.3.  iSNS Usage Model

   The following is a high-level description of how each type of device
   in a storage network can utilize iSNS.  Each type of device interacts
   with the iSNS server as an iSNS client and must register itself in
   the iSNS database in order to access services provided by the iSNS.








Tseng, et al.              Standards Track                     [Page 11]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


2.3.1.  iSCSI Initiator

   An iSCSI initiator will query the iSNS server to discover the
   presence and location of iSCSI target devices.  It may also request
   state change notifications (SCNs) so that it can be notified of new
   targets that appear on the network after the initial bootup and
   discovery.  SCNs can also inform the iSCSI initiator of targets that
   have been removed from or no longer available in the storage network,
   so that incomplete storage sessions can be gracefully terminated and
   resources for non-existent targets can be reallocated.

2.3.2.  iSCSI Target

   An iSCSI target allows itself to be discovered by iSCSI initiators by
   registering its presence in the iSNS server.  It may also register
   for SCNs in order to detect the addition or removal of initiators for
   resource allocation purposes.  The iSCSI target device may also
   register for Entity Status Inquiry (ESI) messages, which allow the
   iSNS to monitor the target device's availability in the storage
   network.

2.3.3.  iSCSI-FC Gateway

   An iSCSI-FC gateway bridges devices in a Fibre Channel network to an
   iSCSI/IP network.  It may use the iSNS server to store FC device
   attributes discovered in the FC name server, as well as mappings of
   FC device identifiers to iSCSI device identifiers.  iSNS has the
   capability to store all attributes of both iSCSI and Fibre Channel
   devices; iSCSI devices are managed through direct interaction using
   iSNS, while FC devices can be indirectly managed through iSNS
   interactions with the iSCSI-FC gateway.  This allows both iSCSI and
   Fibre Channel devices to be managed in a seamless management
   framework.

2.3.4.  iFCP Gateway

   An iFCP gateway uses iSNS to emulate the services provided by a Fibre
   Channel name server for FC devices in its gateway region.  iSNS
   provides basic discovery and zoning configuration information to be
   enforced by the iFCP gateway.  When queried, iSNS returns information
   on the N_Port network address used to establish iFCP sessions between
   FC devices supported by iFCP gateways.

2.3.5.  Management Station

   A management station uses iSNS to monitor storage devices and to
   enable or disable storage sessions by configuring discovery domains.
   A management station usually interacts with the iSNS server as a



Tseng, et al.              Standards Track                     [Page 12]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   Control Node endowed with access to all iSNS database records and
   with special privileges to configure discovery domains.  Through
   manipulation of discovery domains, the management station controls
   the scope of device discovery for iSNS clients querying the iSNS
   server.

2.4.  Administratively Controlled iSNS Settings

   Some important operational settings for the iSNS server are
   configured using administrative means, such as a configuration file,
   a console port, an SNMP, or another implementation-specific method.
   These administratively-controlled settings cannot be configured using
   the iSNS Protocol, and therefore the iSNS server implementation MUST
   provide for such an administrative control interface.

   The following is a list of parameters that are administratively
   controlled for the iSNS server.  In the absence of alternative
   settings provided by the administrator, the following specified
   default settings MUST be used.

   Setting                                  Default Setting
   -------                                  ---------------
   ESI Non-Response Threshold                     3     (see 5.6.5.13)
   Management SCNs (Control Nodes only)        enabled  (see 5.6.5.8)
   Default DD/DDS                              disabled
   DD/DDS Modification
      - Control Node                           enabled
      - iSCSI Target Node Type                 disabled
      - iSCSI Initiator Node Type              disabled
      - iFCP Target Port Role                  disabled
      - iFCP Initiator Port Role               disabled
   Authorized Control Nodes                      N/A

   ESI Non-Response Threshold: determines the number of ESI messages
                   sent without receiving a response before the network
                   entity is deregistered from the iSNS database.

   Management SCN for Control Node: determines whether a registered
                   Control Node is permitted to register to receive
                   Management SCNs.

   Default DD/DDS: determines whether a newly registered device not
                   explicitly placed into a discovery domain (DD) and
                   discovery domain set (DDS) is placed into a default
                   DD/DDS.

   DD/DDS Modification: determines whether the specified type of Node is
                   allowed to add, delete or update DDs and DDSs.



Tseng, et al.              Standards Track                     [Page 13]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   Authorized Control Nodes: a list of Nodes identified by iSCSI Name or
                   FC Port Name WWPN that are authorized to register as
                   Control Nodes.

2.5.  iSNS Server Discovery

2.5.1.  Service Location Protocol (SLP)

   The Service Location Protocol (SLP) provides a flexible and scalable
   framework for providing hosts with access to information about the
   existence, location, and configuration of networked services,
   including the iSNS server.  SLP can be used by iSNS clients to
   discover the IP address or FQDN of the iSNS server.  To implement
   discovery through SLP, a Service Agent (SA) should be cohosted in the
   iSNS server, and a User Agent (UA) should be in each iSNS client.
   Each client multicasts a discovery message requesting the IP address
   of the iSNS server(s).  The SA responds to this request.  Optionally,
   the location of the iSNS server can be stored in the SLP Directory
   Agent (DA).

   Note that a complete description and specification of SLP can be
   found in [RFC2608], and is beyond the scope of this document.  A
   service template for using SLP to locate iSNS servers can be found in
   [iSCSI-SLP].

2.5.2.  Dynamic Host Configuration Protocol (DHCP)

   The IP address of the iSNS server can be stored in a DHCP server to
   be downloaded by iSNS clients using a DHCP option.  The DHCP option
   number to be used for distributing the iSNS server location is found
   in [iSNSOption].

2.5.3.  iSNS Heartbeat Message

   The iSNS heartbeat message is described in Section 5.6.5.14.  It
   allows iSNS clients within the broadcast or multicast domain of the
   iSNS server to discover the location of the active iSNS server and
   any backup servers.

2.6.  iSNS and Network Address Translation (NAT)

   The existence of NAT will have an impact upon information retrieved
   from the iSNS server.  If the iSNS client exists in an addressing
   domain different from that of the iSNS server, then IP address
   information stored in the iSNS server may not be correct when
   interpreted in the domain of the iSNS client.





Tseng, et al.              Standards Track                     [Page 14]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   There are several possible approaches to allow operation of iSNS
   within a NAT network.  The first approach is to require use of the
   canonical TCP port number by both targets and initiators when
   addressing targets across a NAT boundary, and for the iSNS client not
   to query for nominal IP addresses.  Rather, the iSNS client queries
   for the DNS Fully Qualified Domain Name stored in the Entity
   Identifier field when seeking addressing information.  Once
   retrieved, the DNS name can be interpreted in each address domain and
   mapped to the appropriate IP address by local DNS servers.

   A second approach is to deploy a distributed network of iSNS servers.
   Local iSNS servers are deployed inside and outside NAT boundaries,
   with each local server storing relevant IP addresses for their
   respective NAT domains.  Updates among the network of decentralized,
   local iSNS servers are handled using LDAP and appropriate NAT
   translation rules implemented within the update mechanism in each
   server.

   Finally, note that it is possible for an iSNS server in the private
   addressing domain behind a NAT boundary to exclusively support iSNS
   clients that are operating in the global IP addressing domain.  If
   this is the case, the administrator only needs to ensure that the
   appropriate mappings are configured on the NAT gateways to allow the
   iSNS clients to initiate iSNSP sessions to the iSNS server.  All
   registered addresses contained in the iSNS server are thus public IP
   addresses for use outside the NAT boundary.  Care should be taken to
   ensure that there are no iSNS clients querying the server from inside
   the NAT boundary.

2.7.  Transfer of iSNS Database Records between iSNS Servers

   Transfer of iSNS database records between iSNS servers has important
   applications, including the following:

   1)  An independent organization needs to transfer storage information
       to a different organization.  Each organization independently
       maintains its own iSNS infrastructure.  To facilitate discovery
       of storage assets of the peer organization using IP, iSNS
       database records can be transferred between authoritative iSNS
       servers from each organization.  This allows storage sessions to
       be established directly between devices residing in each
       organization's storage network infrastructure over a common IP
       network.

   2)  Multiple iSNS servers are desired for redundancy.  Backup servers
       need to maintain copies of the primary server's dynamically
       changing database.




Tseng, et al.              Standards Track                     [Page 15]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   To support the above applications, information in an iSNS server can
   be distributed to other iSNS servers either using the iSNS protocol,
   or through out-of-band mechanisms using non-iSNS protocols.  The
   following examples illustrate possible methods for transferring data
   records between iSNS servers.  In the first example, a back-end LDAP
   information base is used to support the iSNS server, and the data is
   transferred using the LDAP protocol.  Once the record transfer of the
   remote device is completed, it becomes visible and accessible to
   local devices using the local iSNS server.  This allows local devices
   to establish sessions with remote devices (provided that firewall
   boundaries can be negotiated).

   +-------------------------+           +-------------------------+
   |+------+ iSNSP           |           |           iSNSP +-----+ |
   ||dev A |<----->+------+  |           |  +------+<----->|dev C| |
   |+------+       |      |  |           |  |      |       +-----+ |
   |+------+ iSNSP |local |  |           |  |remote| iSNSP +-----+ |
   ||dev B |<----->| iSNS |  |           |  | iSNS |<----->|dev D| |
   |+------+       |server|  |           |  |server|       +-----+ |
   |........       +--+---+  |   WAN     |  +---+--+               |
   |.dev C'.          |      |   Link    |      |                  |
   |........          |      =============      |                  |
   |                  |      |           |      |                  |
   |               +--+---+  |           |  +---+--+               |
   |               | local|<--- <--- <--- <-|remote|               |
   |               | LDAP |  |  LDAP:    |  | LDAP |               |
   |               +------+  Xfer "dev C"|  +------+               |
   +-------------------------+           +-------------------------+
          Enterprise                           Enterprise
          Network A                            Network B

   In the above diagram, two business partners wish to share storage
   "dev C".  Using LDAP, the record for "dev C" can be transferred from
   Network B to Network A.  Once accessible to the local iSNS server in
   Network A, local devices A and B can now discover and connect to "dev
   C".















