RFC 7145
Internet Small Computer System Interface (iSCSI) Extensions for the Remote Direct Memory Access (RDMA) Specification
3. Upper-Layer Interface Requirements
This section discusses the upper-layer interface requirements in the form of an abstract model of the required interactions between the iSCSI layer and the iSER layer. The abstract model used here is derived from the architectural model described in [DA]. [DA] also provides a functional overview of the interactions between the iSCSI layer and the Datamover layer as intended by the Datamover Architecture. The interface requirements are specified by Operational Primitives. An Operational Primitive is an abstract functional interface procedure between the iSCSI layer and the iSER layer that requests one layer to perform a specific action on behalf of the other layer or notifies the other layer of some event. Whenever an Operational Primitive in invoked, the Connection_Handle qualifier is used to identify a particular iSCSI connection. For some Operational Primitives, a Data_Descriptor is used to identify the iSCSI/SCSI data buffer associated with the requested or completed operation. The abstract model and the Operational Primitives defined in this section facilitate the description of the iSER protocol. In the rest of the iSER specification, the compliance statements related to the use of these Operational Primitives are only for the purpose of the
required interactions between the iSCSI layer and the iSER layer. Note that the compliance statements related to the Operational Primitives in the rest of this specification only mandate functional equivalence on implementations, but do not put any requirements on the implementation specifics of the interface between the iSCSI layer and the iSER layer. Each Operational Primitive is invoked with a set of qualifiers which specify the information context for performing the specific action being requested of the Operational Primitive. While the qualifiers are required, the method of realizing the qualifiers (e.g., by passing synchronously with invocation, or by retrieving from task context, or by retrieving from shared memory, etc.) is implementation dependent.3.1. Operational Primitives offered by iSER
The iSER protocol layer MUST support the following Operational Primitives to be used by the iSCSI protocol layer.3.1.1. Send_Control
Input qualifiers: Connection_Handle, BHS and AHS (if any) of the iSCSI PDU, PDU-specific qualifiers Return results: Not specified This is used by the iSCSI layers at the initiator and the target to request the outbound transfer of an iSCSI control-type PDU (see Section 7.2). Qualifiers that only apply for a particular control- type PDU are known as PDU-specific qualifiers, e.g., ImmediateDataSize for a SCSI Write command. For details on PDU- specific qualifiers, see Section 7.3. The iSCSI layer can only invoke the Send_Control Operational Primitive when the connection is in iSER-assisted mode.3.1.2. Put_Data
Input qualifiers: Connection_Handle, content of a SCSI Data-In PDU header, Data_Descriptor, Notify_Enable Return results: Not specified This is used by the iSCSI layer at the target to request the outbound transfer of data for a SCSI Data-In PDU from the buffer identified by the Data_Descriptor qualifier. The iSCSI layer can only invoke the Put_Data Operational Primitive when the connection is in iSER- assisted mode.
The Notify_Enable qualifier is used to indicate to the iSER layer whether or not it should generate an eventual local completion notification to the iSCSI layer. See Section 3.2.2 on Data_Completion_Notify for details.3.1.3. Get_Data
Input qualifiers: Connection_Handle, content of an R2T PDU, Data_Descriptor, Notify_Enable Return results: Not specified This is used by the iSCSI layer at the target to request the inbound transfer of solicited data requested by an R2T PDU into the buffer identified by the Data_Descriptor qualifier. The iSCSI layer can only invoke the Get_Data Operational Primitive when the connection is in iSER-assisted mode. The Notify_Enable qualifier is used to indicate to the iSER layer whether or not it should generate the eventual local completion notification to the iSCSI layer. See Section 3.2.2 on Data_Completion_Notify for details.3.1.4. Allocate_Connection_Resources
Input qualifiers: Connection_Handle, Resource_Descriptor (optional) Return results: Status This is used by the iSCSI layers at the initiator and the target to request the allocation of all connection resources necessary to support RCaP for an operational iSCSI/iSER connection. The iSCSI layer may optionally specify the implementation-specific resource requirements for the iSCSI connection using the Resource_Descriptor qualifier. A return result of Status=success means the invocation succeeded, and a return result of Status=failure means that the invocation failed. If the invocation is for a Connection_Handle for which an earlier invocation succeeded, the request will be ignored by the iSER layer and the result of Status=success will be returned. Only one Allocate_Connection_Resources Operational Primitive invocation can be outstanding for a given Connection_Handle at any time.
