network protocols handbook.pdf

235Protocols GuideSAN ProtocolsProtocol NameiSNS and iSNSP: Internet StorageName Service and iSNSProtocolProtocol DescriptioniSNS facilitates scalable configuration and management of iSC-SI and Fibre Channel (FCP) storage devices in an IP network, byproviding a set of services comparable to that available in FibreChannel networks. iSNS thus allows a commodity IP network tofunction at a comparable level of intelligence to a Fibre Channelfabric. iSNS allows the administrator to go beyond a simple device-by-devicemanagement model, where each storage deviceis manually and individually configured with its own list of knowninitiators and targets. Using the iSNS, each storage device subordinatesits discovery and management responsibilities to theiSNS server. The iSNS server thereby serves as the consolidatedconfiguration point through which management stationscan configure and manage the entire storage network, includingboth iSCSI and Fibre Channel devices.iSNS can be implemented to support iSCSI and/or iFCP protocolsas needed; an iSNS implementation MAY provide supportfor one or both of these protocols as desired by the implementer.Implementation requirements within each of these protocols arefurther discussed in section 5. Use of iSNS is OPTIONAL foriSCSI, and REQUIRED for iFCP.There are four main functions of the iSNS:1) A Name Service Providing Storage Resource Discovery2) Discovery Domain (DD) and Login Control Service3) State Change Notification Service4) Open Mapping of Fibre Channel and iSCSI DevicesiSNS has the following key Architectural Components:iSNS Protocol (iSNSP) - iSNSP is a flexible and lightweight protocolthat specifies how iSNS clients and servers communicate.It is suitable for various platforms, including switches and targetsas well as server hosts.iSNS Client - iSNS clients initiate transactions with iSNS serversusing the iSNSP. iSNS clients are processes that are coresidentin the storage device, and can register device attributeinformation, download information about other registered clientsin a common Discovery Domain (DD), and receive asynchronousnotification of events that occur in their DD(s). Managementstations are a special type of iSNS client that have accessto all DDs stored in the iSNS.iSNS Server - iSNS servers respond to iSNS protocol queriesand requests, and initiate iSNS protocol State Change Notifications.Properly authenticated information submitted by a registrationrequest is stored in an iSNS database.iSNS Database - The iSNS database is the information repositoryfor the iSNS server(s). It maintains information about iSNSclient attributes. A directory-enabled implementation of iSNSmay store client attributes in an LDAP directory infrastructure.Protocol StructureiSNSP message structure:16 32bitiSNSP versionFunction IDPDU LengthFlagsTransaction IDSequence IDPDU Payload (variable bytes)Authentication Block (variable bytes)• iSNSP Version – the current version is 0x0001. Allother values are RESERVED.• iSNSP Function ID - defines the type of iSNS messageand the operation to be executed. iSNSPPDU Length - specifies the length of the PDU PAY-LOAD field in bytes. The PDU Payload contains TLVattributes for the operation.• iSNSP Flags - indicates additional information aboutthe message and the type of Network Entity that generatedthe message.• iSNSP Transaction ID - MUST be set to a unique valuefor each concurrently outstanding request message.Replies MUST use the same TRANSACTIONID value as the associated iSNS request message.• iSNSP Sequence ID - The SEQUENCE ID has aunique value for each PDU within a single transaction.• iSNSP PDU Payload - The iSNSP PDU PAYLOADis of variable length and contains attributes used forregistration and query operations.• Authentication Block - For iSNS multicast and broadcastmessages, the iSNSP provides authenticationcapability. The iSNS Authentication Block is identicalin format to the SLP authentication block.Related protocolsiFCP, iSCSI, TCP, UDP, NAT, SNMP, SLP, DHCP, DNS,BOOTPSponsor SourceiSNS and iSNSP are defined by IET (www.ietf.org).Referencehttp://www.javvin.com/protocol/draft-ietf-ips-isns-22.pdfInternet Storage Name Service (iSNS)