Tseng, et al.              Standards Track                     [Page 16]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   +-------------------------+           +-------------------------+
   |+------+ iSNSP           |           |           iSNSP +-----+ |
   ||dev A |<----->+------+  |           |  +------+<----->|dev C| |
   |+------+       |      |  |           |  |      |       +-----+ |
   |+------+ iSNSP |local |  |           |  |remote| iSNSP +-----+ |
   ||dev B |<----->| iSNS |  |           |  | iSNS |<----->|dev D| |
   |+------+       |server|  |           |  |server|       +-----+ |
   |........       +------+  |   WAN     |  +---+--+               |
   |.dev C'.          ^      |   Link    |      |                  |
   |........          |      =============      v                  |
   |                  |      |           |      |SNMP              |
   |                  |      |           |      |                  |
   |               +--+----+ |           |      v                  |
   |               | SNMP  |<--- <--- <--- <----                   |
   |               | Mgmt  | |  SNMP: Xfer "dev C"                 |
   |               |Station| |           |                         |
   |               +-------+ |           |                         |
   +-------------------------+           +-------------------------+
          Enterprise                           Enterprise
          Network A                            Network B

   The above diagram illustrates a second example of how iSNS records
   can be shared.  This method uses an SNMP-based management station to
   retrieve (GET) the desired record for "dev C" manually, and then to
   store (SET) it on the local iSNS server directly.  Once the record is
   transferred to the local iSNS server in Network A, "dev C" becomes
   visible and accessible (provided that firewall boundaries can be
   negotiated) to other devices in Network A.

   Other methods, including proprietary protocols, can be used to
   transfer device records between iSNS servers.  Further discussion and
   explanation of these methodologies is beyond the scope of this
   document.

2.8.  Backup iSNS Servers

   This section offers a broad framework for implementation and
   deployment of iSNS backup servers.  Server failover and recovery are
   topics of continuing research, and adequate resolution of issues such
   as split brain and primary server selection is dependent on the
   specific implementation requirements and deployment needs.  The
   failover mechanisms discussed in this document focus on the
   interaction between iSNS clients and iSNS servers.  Specifically,
   what is covered in this document includes the following:

   -  iSNS client behavior and the iSNS protocol interaction between the
      client and multiple iSNS servers, some of which are backup
      servers.



Tseng, et al.              Standards Track                     [Page 17]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   -  Required failover behaviors of the collection of iSNS servers that
      includes active and backup servers.

   However, note that this document does not specify the complete
   functional failover requirements of each iSNS server.  In particular,
   it does not specify the complete set of protocol interactions among
   the iSNS servers that are required to achieve stable failover
   operation in an interoperable manner.

   For the purposes of this discussion, the specified backup mechanisms
   pertain to interaction among different logical iSNS servers.  Note
   that it is possible to create multiple physical iSNS servers to form
   a single logical iSNS server cluster, and thus to distribute iSNS
   transaction processing among multiple physical servers.  However, a
   more detailed discussion of the interactions between physical servers
   within a logical iSNS server cluster is beyond the scope of this
   document.

   Multiple logical iSNS servers can be used to provide redundancy in
   the event that the active iSNS server fails or is removed from the
   network.  The methods described in Section 2.7 above can be used to
   transfer name server records to backup iSNS servers.  Each backup
   server maintains a redundant copy of the name server database found
   in the primary iSNS server, and can respond to iSNS protocol messages
   in the same way as the active server.  Each backup server SHOULD
   monitor the health and status of the active iSNS server, including
   checking to make sure its own database is synchronized with the
   active server's database.  How each backup server accomplishes this
   is implementation-dependent, and may (or may not) include using the
   iSNS protocol.  If the iSNS protocol is used, then the backup server
   MAY register itself in the active server's iSNS database as a Control
   Node, allowing it to receive state-change notifications.

   Generally, the administrator or some automated election process is
   responsible for initial and subsequent designation of the primary
   server and each backup server.

   A maximum of one logical backup iSNS server SHALL exist at any
   individual IP address, in order to avoid conflicts from multiple
   servers listening on the same canonical iSNS TCP or UDP port number.

   The iSNS heartbeat can also be used to coordinate the designation and
   selection of primary and backup iSNS servers.

   Each backup server MUST note its relative precedence in the active
   server's list of backup servers.  If its precedence is not already
   known, each backup server MAY learn it from the iSNS heartbeat
   message, by noting the position of its IP address in the ordered list



Tseng, et al.              Standards Track                     [Page 18]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   of backup server IP addresses.  For example, if it is the first
   backup listed in the heartbeat message, then its backup precedence is
   1.  If it is the third backup server listed, then its backup
   precedence is 3.

   If a backup server establishes that it has lost connectivity to the
   active server and other backup servers of higher precedence, then it
   SHOULD assume that it is the active server.  The method of
   determining whether connectivity has been lost is implementation-
   specific.  One possible approach is to assume that if the backup
   server does not receive iSNS heartbeat messages for a period of time,
   then connectivity to the active server has been lost.  Alternatively,
   the backup server may establish TCP connections to the active server
   and other backup servers, with loss of connectivity determined
   through non-response to periodic echo or polling messages (using
   iSNSP, SNMP, or other protocols).

   When a backup server becomes the active server, it SHALL assume all
   active server responsibilities, including (if used) transmission of
   the iSNS heartbeat message.  If transmitting the iSNS heartbeat, the
   backup server replaces the active Server IP Address and TCP/UDP Port
   entries with its own IP address and TCP/UDP Port, and begins
   incrementing the counter field from the last known value from the
   previously-active iSNS server.  However, it MUST NOT change the
   original ordered list of backup server IP Address and TCP/UDP Port
   entries.  If the primary backup server or other higher-precedence
   backup server returns, then the existing active server is responsible
   for ensuring that the new active server's database is up-to-date
   before demoting itself to its original status as backup.

   Since the primary and backup iSNS servers maintain a coordinated
   database, no re-registration by an iSNS Client is required when a
   backup server takes the active server role.  Likewise, no re-
   registration by an iSNS Client is required when the previous primary
   server returns to the active server role.

2.9.  Transport Protocols

   The iSNS Protocol is transport-neutral.  Query and registration
   messages are transported over TCP or UDP.  iSNS heartbeat messages
   are transported using IP multicast or broadcast.

2.9.1.  Use of TCP for iSNS Communication

   It MUST be possible to use TCP for iSNS communication.  The iSNS
   server MUST accept TCP connections for client registrations.  To
   receive Entity Status Inquiry (ESI) (see Section 5.6.5.13) monitoring
   the use of TCP, the client registers the Portal ESI Interval and the



Tseng, et al.              Standards Track                     [Page 19]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   port number of the TCP port that will be used to receive ESI
   messages.  The iSNS server initiates the TCP connection used to
   deliver the ESI message.  This TCP connection does not need to be
   continuously open.

   To receive SCN notifications using TCP, the client registers the
   iSCSI or iFCP SCN Bitmap and the port number of the TCP port in the
   Portal used to receive SCNs.  The iSNS server initiates the TCP
   connection used to deliver the SCN message.  This TCP connection does
   not need to be continuously open.

   It is possible for an iSNS client to use the same TCP connection for
   SCN, ESI, and iSNS queries.  Alternatively, separate connections may
   be used.

2.9.2.  Use of UDP for iSNS Communication

   The iSNS server MAY accept UDP messages for client registrations.
   The iSNS server MUST accept registrations from clients requesting
   UDP-based ESI and SCN messages.

   To receive UDP-based ESI monitoring messages, the client registers
   the port number of the UDP port in at least one Portal to be used to
   receive and respond to ESI messages from the iSNS server.  If a
   Network Entity has multiple Portals with registered ESI UDP Ports,
   then ESI messages SHALL be delivered to every Portal registered to
   receive such messages.

   To receive UDP-based SCN notification messages, the client registers
   the port number of the UDP port in at least one Portal to be used to
   receive SCN messages from the iSNS server.  If a Network Entity has
   multiple Portals with registered SCN UDP Ports, then SCN messages
   SHALL be delivered to each Portal registered to receive such
   messages.

   When using UDP to transport iSNS messages, each UDP datagram MUST
   contain exactly one iSNS PDU (see Section 5).

2.9.3.  iSNS Multicast and Broadcast Messages

   iSNS multicast messages are transported using IP multicast or
   broadcast.  The iSNS heartbeat is the only iSNS multicast or
   broadcast message.  This message is originated by the iSNS server and
   sent to all iSNS clients that are listening on the IP multicast
   address allocated for the iSNS heartbeat.






Tseng, et al.              Standards Track                     [Page 20]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


2.10.  Simple Network Management Protocol (SNMP) Requirements

   The iSNS Server may be managed via the iSNS MIB [iSNSMIB] using an
   SNMP management framework [RFC3411].  For a detailed overview of the
   documents that describe the current Internet-Standard Management
   Framework, please refer to Section 7 of RFC 3410 [RFC3410].  The iSNS
   MIB provides the ability to configure and monitor an iSNS server
   without using the iSNS protocol directly.  SNMP management frameworks
   have several requirements for object indexing in order for objects to
   be accessed or added.