3.1.5. Deallocate_Connection_Resources
Input qualifiers: Connection_Handle Return results: Not specified This is used by the iSCSI layers at the initiator and the target to request the deallocation of all connection resources that were allocated earlier as a result of a successful invocation of the Allocate_Connection_Resources Operational Primitive.3.1.6. Enable_Datamover
Input qualifiers: Connection_Handle, Transport_Connection_Descriptor, Final Login_Response_PDU (optional) Return results: Not specified This is used by the iSCSI layers at the initiator and the target to request that iSER-assisted mode be used for the connection. The Transport_Connection_Descriptor qualifier is used to identify the specific connection associated with the Connection_Handle. The iSCSI layer can only invoke the Enable_Datamover Operational Primitive when there was a corresponding prior resource allocation. The Final_Login_Response_PDU input qualifier is applicable only for a target and contains the final Login Response PDU that concludes the iSCSI Login Phase.3.1.7. Connection_Terminate
Input qualifiers: Connection_Handle Return results: Not specified This is used by the iSCSI layers at the initiator and the target to request that a specified iSCSI/iSER connection be terminated and all associated connection and task resources be freed. When this Operational Primitive invocation returns to the iSCSI layer, the iSCSI layer may assume full ownership of all iSCSI-level resources, e.g., I/O Buffers, associated with the connection.
3.1.8. Notice_Key_Values
Input qualifiers: Connection_Handle, number of keys, list of Key- Value pairs Return results: Not specified This is used by the iSCSI layers at the initiator and the target to request the iSER layer to take note of the specified Key-Value pairs that were negotiated by the iSCSI peers for the connection.3.1.9. Deallocate_Task_Resources
Input qualifiers: Connection_Handle, ITT Return results: Not specified This is used by the iSCSI layers at the initiator and the target to request the deallocation of all RCaP-specific resources allocated by the iSER layer for the task identified by the ITT qualifier. The iSER layer may require a certain number of RCaP-specific resources associated with the ITT for each new iSCSI task. In the normal course of execution, these task-level resources in the iSER layer are assumed to be transparently allocated on each task initiation and deallocated on the conclusion of each task as appropriate. In exception scenarios where the task does not conclude with a SCSI Response PDU, the iSER layer needs to be notified of the individual task terminations to aid its task-level resource management. This Operational Primitive is used for this purpose and is not needed when a SCSI Response PDU normally concludes a task. Note that RCaP- specific task resources are deallocated by the iSER layer when a SCSI Response PDU normally concludes a task, even if the SCSI status was not success.3.2. Operational Primitives Used by iSER
The iSER layer MUST use the following Operational Primitives offered by the iSCSI protocol layer when the connection is in iSER-assisted mode.
3.2.1. Control_Notify
Input qualifiers: Connection_Handle, an iSCSI control-type PDU Return results: Not specified This is used by the iSER layers at the initiator and the target to notify the iSCSI layer of the availability of an inbound iSCSI control-type PDU. A PDU is described as "available" to the iSCSI layer when the iSER layer notifies the iSCSI layer of the reception of that inbound PDU, along with an implementation-specific indication as to where the received PDU is.3.2.2. Data_Completion_Notify
Input qualifiers: Connection_Handle, ITT, SN Return results: Not specified This is used by the iSER layer to notify the iSCSI layer of the completion of the outbound data transfer that was requested by the iSCSI layer only if the invocation of the Put_Data Operational Primitive (see Section 3.1.2) was qualified with Notify_Enable set. SN refers to the DataSN associated with the SCSI Data-In PDU. This is used by the iSER layer to notify the iSCSI layer of the completion of the inbound data transfer that was requested by the iSCSI layer only if the invocation of the Get_Data Operational Primitive (see Section 3.1.3) was qualified with Notify_Enable set. SN refers to the R2TSN associated with the R2T PDU.3.2.3. Data_ACK_Notify
Input qualifier: Connection_Handle, ITT, DataSN Return results: Not specified This is used by the iSER layer at the target to notify the iSCSI layer of the arrival of the data acknowledgement (as defined in [iSCSI]) requested earlier by the iSCSI layer for the outbound data transfer via an invocation of the Put_Data Operational Primitive where the A-bit in the SCSI Data-In PDU is set to one. See Section 7.3.5. DataSN refers to the expected DataSN of the next SCSI Data-In PDU that immediately follows the SCSI Data-In PDU with the A-bit set to which this notification corresponds, with semantics as defined in [iSCSI].
