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 comparable level of intelligence 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.

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

iSNS has the following key Architectural Components:

iSNS Protocol (iSNSP) - 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.

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 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.

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.

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.

• iSNSP Version C the current version is 0x0001. All other values are RESERVED.
• iSNSP Function ID - defines the type of iSNS message and the operation to be executed. iSNSP PDU Length - specifies the length of the PDU PAYLOAD field in bytes. The PDU Payload contains TLV attributes for the operation.
• iSNSP Flags - indicates additional information about the message and the type of Network Entity that generated the message.
• iSNSP 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.
• iSNSP Sequence ID - The SEQUENCE ID has a unique value for each PDU within a single transaction.
• iSNSP PDU Payload - The iSNSP PDU PAYLOAD is variable length and contains attributes used for registration and query operations.
• Authentication Block - For iSNS multicast and broadcast messages, the iSNSP provides authentication capability. The iSNS Authentication Block is identical in format to the SLP authentication block.