   SNMP uses an Object Identifier (OID) for object identification.  The
   size of each OID is restricted to a maximum of 128 sub-identifiers.
   Both the iSCSI and iFCP protocol contain identifiers, such as the
   iSCSI Name, that are greater the 128 characters in length.  Using
   such identifiers as an index would result in more than 128 sub-
   identifiers per OID.  In order to support objects that have key
   identifiers whose maximum length is longer than the maximum SNMP-
   supported length, the iSNS server provides secondary non-zero integer
   index identifiers.  These indexes SHALL be persistent for as long as
   the server is active.  Furthermore, index values for recently
   deregistered objects SHOULD NOT be reused in the short term.  Object
   attributes, including indexes, are described in detail in Section 6.

   For SNMP based management applications to create a new entry in a
   table of objects, a valid OID must be available to specify the table
   row.  The iSNS server supports this by providing, for each type of
   object that can be added via SNMP, an object attribute that returns
   the next available non-zero integer index.  This allows an SNMP
   client to request an OID to be used for registering a new object in
   the server.  Object attributes, including next available index
   attributes, are described in detail in Section 6.

3.  iSNS Object Model

   iSNS provides the framework for the registration, discovery, and
   management of iSCSI devices and Fibre Channel-based devices (using
   iFCP).  This architecture framework provides elements needed to
   describe various storage device objects and attributes that may exist
   on an IP storage network.  Objects defined in this architecture
   framework include Network Entity, Portal, Storage Node, FC Device,
   Discovery Domain, and Discovery Domain Set.  Each of these objects is
   described in greater detail in the following sections.








Tseng, et al.              Standards Track                     [Page 21]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


3.1.  Network Entity Object

   The Network Entity object is a container of Storage Node objects and
   Portal objects.  It represents the infrastructure supporting access
   to a unique set of one or more Storage Nodes.  The Entity Identifier
   attribute uniquely distinguishes a Network Entity, and is the key
   used to register a Network Entity object in an iSNS server.  All
   Storage Nodes and Portals contained within a single Network Entity
   object operate as a cohesive unit.

   Note that it is possible for a single physical device or gateway to
   be represented by more than one logical Network Entity in the iSNS
   database.  For example, one of the Storage Nodes on a physical device
   may be accessible from only a subset of the network interfaces (i.e.,
   Portals) available on that device.  In this case, a logical network
   entity (i.e., a "shadow entity") is created and used to contain the
   Portals and Storage Nodes that can operate cooperatively.  No object
   (Portals, Storage Nodes, etc.) can be contained in more than one
   logical Network Entity.

   Similarly, it is possible for a logical Network Entity to be
   supported by more than one physical device or gateway.  For example,
   multiple FC-iSCSI gateways may be used to bridge FC devices in a
   single Fibre Channel network.  Collectively, the multiple gateways
   can be used to support a single logical Network Entity that is used
   to contain all the devices in that Fibre Channel network.

3.2.  Portal Object

   The Portal object is an interface through which access to Storage
   Nodes within the Network Entity can be obtained.  The IP address and
   TCP/UDP Port number attributes uniquely distinguish a Portal object,
   and combined are the key used to register a Portal object in an iSNS
   server.  A Portal is contained in one and only one Network Entity,
   and may be contained in one or more DDs (see Section 3.6).

3.3.  Storage Node Object

   The Storage Node object is the logical endpoint of an iSCSI or iFCP
   session.  In iFCP, the session endpoint is represented by the World
   Wide Port Name (WWPN).  In iSCSI, the session endpoint is represented
   by the iSCSI Name of the device.  For iSCSI, the iSCSI Name attribute
   uniquely distinguishes a Storage Node, and is the key used to
   register a Storage Node object in an iSNS Server.  For iFCP, the FC
   Port Name (WWPN) attribute uniquely distinguishes a Storage Node, and
   is the key used to register a Storage Node object in the iSNS Server.
   Storage Node is contained in only one Network Entity object and may
   be contained in one or more DDs (see Section 3.6).



Tseng, et al.              Standards Track                     [Page 22]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


3.4.  Portal Group Object

   The Portal Group (PG) object represents an association between a
   Portal and an iSCSI Node.  Each Portal and iSCSI Storage Node
   registered in an Entity can be associated using a Portal Group (PG)
   object.  The PG Tag (PGT), if non-NULL, indicates that the associated
   Portal provides access to the associated iSCSI Storage Node in the
   Entity.  All Portals that have the same PGT value for a specific
   iSCSI Storage Node allow coordinated access to that node.

   A PG object MAY be registered when a Portal or iSCSI Storage Node is
   registered.  Each Portal to iSCSI Node association is represented by
   one and only one PG object.  In order for a Portal to provide access
   to an iSCSI Node, the PGT of the PG object MUST be non-NULL.  If the
   PGT value registered for a specified Portal and iSCSI Node is NULL,
   or if no PGT value is registered, then the Portal does not provide
   access to that iSCSI Node in the Entity.

   The PGT value indicates whether access to an iSCSI Node can be
   coordinated across multiple Portals.  All Portals that have the same
   PGT value for a specific iSCSI Node can provide coordinated access to
   that iSCSI Node.  According to the iSCSI Specification, coordinated
   access to an iSCSI node indicates the capability of coordinating an
   iSCSI session with connections that span these Portals [iSCSI].

   The PG object is uniquely distinguished by the iSCSI Name, Portal IP
   Address, and Portal TCP Port values of the associated Storage Node
   and Portal objects.  These are represented in the iSNS Server by the
   PG iSCSI Name, PG Portal IP Address, and PG Portal TCP/UDP Port
   attributes, respectively.  The PG object is also uniquely
   distinguished in the iSNS Server by the PG Index value.

   A new PG object can only be registered by referencing its associated
   iSCSI Storage Node or Portal object.  A pre-existing PG object can be
   modified or queried by using its Portal Group Index as message key,
   or by referencing its associated iSCSI Storage Node or Portal object.
   A 0-length Tag, Length, Value TLV is used to register a PGT NULL
   value.

   The PG object is deregistered if and only if its associated iSCSI
   Node and Portal objects are both removed.










Tseng, et al.              Standards Track                     [Page 23]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


3.5.  Device Object

   The FC Device represents the Fibre Channel Node.  This object
   contains information that may be useful in the management of the
   Fibre Channel device.  The FC Node Name (WWNN) attribute uniquely
   distinguishes an FC Device, and is the key used to register an FC
   Device object in the iSNS Server.

   The FC Device is contained in one or more Storage Node objects.

3.6.  Discovery Domain Object

   Discovery Domains (DD) are a security and management mechanism used
   to administer access and connectivity to storage devices.  For query
   and registration purposes, they are considered containers for Storage
   Node and Portal objects.  A query by an iSNS client that is not from
   a Control Node only returns information about objects with which it
   shares at least one active DD.  The only exception to this rule is
   with Portals; if Storage Nodes of a Network Entity are registered in
   the DD without Portals, then all Portals of that Network Entity are
   implicit members of that DD.  The Discovery Domain ID (DD_ID)
   attribute uniquely distinguishes a Discovery Domain object, and is
   the key used to register a Discovery Domain object in the iSNS
   Server.

   A DD is considered active if it is a member of at least one active DD
   Set.  DDs that are not members of at least one enabled DDS are
   considered disabled.  A Storage Node can be a member of one or more
   DDs.  An enabled DD establishes connectivity among the Storage Nodes
   in that DD.

3.7.  Discovery Domain Set Object

   The Discovery Domain Set (DDS) is a container object for Discovery
   Domains (DDs).  DDSs may contain one or more DDs.  Similarly, each DD
   can be a member of one or more DDSs.  DDSs are a mechanism to store
   coordinated sets of DD mappings in the iSNS server.  Active DDs are
   members of at least one active DD Set.  Multiple DDSs may be
   considered active at the same time.  The Discovery Domain Set ID
   (DDS_ID) attribute uniquely distinguishes a Discovery Domain Set
   object, and is the key used to register a Discovery Domain Set object
   in the iSNS Server.

3.8.  Database Model

   As presented to the iSNS client, each object of a specific type in
   the iSNS database MUST have an implicit internal linear ordering
   based on the key(s) for that object type.  This ordering provides the



Tseng, et al.              Standards Track                     [Page 24]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   ability to respond to DevGetNext queries (see Section 5.6.5.3).  The
   ordering of objects in the iSNS database SHOULD NOT be changed with
   respect to that implied ordering, as a consequence of object
   insertions and deletions.  That is, the relative order of surviving
   object entries in the iSNS database SHOULD be preserved so that the
   DevGetNext message encounters generally reasonable behavior.

   The following diagram shows the various objects described above and
   their relationship to each other.

                    +--------------+    +-----------+
                    |    NETWORK   |1  *|           |
                    |    ENTITY    |----|  PORTAL   |
                    |              |    |           |
                    +--------------+    +-----------+
                            |1            |1  |*
                            |             |   |
                            |             |*  |
                            |   +----------+  |
                            |   |  PORTAL  |  |
                            |   |  GROUP   |  |
                            |   +----------+  |
                            |    |*           |
                            |    |            |
                            |*   |1           |*
   +-----------+    +--------------+    +-----------+    +-----------+
   |    FC     |1  *|   STORAGE    |*  *| DISCOVERY |*  *| DISCOVERY |
   |  DEVICE   |----|    NODE      |----|  DOMAIN   |----|  DOMAIN   |
   |           |    |              |    |           |    |    SET    |
   +-----------+    +--------------+    +-----------+    +-----------+

                * represents 0 to many possible relationships

4.  iSNS Implementation Requirements

   This section details specific requirements for support of each of
   these IP storage protocols.  Implementation requirements for security
   are described in Section 7.

4.1.  iSCSI Requirements

   Use of iSNS in support of iSCSI is OPTIONAL.  iSCSI devices MAY be
   manually configured with the iSCSI Name and IP address of peer
   devices, without the aid or intervention of iSNS.  iSCSI devices may
   also use SLP [RFC2608] to discover peer iSCSI devices.  However, iSNS
   is useful for scaling a storage network to a larger number of iSCSI
   devices.