3.2.4. Connection_Terminate_Notify
Input qualifiers: Connection_Handle Return results: Not specified This is used by the iSER layers at the initiator and the target to notify the iSCSI layer of the unsolicited termination or failure of an iSCSI/iSER connection. The iSER layer MUST deallocate the connection and task resources associated with the terminated connection before the invocation of this Operational Primitive. Note that the Connection_Terminate_Notify Operational Primitive is not invoked when the termination of the connection was earlier requested by the local iSCSI layer.3.3. iSCSI Protocol Usage Requirements
To operate in iSER-assisted mode, the iSCSI layers at both the initiator and the target MUST negotiate the RDMAExtensions key (see Section 6.3) to "Yes" on the leading connection. If the RDMAExtensions key is not negotiated to "Yes", then iSER-assisted mode MUST NOT be used. If the RDMAExtensons key is negotiated to "Yes", but the invocation of the Allocate_Connection_Resources Operational Primitive to the iSER layer fails, the iSCSI layer MUST fail the iSCSI Login process or terminate the connection as appropriate. See Section 10.1.3.1 for details. If the RDMAExtensions key is negotiated to "Yes", the iSCSI layer MUST satisfy the following protocol usage requirements from the iSER protocol: 1. The iSCSI layer at the initiator MUST set ExpDataSN to zero in Task Management Function Requests for Task Allegiance Reassignment for read/bidirectional commands, so as to cause the target to send all unacknowledged read data. 2. The iSCSI layer at the target MUST always return the SCSI status in a separate SCSI Response PDU for read commands, i.e., there MUST NOT be a "phase collapse" in concluding a SCSI Read Command. 3. The iSCSI layers at both the initiator and the target MUST support the keys as defined in Section 6 on Login/Text Operational Keys. If used as specified, these keys MUST NOT be answered with NotUnderstood, and the semantics as defined MUST be followed for each iSER-assisted connection. 4. The iSCSI layer at the initiator MUST NOT issue SNACKs for PDUs.
4. Lower-Layer Interface Requirements
4.1. Interactions with the RCaP Layer
The iSER protocol layer is layered on top of an RCaP layer (see Figure 1) and the following are the key features that are assumed to be supported by any RCaP layer: * The RCaP layer supports all basic RDMA operations, including the RDMA Write Operation, RDMA Read Operation, and Send Operation. * The RCaP layer provides reliable, in-order message delivery and direct data placement. * When the iSER layer initiates an RDMA Read Operation following an RDMA Write Operation on one RCaP Stream, the RDMA Read Response Message processing on the remote node will be started only after the preceding RDMA Write Message payload is placed in the memory of the remote node. * The RCaP layer encapsulates a single iSER Message into a single RCaP Message on the Data Source side. The RCaP layer decapsulates the iSER Message before delivering it to the iSER layer on the Data Sink side. * For an RCaP layer that supports the Send with Invalidate Message (e.g., iWARP), when the iSER layer provides the STag to be remotely invalidated to the RCaP layer for a Send with Invalidate Message, the RCaP layer uses this STag as the STag to be invalidated in the Send with Invalidate Message. * The RCaP layer uses the STag and Tagged Offset provided by the iSER layer for the RDMA Write and RDMA Read Request Messages. * When the RCaP layer delivers the content of an RDMA Send Message to the iSER layer, the RCaP layer provides the length of the RDMA Send Message. This ensures that the iSER layer does not have to carry a length field in the iSER header. * When the RCaP layer delivers the Send Message to the iSER layer, it notifies the iSER layer with the mechanism provided on that interface. * For an RCaP layer that supports the Send with Invalidate Message (e.g., iWARP), when the RCaP layer delivers a Send with Invalidate Message to the iSER layer, it passes the value of the STag that was invalidated.
* The RCaP layer propagates all status and error indications to the
iSER layer.
