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iSCSI Login

 

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The iSCSI login enables:

  • A TCP connection for iSCSI use

  • Authentication of the parties

  • Negotiation of the session’s parameters

  • Marking the connection as belonging to an iSCSI session

An iSCSI session is established to identify all of the connections between an initiator and a target belonging to the same I_T nexus.

Targets listen on a well-known TCP port (3260, as defined in the iSCSI Protocol Specification), or on a user configured TCP port, for incoming connections. The initiator begins the login process by connecting to one of these TCP ports.

An iSCSI Session has two phases:

  • Login Phase

  • Full Featured Phase

Figure 1-6 iSCSI Session Establishment and Phases

iSCSI Session Establishment and Phases

Login Phase

The iSCSI Login Phase consists of Login requests and responses. Once authentication has occurred and operational parameters have been set, the session transitions to the Full Feature Phase and the initiator begins performing SCSI I/Os. NOTE: Using authentication is optional.

iSCSI parameters are negotiated using Login Requests and Responses, during session establishment. During the Full Feature Phase, iSCSI parameters are negotiated using Text Requests and Responses. In both cases the mechanism is an exchange of iSCSI-text-key=value pairs (also referred to as key=value pairs).

The Login Phase proceeds in two stages:

  • Security/Authentication Stage

    This stage consists of text exchanges using IDs, Certificates, etc., using key=value pairs.

    One of the keys that is negotiated in this stage of the Login Phase is AuthMethod. For example:

    • key=value     AuthMethod=CHAP

    • AuthMethod defines the authentication method.

  • Operational Parameters Negotiation Stage

    This stage consists of text string negotiation of operating parameters using key=value pairs of login parameter exchanges.

    Two of the many login keys that are negotiated in the Operational Parameters Negotiation stage of the Login Phase are MaxRecvDataSegmentLength and FirstBurstLength. For example:

    • key=value     MaxRecvDataSegmentLength=<numerical-value>

    • MaxRecvDataSegmentLength defines the maximum data segment length an initiator or target can receive in an iSCSI PDU (in bytes).

    • key=value     FirstBurstLength=<numerical-value>

    • FirstBurstLength defines the maximum amount of unsolicited data the initiator can send to the target during the execution of a single SCSI command (in bytes).

NOTE: For a complete list of iSCSI login keys, consult RFC 3720 at: http://www.ietf.org/rfc/rfc3720.txt

iSCSI Full Feature Phase

After successfully completing the Login Phase on the first (leading) connection of the session, a session is in Full Feature Phase.

In the Full Feature Phase, the initiator sends SCSI commands and data to the target by encapsulating them in iSCSI PDUs that go over the iSCSI session (transport). The initiator receives SCSI responses embedded in iSCSI PDUs, from the target. SCSI I/O only occurs after the Full Feature Phase begins.