Tseng, et al.              Standards Track                     [Page 25]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


4.1.1.  Required Attributes for Support of iSCSI

   The following attributes are available to support iSCSI.  Attributes
   indicated in the REQUIRED for Server column MUST be implemented by an
   iSNS server used to support iSCSI.  Attributes indicated in the
   REQUIRED for Client column MUST be implemented by an iSCSI device
   that elects to use the iSNS.  Attributes indicated in the K (Key)
   column uniquely identify the object type in the iSNS Server.  A more
   detailed description of each attribute is found in Section 6.

                                                        REQUIRED for:
   Object             Attribute                    K    Server  Client
   ------             ---------                    -    ------  ------
   NETWORK ENTITY     Entity Identifier            *      *        *
                      Entity Protocol                     *        *
                      Management IP Address               *
                      Timestamp                           *
                      Protocol Version Range              *
                      Registration Period                 *
                      Entity Index                        *
                      Entity IKE Phase-1 Proposal
                      Entity Certificate

   PORTAL             IP Address                   *      *        *
                      TCP/UDP Port                 *      *        *
                      Portal Symbolic Name                *
                      ESI Interval                        *
                      ESI Port                            *
                      Portal Index                        *
                      SCN Port                            *
                      Portal Security Bitmap              *
                      Portal IKE Phase-1 Proposal
                      Portal IKE Phase-2 Proposal
                      Portal Certificate

   PORTAL GROUP       PG iSCSI Name                *      *        *
                      PG IP Address                *      *        *
                      PG TCP/UDP Port              *      *        *
                      PG Tag                              *        *
                      PG Index                            *











Tseng, et al.              Standards Track                     [Page 26]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   STORAGE NODE       iSCSI Name                   *      *        *
                      iSCSI Node Type                     *        *
                      Alias                               *
                      iSCSI SCN Bitmap                    *
                      iSCSI Node Index                    *
                      WWNN Token
                      iSCSI AuthMethod
                      iSCSI Node Certificate

   DISCOVERY DOMAIN   DD ID                        *      *        *
                      DD Symbolic Name                    *
                      DD Member iSCSI Node Index          *
                      DD Member iSCSI Name                *
                      DD Member Portal Index              *
                      DD Member Portal IP Addr            *
                      DD Member Portal TCP/UDP            *
                      DD Features                         *

   DISCOVERY DOMAIN   DDS Identifier                *     *
   SET                DDS Symbolic Name                   *
                      DDS Status                          *

   All iSCSI user-specified and vendor-specified attributes are OPTIONAL
   to implement and use.



























Tseng, et al.              Standards Track                     [Page 27]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


4.1.2.  Examples: iSCSI Object Model Diagrams

   The following diagram models how a simple iSCSI-based initiator and
   target is represented using database objects stored in the iSNS
   server.  In this implementation, each target and initiator is
   attached to a single Portal.

   +----------------------------------------------------------------+
   |                         IP Network                             |
   +------------+--------------------------------------+------------+
                |                                      |
                |                                      |
   +-----+------+------+-----+            +-----+------+------+-----+
   |     | PORTAL      |     |            |     | PORTAL      |     |
   |     | -IP Addr 1  |     |            |     | -IP Addr 2  |     |
   |     | -TCP Port 1 |     |            |     | -TCP Port 2 |     |
   |     +-----+ +-----+     |            |     +-----+ +-----+     |
   |           | |           |            |           | |           |
   |     +-----+ +-----+     |            |     +-----+ +-----+     |
   |     | PORTAL GROUP|     |            |     | PORTAL GROUP|     |
   |     | -Prtl Tag 1 |     |            |     | -Prtl Tag 2 |     |
   |     +-----+ +-----+     |            |     +-----+ +-----+     |
   |           | |           |            |           | |           |
   |  +--------+ +--------+  |            |   +-------+ +--------+  |
   |  |                   |  |            |   |                  |  |
   |  |  STORAGE NODE     |  |            |   |  STORAGE NODE    |  |
   |  |  -iSCSI Name      |  |            |   |   -iSCSI Name    |  |
   |  |  -Alias: "server1"|  |            |   |   -Alias: "disk1"|  |
   |  |  -Type: initiator |  |            |   |   -Type: target  |  |
   |  |                   |  |            |   |                  |  |
   |  +-------------------+  |            |   +------------------+  |
   |                         |            |                         |
   |    NETWORK ENTITY       |            |    NETWORK ENTITY       |
   |   -Entity ID (FQDN):    |            |   -Entity ID (FQDN):    |
   |    "strg1.example.com"  |            |    "strg2.example.net"  |
   |   -Protocol: iSCSI      |            |   -Protocol: iSCSI      |
   |                         |            |                         |
   +-------------------------+            +-------------------------+

   The object model can be expanded to describe more complex devices,
   such as an iSCSI device with more than one storage controller, in
   which each controller is accessible through any of multiple Portal
   interfaces, possibly using multiple Portal Groups.  The storage
   controllers on this device can be accessed through alternate Portal
   interfaces if any original interface should fail.  The following
   diagram describes such a device:





Tseng, et al.              Standards Track                     [Page 28]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


      +---------------------------------------------------------------+
      |                         IP Network                            |
      +-------------------+-----------------------+-------------------+
                          |                       |
                          |                       |
      +------------+------+------+---------+------+------+------------+
      |            | PORTAL 1    |         | PORTAL 2    |            |
      |            | -IP Addr 1  |         | -IP Addr 2  |            |
      |            | -TCP Port 1 |         | -TCP Port 2 |            |
      |            +-----+ +-----+         +-----+ +-----+            |
      |                  | |                     | |                  |
      |  +---------------+ +---------------------+ +---------------+  |
      |  +-------+ +----------------+ +-------------------+ +------+  |
      |          | |                | |                   | |         |
      |  +-------+ +-------+ +------+ +--------+ +--------+ +------+  |
      |  |                 | |                 | |                 |  |
      |  | STORAGE NODE 1  | | STORAGE NODE 2  | | STORAGE NODE 3  |  |
      |  |  -iSCSI Name 1  | |  -iSCSI Name 2  | |  -iSCSI Name 3  |  |
      |  |  -Alias: "disk1"| |  -Alias: "disk2"| |  -Alias: "disk3"|  |
      |  |  -Type: target  | |  -Type: target  | |  -Type: target  |  |
      |  |                 | |                 | |                 |  |
      |  +-----------------+ +-----------------+ +-----------------+  |
      |                                                               |
      |                         NETWORK ENTITY                        |
      |                    -Entity ID (FQDN): "dev1.example.com"      |
      |                    -Protocol: iSCSI                           |
      |                                                               |
      |                   Portal Group Object Table                   |
      |           Storage-Node Portal Portal-Group-Tag                |
      |                1         1           10                       |
      |                1         2         NULL (no access permitted) |
      |                2         1           20                       |
      |                2         2           20                       |
      |                3         1           30                       |
      |                3         2           10                       |
      |                                                               |
      +---------------------------------------------------------------+

   Storage Node 1 is accessible via Portal 1 with a PGT of 10.  It does
   not have a Portal Group Tag (PGT) assigned for Portal 2, so Storage
   Node 1 cannot be accessed via Portal 2.

   Storage Node 2 can be accessed via both Portal 1 and Portal 2.  Since
   Storage Node 2 has the same PGT value assigned to both Portal 1 and
   Portal 2, in this case 20, coordinated access via the Portals is
   available [iSCSI].





Tseng, et al.              Standards Track                     [Page 29]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   Storage Node 3 can be accessed via Portal 1 or Portal 2.  However,
   since Storage Node 3 has different PGT values assigned to each
   Portal, in this case 10 and 30, access is not coordinated [iSCSI].
   Because PGTs are assigned within the context of a Storage Node, the
   PGT value of 10 used for Storage Node 1 and Storage Node 3 are not
   interrelated.

4.1.3.  Required Commands and Response Messages for Support of iSCSI

   The following iSNSP messages and responses are available in support
   of iSCSI.  Messages indicated in the REQUIRED for Server column MUST
   be implemented in iSNS servers used for iSCSI devices.  Messages
   indicated in the REQUIRED for Client column MUST be implemented in
   iSCSI devices that elect to use the iSNS server.

                                                     REQUIRED for:
   Message Description       Abbreviation  Func_ID   Server  Client
   -------------------       ------------  -------   ------  ------
   RESERVED                                0x0000
   Device Attr Reg Request   DevAttrReg    0x0001       *       *
   Dev Attr Query Request    DevAttrQry    0x0002       *       *
   Dev Get Next Request      DevGetNext    0x0003       *
   Deregister Dev Request    DevDereg      0x0004       *       *
   SCN Register Request      SCNReg        0x0005       *
   SCN Deregister Request    SCNDereg      0x0006       *
   SCN Event                 SCNEvent      0x0007       *
   State Change Notification SCN           0x0008       *
   DD Register               DDReg         0x0009       *       *
   DD Deregister             DDDereg       0x000A       *       *
   DDS Register              DDSReg        0x000B       *       *
   DDS Deregister            DDSDereg      0x000C       *       *
   Entity Status Inquiry     ESI           0x000D       *
   Name Service Heartbeat    Heartbeat     0x000E
   RESERVED                                0x000F-0x00FF
   Vendor Specific                         0x0100-0x01FF
   RESERVED                                0x0200-0x7FFF

   The following are iSNSP response messages used in support of iSCSI:

                                                      REQUIRED for:
   Response Message Desc     Abbreviation  Func_ID    Server  Client
   ---------------------     ------------  -------    ------  ------
   RESERVED                                0x8000
   Device Attr Register Rsp  DevAttrRegRsp 0x8001       *       *
   Device Attr Query Rsp     DevAttrQryRsp 0x8002       *       *
   Device Get Next Rsp       DevGetNextRsp 0x8003       *
   Device Dereg Rsp          DevDeregRsp   0x8004       *       *
   SCN Register Rsp          SCNRegRsp     0x8005       *



Tseng, et al.              Standards Track                     [Page 30]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   SCN Deregister Rsp        SCNDeregRsp   0x8006       *
   SCN Event Rsp             SCNEventRsp   0x8007       *
   SCN Response              SCNRsp        0x8008       *
   DD Register Rsp           DDRegRsp      0x8009       *       *
   DD Deregister Rsp         DDDeregRsp    0x800A       *       *
   DDS Register Rsp          DDSRegRsp     0x800B       *       *
   DDS Deregister Rsp        DDSDeregRsp   0x800C       *       *
   Entity Stat Inquiry Rsp   ESIRsp        0x800D       *
   RESERVED                                0x800E-0x80FF
   Vendor Specific                         0x8100-0x81FF
   RESERVED                                0x8200-0xFFFF

4.2.  iFCP Requirements

   In iFCP, use of iSNS is REQUIRED.  No alternatives exist for support
   of iFCP Naming & Discovery functions.