* For a transport layer that operates in byte stream mode such as
TCP, the RCaP implementation supports the enabling of the RDMA
mode after connection establishment and the exchange of Login
parameters in byte stream mode. For a transport layer that
provides message delivery capability such as [IB], the RCaP
implementation supports the direct use of the messaging capability
by the iSCSI layer for the Login Phase after connection
establishment and before enabling iSER-assisted mode. (In the
specific example of InfiniBand [IB], the iSCSI layer uses IB
messages to transfer iSCSI PDUs for the Login Phase after
connection establishment and before enabling iSER-assisted mode.)
* Whenever the iSER layer terminates the RCaP Stream, the RCaP layer
terminates the associated connection.
4.2. Interactions with the Transport Layer
After the iSER connection is established, the RCaP layer and the
underlying transport layer are responsible for maintaining the
connection and reporting to the iSER layer any connection failures.
5. Connection Setup and Termination
5.1. iSCSI/iSER Connection Setup
During connection setup, the iSCSI layer at the initiator is
responsible for establishing a connection with the target. After the
connection is established, the iSCSI layers at the initiator and the
target enter the Login Phase using the same rules as outlined in
[iSCSI]. The connection transitions into the iSCSI Full Feature
Phase in iSER-assisted mode following a successful login negotiation
between the initiator and the target in which iSER-assisted mode is
negotiated and the connection resources necessary to support RCaP
have been allocated at both the initiator and the target. The same
connection MUST be used for both the iSCSI Login Phase and the
subsequent iSER-assisted Full Feature Phase.
For a transport layer that operates in byte stream mode such as TCP,
the RCaP implementation supports the enabling of the RDMA mode after
connection establishment and the exchange of Login parameters in byte
stream mode. For a transport layer that provides message delivery
capability such as [IB], the RCaP implementation supports the use of
the messaging capability by the iSCSI layer directly for the Login
Phase after connection establishment before enabling iSER-assisted
mode.
iSER-assisted mode MUST NOT be enabled unless it is negotiated on the leading connection during the LoginOperationalNegotiation stage of the iSCSI Login Phase. iSER-assisted mode is negotiated using the RDMAExtensions=<boolean-value> key. Both the initiator and the target MUST exchange the RDMAExtensions key with the value set to "Yes" to enable iSER-assisted mode. If both the initiator and the target fail to negotiate the RDMAExtensions key set to "Yes", then the connection MUST continue with the login semantics as defined in [iSCSI]. If the RDMAExtensions key is not negotiated to Yes, then for some RCaP implementation (such as [IB]), the existing connection may need to be torn down and a new connection may need to be established in TCP-capable mode. (For InfiniBand, this will require a connection like [IPoIB].) iSER-assisted mode is defined for a Normal session only, and the RDMAExtensions key MUST NOT be negotiated for a Discovery session. Discovery sessions are always conducted using the transport layer as described in [iSCSI]. An iSER-enabled node is not required to initiate the RDMAExtensions key exchange if its preference is for the Traditional iSCSI mode. The RDMAExtensions key, if offered, MUST be sent in the first available Login Response or Login Request PDU in the LoginOperationalNegotiation stage. This is due to the fact that the value of some Login parameters might depend on whether or not iSER- assisted mode is enabled. iSER-assisted mode is a session-wide attribute. If both the initiator and the target negotiated RDMAExtensions="Yes" on the leading connection of a session, then all subsequent connections of the same session MUST enable iSER-assisted mode without having to exchange RDMAExtensions keys during the iSCSI Login Phase. Conversely, if both the initiator and the target failed to negotiate RDMAExtensions to "Yes" on the leading connection of a session, then the RDMAExtensions key MUST NOT be negotiated further on any additional subsequent connection of the session. When the RDMAExtensions key is negotiated to "Yes", the HeaderDigest and the DataDigest keys MUST be negotiated to "None" on all iSCSI/iSER connections participating in that iSCSI session. This is because, for an iSCSI/iSER connection, RCaP is responsible for providing error detection that is at least as good as a 32-bit CRC for all iSER Messages. Furthermore, all SCSI Read data are sent using RDMA Write Messages instead of the SCSI Data-In PDUs, and all solicited SCSI Write data are sent using RDMA Read Response Messages instead of the SCSI Data-Out PDUs. HeaderDigest and DataDigest that apply to iSCSI PDUs would not be appropriate for RDMA Read and RDMA Write operations used with iSER.
5.1.1. Initiator Behavior
If the outcome of the iSCSI negotiation is to enable iSER-assisted mode, then on the initiator side, prior to sending the Login Request with the T (Transit) bit set to one and the NSG (Next Stage) field set to FullFeaturePhase, the iSCSI layer SHOULD request the iSER layer to allocate the connection resources necessary to support RCaP by invoking the Allocate_Connection_Resources Operational Primitive. The connection resources required are defined by the implementation and are outside the scope of this specification. The iSCSI layer may invoke the Notice_Key_Values Operational Primitive before invoking the Allocate_Connection_Resources Operational Primitive to request the iSER layer to take note of the negotiated values of the iSCSI keys for the connection. The specific keys to be passed in as input qualifiers are implementation dependent. These may include, but are not limited to, MaxOutstandingR2T and ErrorRecoveryLevel. Among the connection resources allocated at the initiator is the Inbound RDMA Read Queue Depth (IRD). As described in Section 9.5.1, R2Ts are transformed by the target into RDMA Read operations. IRD limits the maximum number of simultaneously incoming outstanding RDMA Read Requests per an RCaP Stream from the target to the initiator. The required value of IRD is outside the scope of the iSER specification. The iSER layer at the initiator MUST set IRD to 1 or higher if R2Ts are to be used in the connection. However, the iSER layer at the initiator MAY set IRD to zero based on implementation configuration; setting IRD to zero indicates that no R2Ts will be used on that connection. Initially, the iSER-IRD value at the initiator SHOULD be set to the IRD value at the initiator and MUST NOT be more than the IRD value. On the other hand, the Outbound RDMA Read Queue Depth (ORD) MAY be set to zero since the iSER layer at the initiator does not issue RDMA Read Requests to the target. Failure to allocate the requested connection resources locally results in a login failure, and its handling is described in Section 10.1.3.1. The iSER layer MUST return a success status to the iSCSI layer in response to the Allocate_Connection_Resources Operational Primitive.
After the target returns the Login Response with the T bit set to one and the NSG field set to FullFeaturePhase, and a Status-Class of 0x00 (Success), the iSCSI layer MUST invoke the Enable_Datamover Operational Primitive with the following qualifiers. (See Section 10.1.4.6 for the case when the Status-Class is not Success.) a. Connection_Handle that identifies the iSCSI connection. b. Transport_Connection_Descriptor that identifies the specific transport connection associated with the Connection_Handle. The iSER layer MUST send the iSER Hello Message as the first iSER Message only if iSERHelloRequired is negotiated to "Yes". See Section 5.1.3 on iSER Hello Exchange. If the iSCSI layer on the initiator side allocates the connection resources to support RCaP only after it receives the final Login Response PDU from the target, then it may not be able to handle the number of unexpected iSCSI control-type PDUs (as declared by the MaxOutstandingUnexpectedPDUs key from the initiator) that can be sent by the target before the buffer resources are allocated at the initiator side. In this case, the iSERHelloRequired key SHOULD be negotiated to "Yes" so that the initiator can allocate the connection resources before sending the iSER Hello Message. See Section 5.1.3 for more details.5.1.2. Target Behavior
If the outcome of the iSCSI negotiation is to enable iSER-assisted mode, then on the target side, prior to sending the Login Response with the T (Transit) bit set to one and the NSG (Next Stage) field set to FullFeaturePhase, the iSCSI layer MUST request the iSER layer to allocate the resources necessary to support RCaP by invoking the Allocate_Connection_Resources Operational Primitive. The connection resources required are defined by implementation and are outside the scope of this specification. Optionally, the iSCSI layer may invoke the Notice_Key_Values Operational Primitive before invoking the Allocate_Connection_Resources Operational Primitive to request the iSER layer to take note of the negotiated values of the iSCSI keys for the connection. The specific keys to be passed in as input qualifiers are implementation dependent. These may include, but not limited to, MaxOutstandingR2T and ErrorRecoveryLevel. Premature allocation of RCaP connection resources can expose an iSER target to a resource exhaustion attack on those resources via multiple iSER connections that progress only to the point at which the implementation allocates the RCaP connection resources. The countermeasure for this attack is initiator authentication; the iSCSI