4.2.1.  Required Attributes for Support of iFCP

   The following table displays attributes that are used by iSNS to
   support iFCP.  Attributes indicated in the REQUIRED for Server column
   MUST be implemented by the iSNS server that supports iFCP.
   Attributes indicated in the REQUIRED for Client column MUST be
   supported by iFCP gateways.  Attributes indicated in the K (Key)
   column uniquely identify the object type in the iSNS Server.  A more
   detailed description of each attribute is found in Section 6.

                                                       REQUIRED for:
   Object             Attribute                   K    Server  Client
   ------             ---------                   -    ------  ------
   NETWORK ENTITY     Entity Identifier           *       *       *
                      Entity Protocol                     *       *
                      Management IP Address               *
                      Timestamp                           *
                      Protocol Version Range              *
                      Registration period
                      Entity Index
                      Entity IKE Phase-1 Proposal
                      Entity Certificate

   PORTAL             IP Address                  *       *       *
                      TCP/UDP Port                *       *       *
                      Symbolic Name                       *
                      ESI Interval                        *
                      ESI Port                            *
                      SCN Port                            *
                      Portal IKE Phase-1 Proposal
                      Portal IKE Phase-2 Proposal



Tseng, et al.              Standards Track                     [Page 31]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


                      Portal Certificate
                      Security Bitmap                     *

   STORAGE NODE       FC Port Name (WWPN)         *       *       *
   (FC Port)          Port_ID                             *       *
                      FC Port Type                        *       *
                      Port Symbolic Name                  *
                      Fabric Port Name (FWWN)             *
                      Hard Address                        *
                      Port IP Address                     *
                      Class of Service                    *
                      FC FC-4 Types                       *
                      FC FC-4 Descriptors                 *
                      FC FC-4 Features                    *
                      SCN Bitmap                          *
                      iFCP Port Role                      *
                      Permanent Port Name                 *

   FC DEVICE          FC Node Name (WWNN)         *       *       *
   (FC Node)          Node Symbolic Name                  *
                      Node IP Address                     *
                      Node IPA                            *
                      Proxy iSCSI Name

   DISCOVERY DOMAIN   DD ID                       *       *       *
                      DD Symbolic Name                    *
                      DD Member FC Port Name              *
                      DD Member Portal Index              *
                      DD Member Portal IP Addr            *
                      DD Member Portal TCP/UDP            *

   DISCOVERY DOMAIN   DDS ID                      *       *
   SET                DDS Symbolic Name                   *
                      DDS Status                          *

   OTHER              Switch Name
                      Preferred_ID
                      Assigned_ID
                      Virtual_Fabric_ID

   All iFCP user-specified and vendor-specified attributes are OPTIONAL
   to implement and use.

4.2.2.  Example: iFCP Object Model Diagram

   The iFCP protocol allows native Fibre Channel devices or Fibre
   Channel fabrics connected to an iFCP gateway to be directly
   internetworked using IP.



Tseng, et al.              Standards Track                     [Page 32]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   When supporting iFCP, the iSNS server stores Fibre Channel device
   attributes, iFCP gateway attributes, and Fibre Channel fabric switch
   attributes that might also be stored in an FC name server.

   The following diagram shows a representation of a gateway supporting
   multiple Fibre Channel devices behind it.  The two Portal objects
   represent IP interfaces on the iFCP gateway that can be used to
   access any of the three Storage Node objects behind it.  Note that
   the FC Device object is not contained in the Network Entity object.
   However, each FC Device has a relationship to one or more Storage
   Node objects.

   +--------------------------------------------------------+
   |                         IP Network                     |
   +--------+-----------------+-----------------------------+
            |                 |
   +-+------+------+---+------+------+----------------------+
   | | PORTAL      |   | PORTAL      | NETWORK ENTITY       |
   | | -IP Addr 1  |   | -IP Addr 2  | -Entity ID (FQDN):   |
   | | -TCP Port 1 |   | -TCP Port 2 |  "gtwy1.example.com" |
   | +-----+ +-----+   +-----+ +-----+ -Protocol: iFCP      |
   |       | |               | |                            |
   | +-----+ +---------------+ +----------------------+     |
   | +-----+ +---------------+ +-------------+ +------+     |
   |       | |               | |             | |            |
   | +-----+ +-----+    +----+ +------+ +----+ +------+     |
   | |STORAGE NODE |    |STORAGE NODE | |STORAGE NODE |     |
   | | -WWPN 1     |    | -WWPN 2     | | -WWPN 3     |     |
   | | -Port ID 1  |    | -Port ID 2  | | -Port ID 3  |     |
   | | -FWWN 1     |    | -FWWN 2     | | -FWWN 3     |     |
   | | -FC COS     |    | -FC COS     | | -FC COS     |     |
   | +------+------+    +-------+-----+ +----+--------+     |
   +--------|-------------------|------------|--------------+
            |                   |            |
     +------+------+        +---+------------+---+
     | FC DEVICE   |        |    FC DEVICE       |
     | -WWNN 1     |        |   -WWNN 2          |
     |             |        |                    |
     +-------------+        +--------------------+












Tseng, et al.              Standards Track                     [Page 33]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


4.2.3.  Required Commands and Response Messages for Support of iFCP

   The iSNSP messages and responses displayed in the following tables
   are available to support iFCP gateways.  Messages indicated in the
   REQUIRED TO IMPLEMENT column MUST be supported by the iSNS server
   used by iFCP gateways.  Messages indicated in the REQUIRED TO USE
   column MUST be supported by the iFCP gateways themselves.

                                                     REQUIRED for:
   Message Description       Abbreviation  Func ID   Server   Client
   -------------------       ------------  -------   ------   ------
   RESERVED                                0x0000
   Device Attr Reg Request   DevAttrReg    0x0001       *       *
   Device Attr Query Request DevAttrQry    0x0002       *       *
   Device Get Next Request   DevGetNext    0x0003       *
   Device Dereg Request      DevDereg      0x0004       *       *
   SCN Register Request      SCNReg        0x0005       *
   SCN Deregister Request    SCNDereg      0x0006       *
   SCN Event                 SCNEvent      0x0007       *
   State Change Notification SCN           0x0008       *
   DD Register               DDReg         0x0009       *       *
   DD Deregister             DDDereg       0x000A       *       *
   DDS Register              DDSReg        0x000B       *       *
   DDS Deregister            DDSDereg      0x000C       *       *
   Entity Status Inquiry     ESI           0x000D       *
   Name Service Heartbeat    Heartbeat     0x000E       *
   Reserved                  Reserved      0x000F-0x0010
   Request FC_DOMAIN_ID      RqstDomId     0x0011
   Release FC_DOMAIN_ID      RlseDomId     0x0012
   Get FC_DOMAIN_IDs         GetDomId      0x0013
   RESERVED                                0x0014-0x00FF
   Vendor Specific                         0x0100-0x01FF
   RESERVED                                0x0200-0x7FFF

   The following are iSNSP response messages in support of iFCP:

                                                     REQUIRED for:
   Response Message Desc     Abbreviation  Func_ID   Server   Client
   ---------------------     ------------  -------   ------   ------
   RESERVED                                0x8000
   Device Attr Reg Rsp       DevAttrRegRsp 0x8001       *       *
   Device Attr Query Rsp     DevAttrQryRsp 0x8002       *       *
   Device Get Next Rsp       DevGetNextRsp 0x8003       *
   Device Deregister Rsp     DevDeregRsp   0x8004       *       *
   SCN Register Rsp          SCNRegRsp     0x8005       *
   SCN Deregister Rsp        SCNDeregRsp   0x8006       *
   SCN Event Rsp             SCNEventRsp   0x8007       *
   SCN Rsp                   SCNRsp        0x8008       *



Tseng, et al.              Standards Track                     [Page 34]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   DD Register Rsp           DDRegRsp      0x8009       *       *
   DD Deregister Rsp         DDDeregRsp    0x800A       *       *
   DDS Register Rsp          DDSRegRsp     0x800B       *       *
   DDS Deregister Rsp        DDSDeregRsp   0x800C       *       *
   Entity Status Inquiry Rsp ESIRsp        0x800D       *
   NOT USED                                0x800E
   RESERVED                                0x800F-0x8010
   Request FC_DOMAIN_ID Rsp  RqstDomIdRsp  0x8011
   Release FC_DOMAIN_ID Rsp  RlseDomIdRsp  0x8012
   Get FC_DOMAIN_IDs         GetDomIdRsp   0x0013
   RESERVED                                0x8014-0x80FF
   Vendor Specific                         0x8100-0x81FF
   RESERVED                                0x8200-0xFFFF

5.  iSNSP Message Format

   The iSNSP message format is similar to the format of other common
   protocols such as DHCP, DNS and BOOTP.  An iSNSP message may be sent
   in one or more iSNS Protocol Data Units (PDU).  Each PDU is 4-byte
   aligned.  The following describes the format of the iSNSP PDU:

   Byte   MSb                                        LSb
   Offset 0                   15 16                   31
          +---------------------+----------------------+
        0 |   iSNSP VERSION     |    FUNCTION ID       | 4 Bytes
          +---------------------+----------------------+
        4 |     PDU LENGTH      |       FLAGS          | 4 Bytes
          +---------------------+----------------------+
        8 |   TRANSACTION ID    |    SEQUENCE ID       | 4 Bytes
          +---------------------+----------------------+
       12 |                                            |
          |                PDU PAYLOAD                 | N Bytes
          |                    ...                     |
          +--------------------------------------------+
     12+N | AUTHENTICATION BLOCK (Multicast/Broadcast) | L Bytes
          +--------------------------------------------+
                   Total Length = 12 + N + L

5.1.  iSNSP PDU Header

   The iSNSP PDU header contains the iSNSP VERSION, FUNCTION ID, PDU
   LENGTH, FLAGS, TRANSACTION ID, and SEQUENCE ID fields as defined
   below.