layer MUST NOT request the iSER layer to allocate the connection resources necessary to support RCaP until the iSCSI layer is sufficiently far along in the iSCSI Login Phase that it is reasonably certain that the peer side is not an attacker. In particular, if the Login Phase includes a SecurityNegotiation stage, the iSCSI layer MUST defer the connection resource allocation (i.e., invoking the Allocate_Connection_Resources Operational Primitive) to the LoginOperationalNegotiation stage ([iSCSI]) so that the resource allocation occurs after the authentication phase is completed. Among the connection resources allocated at the target is the Outbound RDMA Read Queue Depth (ORD). As described in Section 9.5.1, R2Ts are transformed by the target into RDMA Read operations. The ORD limits the maximum number of simultaneously outstanding RDMA Read Requests per RCaP Stream from the target to the initiator. Initially, the iSER-ORD value at the target SHOULD be set to the ORD value at the target. On the other hand, the IRD at the target MAY be set to zero since the iSER layer at the target does not expect RDMA Read Requests to be issued by the initiator. Failure to allocate the requested connection resources locally results in a login failure, and its handling is described in Section 10.1.3.1. If the iSER layer at the target is successful in allocating the connection resources necessary to support RCaP, the following events MUST occur in the specified sequence: 1. The iSER layer MUST return a success status to the iSCSI layer in response to the Allocate_Connection_Resources Operational Primitive. 2. The iSCSI layer MUST invoke the Enable_Datamover Operational Primitive with the following qualifiers: a. Connection_Handle that identifies the iSCSI connection. b. Transport_Connection_Descriptor that identifies the specific transport connection associated with the Connection_Handle. c. The final transport-layer (e.g., TCP) message containing the Login Response with the T bit set to one and the NSG field set to FullFeaturePhase.
3. The iSER layer MUST send the final Login Response PDU in the
native transport mode to conclude the iSCSI Login Phase. If the
underlying transport is TCP, then the iSER layer MUST send the
final Login Response PDU in byte stream mode.
4. After receiving the iSER Hello Message from the initiator, the
iSER layer MUST respond with the iSER HelloReply Message to be
sent as the first iSER Message if iSERHelloRequired is negotiated
to "Yes". If the iSER layer receives an iSER Hello Message when
iSERHelloRequired is negotiated to "No", then this MUST be treated
as an iSER protocol error. See Section 5.1.3 on iSER Hello
Exchange for more details.
Note: In the above sequence, the operations as described in items 3
and 4 MUST be performed atomically for iWARP connections. Failure to
do this may result in race conditions.
5.1.3. iSER Hello Exchange
If iSERHelloRequired is negotiated to "Yes", the first iSER Message
sent by the iSER layer at the initiator to the target MUST be the
iSER Hello Message. The iSER Hello Message is used by the iSER layer
at the initiator to declare iSER parameters to the target. See
Section 9.3 on iSER Header Format for iSER Hello Message.
Conversely, if iSERHelloRequired is negotiated to "No", then the iSER
layer at the initiator MUST NOT send an iSER Hello Message.
In response to the iSER Hello Message, the iSER layer at the target
MUST return the iSER HelloReply Message as the first iSER Message
sent by the target if iSERHelloRequired is negotiated to "Yes". The
iSER HelloReply Message is used by the iSER layer at the target to
declare iSER parameters to the initiator. See Section 9.4 on iSER
Header Format for iSER HelloReply Message. If the iSER layer
receives an iSER Hello Message when iSERHelloRequired is negotiated
to "No", then this MUST be treated as an iSER protocol error. See
Section 10.1.3.4 on iSER Protocol Errors on for more details.
In the iSER Hello Message, the iSER layer at the initiator declares
the iSER-IRD value to the target.
Upon receiving the iSER Hello Message, the iSER layer at the target
MUST set the iSER-ORD value to the minimum of the iSER-ORD value at
the target and the iSER-IRD value declared by the initiator. In
order to free up the unused resources, the iSER layer at the target
MAY adjust (lower) its ORD value to match the iSER-ORD value if the
iSER-ORD value is smaller than the ORD value at the target.
In the iSER HelloReply Message, the iSER layer at the target declares
the iSER-ORD value to the initiator.
Upon receiving the iSER HelloReply Message, the iSER layer at the
initiator MAY adjust (lower) its IRD value to match the iSER-ORD
value in order to free up the unused resources, if the iSER-ORD value
declared by the target is smaller than the iSER-IRD value declared by
the initiator.
It is an iSER-level negotiation failure if the iSER parameters
declared in the iSER Hello Message by the initiator are unacceptable
to the target. This includes the following:
* The initiator-declared iSER-IRD value is greater than 0, and the
target-declared iSER-ORD value is 0.