Tseng, et al.              Standards Track                     [Page 35]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


5.1.1.  iSNSP Version

   The iSNSP version described in this document is 0x0001.  All other
   values are RESERVED.  The iSNS server MAY reject messages for iSNSP
   version numbers that it does not support.

5.1.2.  iSNSP Function ID

   The FUNCTION ID defines the type of iSNS message and the operation to
   be executed.  FUNCTION_ID values with the leading bit cleared
   indicate query, registration, and notification messages, whereas
   FUNCTION_ID values with the leading bit set indicate response
   messages.

   See Section 4 under the appropriate protocol (i.e., iSCSI or iFCP)
   for a mapping of the FUNCTION_ID value to the iSNSP Command or
   Response message.  All PDUs comprising an iSNSP message must have the
   same FUNCTION_ID value.

5.1.3.  iSNSP PDU Length

   The iSNS PDU Length specifies the length of the PDU PAYLOAD field in
   bytes.  The PDU Payload contains TLV attributes for the operation.

   Additionally, response messages contain a success/failure code.  The
   PDU Length MUST be 4-byte aligned.

5.1.4.  iSNSP Flags

   The FLAGS field indicates additional information about the message
   and the type of Network Entity that generated the message.  The
   following table displays the valid flags:

          Bit Position      Enabled (1) means:
          ------------      -----------------
           16               Sender is the iSNS client
           17               Sender is the iSNS server
           18               Authentication block is present
           19               Replace flag (for DevAttrReg)
           20               Last PDU of the iSNS message
           21               First PDU of the iSNS message
           22-31            RESERVED

5.1.5.  iSNSP Transaction ID

   The TRANSACTION ID MUST be set to a unique value for each
   concurrently outstanding request message.  Replies MUST use the same
   TRANSACTION ID value as the associated iSNS request message.  If a



Tseng, et al.              Standards Track                     [Page 36]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   message is retransmitted, the original TRANSACTION ID value MUST be
   used.  All PDUs comprising an iSNSP message must have the same
   TRANSACTION ID value.

5.1.6.  iSNSP Sequence ID

   The SEQUENCE ID has a unique value for each PDU within a single
   transaction.  The SEQUENCE_ID value of the first PDU transmitted in a
   given iSNS message MUST be zero (0), and each SEQUENCE_ID value in
   each PDU MUST be numbered sequentially in the order in which the PDUs
   are transmitted.  Note that the two-byte SEQUENCE ID allows for up to
   65536 PDUs per iSNS message.

5.2.  iSNSP Message Segmentation and Reassembly

   iSNS messages may be carried in one or more iSNS PDUs.  If only one
   iSNS PDU is used to carry the iSNS message, then bit 21 (First PDU)
   and bit 20 in the FLAGS field (Last PDU) SHALL both be set.  If
   multiple PDUs are used to carry the iSNS message, then bit 21 SHALL
   be set in the first PDU of the message, and bit 20 SHALL be set in
   the last PDU.

   All PDUs comprising the same iSNSP message SHALL have the same
   FUNCTION_ID and TRANSACTION_ID values.  Each PDU comprising an iSNSP
   message SHALL have a unique SEQUENCE_ID value.

5.3.  iSNSP PDU Payload

   The iSNSP PDU PAYLOAD is of variable length and contains attributes
   used for registration and query operations.  The attribute data items
   use a format similar to that of other protocols, such as DHCP
   [RFC2131] options.  Each iSNS attribute is specified in the PDU
   Payload using Tag-Length-Value (TLV) data format, as shown below:

   Byte   MSb                                        LSb
   Offset 0                                           31
          +--------------------------------------------+
        0 |               Attribute Tag                | 4 Bytes
          +--------------------------------------------+
        4 |            Attribute Length (N)            | 4 Bytes
          +--------------------------------------------+
        8 |                                            |
          |              Attribute Value               | N Bytes
          |                                            |
          +--------------------------------------------+
                   Total Length = 8 + N





Tseng, et al.              Standards Track                     [Page 37]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   Attribute Tag:    a 4-byte field that identifies the attribute as
                     defined in Section 6.1.  This field contains the
                     tag value from the indicated table.

   Attribute Length: a 4-byte field that indicates the length, in bytes,
                     of the value field to follow in the TLV.  For
                     variable-length attributes, the value field MUST
                     contain padding bytes, if necessary, in order to
                     achieve 4-byte alignment.  A "zero-length TLV"
                     contains only the attribute tag and length fields.

   Attribute Value:  a variable-length field containing the attribute
                     value and padding bytes (if necessary).

   The above format is used to identify each attribute in the PDU
   Payload.  Note that TLV boundaries need not be aligned with PDU
   boundaries; PDUs may carry one or more TLVs, or any fraction thereof.
   The Response Status Code, contained in response message PDU Payloads
   and described below, is not in TLV format.  PDU Payloads for messages
   that do not contain iSNS attributes, such as the Name Service
   Heartbeat, do not use the TLV format.

5.3.1.  Attribute Value 4-Byte Alignment

   All attribute values are aligned to 4-byte boundaries.  For variable
   length attributes, if necessary, the TLV length MUST be increased to
   the next 4-byte boundary through padding with bytes containing zero
   (0).  If an attribute value is padded, a combination of the tag and
   attribute value itself is used to determine the actual value length
   and number of pad bytes.  There is no explicit count of the number of
   pad bytes provided in the TLV.




















Tseng, et al.              Standards Track                     [Page 38]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


5.4.  iSNSP Response Status Codes

   All iSNSP response messages contain a 4-byte Status Code field as the
   first field in the iSNSP PDU PAYLOAD.  If the original iSNSP request
   message was processed normally by the iSNS server, or by the iSNS
   client for ESI and SCN messages, then this field SHALL contain a
   status code of 0 (Successful).  A non-zero status code indicates
   rejection of the entire iSNS client request message.

          Status Code      Status Description
          -----------      -----------------
            0              Successful
            1              Unknown Error
            2              Message Format Error
            3              Invalid Registration
            4              RESERVED
            5              Invalid Query
            6              Source Unknown
            7              Source Absent
            8              Source Unauthorized
            9              No Such Entry
           10              Version Not Supported
           11              Internal Error
           12              Busy
           13              Option Not Understood
           14              Invalid Update
           15              Message (FUNCTION_ID) Not Supported
           16              SCN Event Rejected
           17              SCN Registration Rejected
           18              Attribute Not Implemented
           19              FC_DOMAIN_ID Not Available
           20              FC_DOMAIN_ID Not Allocated
           21              ESI Not Available
           22              Invalid Deregistration
           23              Registration Feature Not Supported
           24 and above    RESERVED

5.5.  Authentication for iSNS Multicast and Broadcast Messages

   For iSNS multicast and broadcast messages (see Section 2.9.3), the
   iSNSP provides authentication capability.  The following section
   details the iSNS Authentication Block, which is identical in format
   to the SLP authentication block [RFC2608]. iSNS unicast messages
   SHOULD NOT include the authentication block, but rather should rely
   upon IPSec security mechanisms.






Tseng, et al.              Standards Track                     [Page 39]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   If a message contains an authentication block, then the
   "Authentication block present" bit in the iSNSP PDU header FLAGS
   field SHALL be enabled.

   If a PKI is available with an [X.509] Certificate Authority (CA),
   then public key authentication of the iSNS server is possible.  The
   authentication block leverages the DSA with SHA-1 algorithm, which
   can easily integrate into a public key infrastructure.

   The authentication block contains a digital signature for the
   multicast message.  The digital signature is calculated on a per-PDU
   basis.  The authentication block contains the following information:

   1.  A time stamp, to prevent replay attacks.
   2.  A structured authenticator containing a signature calculated over
       the time stamp and the message being secured.
   3.  An indicator of the cryptographic algorithm that was used to
       calculate the signature.
   4.  An indicator of the keying material and algorithm parameters,
       used to calculate the signature.

   The authentication block is described in the following figure:

      Byte   MSb                              LSb
      Offset 0                                 31
             +----------------------------------+
         0   |    BLOCK STRUCTURE DESCRIPTOR    |     4 Bytes
             +----------------------------------+
         4   |   AUTHENTICATION BLOCK LENGTH    |     4 Bytes
             +----------------------------------+
         8   |           TIMESTAMP              |     8 Bytes
             +----------------------------------+
        16   |       SPI STRING LENGTH          |     4 Bytes
             +----------------------------------+
        20   |           SPI STRING             |     N Bytes
             +----------------------------------+
    20 + N   |     STRUCTURED AUTHENTICATOR     |     M Bytes
             +----------------------------------+
                Total Length = 20 + N + M

   BLOCK STRUCTURE DESCRIPTOR (BSD): Defines the structure and algorithm
              to use for the STRUCTURED AUTHENTICATOR.  BSD values from
              0x00000000 to 0x00007FFF are assigned by IANA, while
              values 0x00008000 to 0x00008FFF are for private use.







Tseng, et al.              Standards Track                     [Page 40]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   AUTHENTICATION BLOCK LENGTH: Defines the length of the authentication
              block, beginning with the BSD field and running through
              the last byte of the STRUCTURED AUTHENTICATOR.

   TIMESTAMP: This is an 8-byte unsigned, fixed-point integer giving the
              number of seconds since 00:00:00 GMT on January 1, 1970.

   SPI STRING LENGTH: The length of the SPI STRING field.

   SPI STRING (Security Parameters Index): Index to the key and
              algorithm used by the message recipient to decode the
              STRUCTURED AUTHENTICATOR field.

   STRUCTURED AUTHENTICATOR: Contains the digital signature.  For the
              default BSD value of 0x0002, this field SHALL contain the
              binary ASN.1 encoding of output values from the DSA with
              SHA-1 signature calculation as specified in Section 2.2.2
              of [RFC3279].

5.6.  Registration and Query Messages

   The iSNSP registration and query message PDU Payloads contain a list
   of attributes, and have the following format:

             +----------------------------------------+
             |     Source Attribute (Requests Only)   |
             +----------------------------------------+
             |  Message Key Attribute[1] (if present) |
             +----------------------------------------+
             |  Message Key Attribute[2] (if present) |
             +----------------------------------------+
             |               . . .                    |
             +----------------------------------------+
             |       - Delimiter Attribute -          |
             +----------------------------------------+
             |   Operating Attribute[1] (if present)  |
             +----------------------------------------+
             |   Operating Attribute[2] (if present)  |
             +----------------------------------------+
             |   Operating Attribute[3] (if present)  |
             +----------------------------------------+
             |                 . . .                  |
             +----------------------------------------+

   Each Source, Message Key, Delimiter, and Operating attribute is
   specified in the PDU Payload using the Tag-Length-Value (TLV) data
   format. iSNS Registration and Query messages are sent by iSNS Clients




Tseng, et al.              Standards Track                     [Page 41]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   to the iSNS server IP Address and well-known TCP/UDP Port.  The iSNS
   Responses will be sent to the iSNS Client IP address and TCP/UDP port
   number from the original request message.

5.6.1.  Source Attribute

   The Source Attribute is used to identify the Storage Node to the iSNS
   server for queries and other messages that require source
   identification.  The Source Attribute uniquely identifies the source
   of the message.  Valid Source Attribute types are shown below.

          Valid Source Attributes
          -----------------------
           iSCSI Name
           FC Port Name WWPN

   For a query operation, the Source Attribute is used to limit the
   scope of the specified operation to the Discovery Domains of which
   the source is a member.  Special Control Nodes, identified by the
   Source Attribute, may be administratively configured to perform the
   specified operation on all objects in the iSNS database without
   scoping to Discovery Domains.

   For messages that change the contents of the iSNS database, the iSNS
   server MUST verify that the Source Attribute identifies either a
   Control Node or a Storage Node that is a part of the Network Entity
   containing the added, deleted, or modified objects.

5.6.2.  Message Key Attributes

   Message Key attributes are used to identify matching objects in the
   iSNS database for iSNS query and registration messages.  If present,
   the Message Key MUST be a Registration or Query Key for an object as
   described in Sections 5.6.5 and 6.1.  A Message Key is not required
   when a query spans the entire set of objects available to the Source
   or a registration is for a new Entity.

   iSCSI Names used in the Message Key MUST be normalized according to
   the stringprep template [STRINGPREP].  Entity Identifiers (EIDs) used
   in the Message Key MUST be normalized according to the nameprep
   template [NAMEPREP].

5.6.3.  Delimiter Attribute

   The Delimiter Attribute separates the Message Key attributes from the
   Operating Attributes in a PDU Payload.  The Delimiter Attribute has a
   tag value of 0 and a length value of 0.  The Delimiter Attribute is
   always 8 bytes long (a 4-byte tag field and a 4-byte length field,



Tseng, et al.              Standards Track                     [Page 42]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   all containing zeros).  If a Message Key is not required for a
   message, then the Delimiter Attribute immediately follows the Source
   Attribute.

5.6.4.  Operating Attributes

   The Operating Attributes are a list of one or more key and non-key
   attributes related to the actual iSNS registration or query operation
   being performed.

   Operating Attributes include object key attributes and non-key
   attributes.  Object key attributes uniquely identify iSNS objects.
   Key attributes MUST precede the non-key attributes of each object in
   the Operating Attributes.  The tag value distinguishes the attribute
   as an object key attribute (i.e., tag=1, 16&17, 32, 64, and 96) or a
   non-key attribute. iSCSI Names used in the Operating Attributes MUST
   be normalized according to the stringprep template [STRINGPREP].
   Entity Identifiers (EIDs) used in the Operating Attributes MUST be
   normalized according to the nameprep template [NAMEPREP].

   The ordering of Operating Attributes in the message is important for
   determining the relationships among objects and their ownership of
   non-key attributes.  iSNS protocol messages that violate these
   ordering rules SHALL be rejected with the Status Code of 2 (Message
   Format Error).  See the message descriptions for proper operating
   attribute ordering requirements.

   Some objects are keyed by more than one object key attribute value.
   For example, the Portal object is keyed by attribute tags 16 and 17.
   When describing an object keyed by more than one key attribute, every
   object key attribute of that object MUST be listed sequentially by
   tag value in the message before non-key attributes of that object and
   key attributes of the next object.  A group of key attributes of this
   kind is treated as a single logical key attribute when identifying an
   object.

   Non-key attributes that immediately follow key attributes MUST be
   attributes of the object referenced by the key attributes.  All non-
   key attributes of an object MUST be listed before the object key
   attributes introducing the next object.

   Objects MUST be listed in inheritance order, according to their
   containment order.  Storage Node and Portal objects and their
   respective attributes MUST follow the Network Entity object to which
   they have a relationship.  Similarly, FC Device objects MUST follow
   the Storage Node object to which they have a relationship.





Tseng, et al.              Standards Track                     [Page 43]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   Vendor-specific objects defined by tag values in the range 1537-2048
   have the same requirements described above.

5.6.4.1.  Operating Attributes for Query and Get Next Requests

   In Query and Get Next request messages, TLV attributes with length
   value of 0 are used to indicate which Operating Attributes are to be
   returned in the corresponding response.  Operating Attribute values
   that match the TLV attributes in the original message are returned in
   the response message.

5.6.5.  Registration and Query Request Message Types

   The following describes each query and message type.

5.6.5.1.  Device Attribute Registration Request (DevAttrReg)

   The DevAttrReg message type is 0x0001.  The DevAttrReg message
   provides the means for iSNS clients to update existing objects or
   register new objects.  The value of the replace bit in the FLAGs
   field determines whether the DevAttrReg message updates or replaces
   an existing registration.

   The Source Attribute identifies the Node initiating the registration
   request.

   The Message Key identifies the object the DevAttrReg message acts
   upon.  It MUST contain the key attribute(s) identifying an object.
   This object MUST contain all attributes and related subordinate
   object attributes that will be included in the Operating Attributes
   of the DevAttrReg PDU Payload.  The key attribute(s) identifying this
   object MUST also be included among the Operating Attributes.

   If the Message Key contains an EID and no pre-existing objects match
   the Message Key, then the DevAttrReg message SHALL create a new
   Entity with the specified EID and any new object(s) specified by the
   Operating Attributes.  The replace bit SHALL be ignored.

   If the Message Key does not contain an EID, and no pre-existing
   objects match the Message Key, then the DevAttrReg message SHALL be
   rejected with a status code of 3 (Invalid Registration).

   If the Message Key is not present, then the DevAttrReg message
   implicitly registers a new Network Entity.  In this case, the replace
   bit SHALL be ignored; a new Network Entity SHALL be created.
   Existing entities, their objects, and their relationships remain
   unchanged.




Tseng, et al.              Standards Track                     [Page 44]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   The replace bit determines the kind of operation conducted on the
   object identified in the DevAttrReg Message Key.  The replace bit
   only applies to the DevAttrReg message; it is ignored for all other
   message types.

   If the replace bit is set, then the objects, attributes, and
   relationships specified in the Operating Attributes SHALL replace the
   object identified by the Message Key.  The object and all of its
   subordinate objects SHALL be deregistered, and the appropriate SCNs
   SHALL be sent by the iSNS server for the deregistered objects.  The
   objects listed in the Operating Attributes are then used to replace
   the just-deregistered objects.  Note that additional SCNs SHALL be
   sent for the newly-registered objects, if appropriate.  Existing
   objects and relationships that are not identified or that are
   subordinate to the object identified by the Message Key MUST NOT be
   affected or changed.

   If the replace bit is not set, then the message updates the
   attributes of the object identified by the Message Key and its
   subordinate objects.  Existing object containment relationships MUST
   NOT be changed.  For existing objects, key attributes MUST NOT be
   modified, but new subordinate objects MAY be added.

   The Operating Attributes represent objects, attributes, and
   relationships that are to be registered.  Multiple related objects
   and attributes MAY be registered in a single DevAttrReg message.  The
   ordering of the objects in this message indicates the structure of,
   and associations among, the objects to be registered.  At least one
   object MUST be listed in the Operating Attributes.  Additional
   objects (if any) MUST be subordinate to the first object listed.  Key
   attributes MUST precede non-key attributes of each object.  A given
   object may only appear a maximum of once in the Operating Attributes
   of a message.  If the Node identified by the Source Attribute is not
   a Control Node, then the objects in the operating attributes MUST be
   members of the same Network Entity as the Source Node.

   For example, to establish relationships between a Network Entity
   object and its Portal and Storage Node objects, the Operating
   Attributes list the key and non-key attributes of the Network Entity
   object, followed by the key and non-key attributes of each Portal and
   Storage Node object to be linked to that Network Entity.  Similarly,
   an FC Device object that follows a Storage Node object is considered
   subordinate to that Storage Node.

   New PG objects are registered when an associated Portal or iSCSI Node
   object is registered.  An explicit PG object registration MAY follow
   a Portal or iSCSI Node object registration in a DevAttrReg message.




Tseng, et al.              Standards Track                     [Page 45]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   When a Portal is registered, the Portal attributes MAY immediately be
   followed by a PGT attribute.  The PGT attribute SHALL be followed by
   the set of PG iSCSI Names representing nodes that will be associated
   to the Portal using the indicated PGT value.  Additional sets of PGTs
   and PG iSCSI Names to be associated to the registered Portal MAY
   follow.  Indicated PGT values are assigned to the PG object
   associated with the newly registered Portal and to the iSCSI Storage
   Node(s) referenced immediately following the PGT attribute in the
   operating attributes.

   When an iSCSI Storage Node is registered, the Storage Node attributes
   MAY immediately be followed by a PGT attribute.  The PGT attribute
   SHALL be followed by the set of PG Portal IP-Address, PG TCP/UDP Port
   pairs representing Portal objects that will be associated with the
   Storage Node using the indicated PGT value.  Additional sets of PGTs
   and PG Portal IP-Address PG TCP/UDP Port pairs to be associated with
   the registered Storage Node MAY follow.  Indicated PGT values are
   assigned to the PG object associated with the newly registered iSCSI
   Storage Node and Portal object(s) referenced immediately following
   the PGT attribute in the operating attributes.

   If the PGT value is not included in the Storage Node or Portal object
   registration, and if a PGT value was not previously registered for
   the relationship, then the PGT for the corresponding PG object SHALL
   be registered with a value of 0x00000001.  If the PGT attribute is
   included in the registration message as a 0-length TLV, then the PGT
   value for the corresponding PG object SHALL be registered as NULL.  A
   0-length TLV for the PGT in an update registration message overwrites
   the previous PGT value with NULL, indicating that there is no
   relationship between the Storage Node and Portal.

   A maximum of one Network Entity object can be created or updated with
   a single DevAttrReg message.  Consequently, the Operating Attributes
   MUST NOT contain more than one Network Entity object.  There is no
   limit to the number of Portal, Storage Node, and FC Device objects
   that can listed in the Operating Attributes, provided they are all
   subordinate to the listed Network Entity object.

   If the Message Key and Operating Attributes do not contain an EID
   attribute, or if the EID attribute has a length of 0, then a new
   Network Entity object SHALL be created and the iSNS server SHALL
   supply a unique EID value for it.  The assigned EID value SHALL be
   included in the DevAttrReg Response message.  If the Message Key and
   Operating Attributes contain an EID that does not match the EID of an
   existing Network Entity in the iSNS database, then a new Network
   Entity SHALL be created and assigned the value contained in that EID
   attribute.  Finally, if the Message Key and Operating Attributes
   contain an EID that matches the EID of an existing object in the iSNS



Tseng, et al.              Standards Track                     [Page 46]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   database, then the objects, attributes, and relationships specified
   in the Operating Attributes SHALL be appended to the existing Network
   Entity identified by the EID.

   A registration message that creates a new Network Entity object MUST
   contain at least one Portal or one Storage Node.  If the message does
   not, then it SHALL be considered invalid and result in a response
   with Status Code of 3 (Invalid Registration).

   If an iSNS Server does not support a registration feature, such as
   explicit PG object registration, then the server SHALL return a
   Status Code of 23 (Registration Feature Not Supported).

   Note that the iSNS server may modify or reject the registration of
   certain attributes, such as ESI Interval.  In addition, the iSNS
   server may assign values for additional Operating Attributes that are
   not explicitly registered in the original DevAttrReg message, such as
   the EID and WWNN Token.

5.6.5.2.  Device Attribute Query Request (DevAttrQry)

   The DevAttrQry message type is 0x0002.  The DevAttrQry message
   provides an iSNS client with the means to query the iSNS server for
   object attributes.

   The Source Attribute identifies the Node initiating the request.  For
   non-Control Nodes initiating the DevAttrQry message, the query is
   scoped to the Discovery Domains of which the initiating Node is a
   member.  The DevAttrQry message SHALL only return information on
   Storage Nodes and their related parent and subordinate objects, where
   the Storage Node has a common Discovery Domain with the Node
   identified in the Source Attribute.

   The Message Key may contain key or non-key attributes or no
   attributes at all.  If multiple attributes are used as the Message
   Key, then they MUST all be from the same object type (e.g., IP
   address and TCP/UDP Port are attributes of the Portal object type).
   A Message Key with non-key attributes may match multiple instances of
   the specific object type.  A Message Key with zero-length TLV(s) is
   scoped to every object of the type indicated by the zero-length
   TLV(s).  An empty Message Key field indicates the query is scoped to
   the entire database accessible by the source Node.

   The DevAttrQry response message returns attributes of objects listed
   in the Operating Attributes that are related to the Message Key of
   the original DevAttrQry message.  The Operating Attributes of the
   DevAttrQry message contain zero-length TLVs that specify the
   attributes that are to be returned in the DevAttrQryRsp message.  A



Tseng, et al.              Standards Track                     [Page 47]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   Message Key containing zero-length TLVs indicates that the set of
   attributes specified in the Operating Attributes are to be returned
   for each object matching the type indicated by the Message Key.

   If the Message Key contains non-zero length TLVs, then Operating
   Attributes for the object matching the Message Key SHALL be returned
   in the DevAttrQryRsp message.  Each attribute type (i.e., zero-length
   TLV) in the Operating Attributes indicates an attribute from the
   object matching the Message Key, or from other objects in the same
   Entity having a relationship to the object matching the Message Key,
   is to be returned in the response.  The ordering of the object keys
   and associated attributes returned in the DevAttrQry response message
   SHALL be the same as in the original query message.  If no objects
   match the Message Key, then the DevAttrQryRsp message SHALL NOT
   return any operating attributes.  Such a message and its
   corresponding response SHALL NOT be considered an error.

   The Portal Group object determines whether a relationship exists
   between a given Storage Node and Portal object.  If the PGT of the
   Portal Group is not NULL, then a relationship exists between the
   indicated Storage Node and Portal; if the PGT is NULL, then no
   relationship exists.  Therefore, the value (NULL or not NULL) of the
   PGT attribute of each Portal Group object determines the structure
   and ordering of the DevAttrQry response to a query for Storage Nodes
   and Portals.

   For example, an iSNS database contains a Network Entity having two
   Portals and two Nodes.  Each Storage Node has two Portal Groups, one
   with a NULL PGT value for one Portal and another with a non-NULL PGT
   value for the other Portal.  The DevAttrQry message contains a
   Message Key entry matching one of the Nodes, and Operating Attributes
   with zero-length TLVs listing first the Node attributes, Portal
   attributes, and then the PG attributes.  The response message SHALL
   therefore return first the matching Node object, then the requested
   attributes of the one Portal object that can be used to access the
   Storage Node (as indicated by the PGT), and finally the requested
   attributes of the PG object used to access that Storage Node.  The
   order in which each object's attributes are listed is the same as the
   ordering of the object's attributes in the Operating Attributes of
   the original request message.

   If the Message Key Attribute contains zero-length TLV(s), then the
   query returns requested attributes for all objects matching the
   Message Key type (DD restrictions SHALL apply for non-Control Nodes).
   If multiple objects match the Message Key type, then the attributes
   for each object matching the Message Key MUST be listed before the
   attributes for the next matching object are listed in the query




Tseng, et al.              Standards Track                     [Page 48]

RFC 4171          Internet Storage Name Service (iSNS)    September 2005


   response.  In other words, the process described above must be
   iterated in the message response for each object that matches the
   Message Key type specified by the zero-length TLV(s).

   For example, an iSNS database contains only one Network Entity having
   two Portals and three Nodes.  All PG objects in the Entity have a PGT
   value of 0x00000001.  In the DevAttrQry message, the Message Key
   contains a zero-length TLV specifying a Node type, and Operating
   Attributes listing first the Node attributes, and then the Portal
   attributes.  The response message will return, in the following
   order, the attributes for the first, next, and last Node objects,
   each followed by attributes for both Portals.  If that same
   DevAttrQry message had instead contained a zero-length TLV specifying
   the Network Entity type, then the response message would have
   returned attributes for all three Node objects, followed by
   attributes for the two Portals.

   If there is no Message Key Attribute, then the query returns all
   attributes in the iSNS database (once again, DD restrictions SHALL
   apply for non-Control Nodes).  All attributes matching the type
   specified by each zero-length TLV in the Operating Attributes SHALL
   be listed.  All attributes of each type SHALL be listed before the
   attributes matching the next zero-length TLV are listed.

   For example, an iSNS database contains two Entities, each having two
   Nodes and two Portals.  The DevAttrQry message contains no Message
   Key attribute, and Operating Attributes list first the Portal
   attributes, and then the Node attributes.  The Operating Attributes
   of the response message will return attributes from each of the four
   Portals, followed by attributes from each of the four nodes.

   If a DevAttrQry message requests an attribute for which the iSNS
   server has no value, then the server SHALL NOT return the requested
   attribute in the query response.  Such query and response messages
   SHALL NOT be considered errors.

   Registration and query messages for iSNS server-specific attributes
   (i.e., tags in the range 132 to 384) SHALL be formatted using the
   identifying key attribute of the Storage Node originating the query
   (i.e., iSCSI Name or FC Port Name WWPN) for both the Source Attribute
   and Message Key attribute.  Operating Attributes SHALL include the
   TLV of the server-specific attribute being requested.

   DD membership can be discovered