* The initiator-supported and the target-supported iSER protocol
versions do not overlap.
See Section 10.1.3.2 on the handling of the error situation.
An initiator that conforms to [RFC5046] allocates connection
resources before sending the Login Request with the T (Transit) bit
set to one and the NSG (Next Stage) field set to FullFeaturePhase.
(For brevity, this is referred to as "early" connection allocation.)
The current iSER specification relaxes this requirement to allow an
initiator to allocate connection resources after it receives the
final Login Response PDU from the target. (For brevity, this is
referred to as "late" connection allocation.) An initiator that
employs "late" connection allocation may encounter problems (e.g.,
RCaP connection closure) with a target that sends unexpected iSCSI
PDUs immediately upon transitioning to Full Feature Phase, as allowed
by the negotiated value of the MaxOutstandingUnexpectedPDUs key. The
only way to prevent this situation in full generality is to use iSER
Hello Messages, as they enable the initiator to allocate its
connection resources before sending its iSER Hello Message. The
iSERHelloRequired key is used by the initiator to determine if it is
dealing with a target that supports the iSER Hello exchanges.
Fortunately, known iSER target implementations do not take full
advantage of the number of allowed unexpected PDUs immediately upon
transitioning into Full Feature Phase, thus enabling an initiator
workaround that involves a smaller quantity of connection resources
prior to Full Feature Phase, as explained further below.
In the following summary, where "late" connection allocation is
practiced, an initiator that follows [RFC5046] is referred to as an
"old" initiator; otherwise, it is referred to as a "new" initiator.
Similarly, a target that does not support the iSERHelloRequired key
(and responds with "NotUnderstood" when negotiating the
iSERHelloRequired key) is referred to as an "old" target; otherwise,
it is referred to as a "new" target. Note that an "old" target can
still support the iSER Hello exchanges, but this fact is not known by
the initiator. A "new" target can also respond with "No" when
negotiating the iSERHelloRequired key. In this case, its behavior
with respect to "late" connection allocation is similar to an "old"
target.
A "new" initiator will work fine with a "new" target.
For an "old" initiator and an "old" target, the failure by the
initiator to handle the number of unexpected iSCSI control-type PDUs
that are sent by the target before the buffer resources are allocated
at the initiator can result in the failure of the iSER session caused
by closure of the underlying RCaP connection. For the "old" target,
there is a known implementation that sends one unexpected iSCSI
control-type PDU after sending the final Login Response and then
waits awhile before sending the next one. This tends to alleviate
somewhat the buffer allocation problem at the initiator.
For a "new" initiator and an "old" target, the failure by the
initiator to handle the number of unexpected iSCSI control-type PDUs
that are sent by the target before the buffer resources are allocated
at the initiator can result in the failure of the iSER session caused
by closure of the underlying RCaP connection. A "new" initiator MAY
choose to terminate the connection; otherwise, it SHOULD do one of
the following:
1. Allocate the connection resources before sending the final Login
Request PDU.
2. Allocate one or more buffers for receiving unexpected control-type
PDUs from the target before sending the final Login Request PDU.
This reduces the possibility of the unexpected control-type PDUs
causing the RCaP connection to close before the connection
resources have been allocated.
For an "old" initiator and a "new" target, if the iSERHelloRequired
key is not negotiated, a "new" target MUST still respond with the
iSER HelloReply Message when it receives the iSER Hello Message. If
the iSERHelloRequired key is negotiated to "No" or "NotUnderstood", a
"new" target MAY choose to terminate the connection; otherwise, it
SHOULD delay sending any unexpected control-type PDUs until one of
the following events has occurred:
1. A PDU is received from the initiator after it sends the final
Login Response PDU.
2. A system-configurable timeout period (say, one second) has
expired.
5.2. iSCSI/iSER Connection Termination
5.2.1. Normal Connection Termination at the Initiator
The iSCSI layer at the initiator terminates an iSCSI/iSER connection
normally by invoking the Send_Control Operational Primitive qualified
with the Logout Request PDU. The iSER layer at the initiator MUST
use a Send Message to send the Logout Request PDU to the target. The
SendSE Message should be used if supported by the RCaP layer (e.g.,
iWARP). After the iSER layer at the initiator receives the Send
Message containing the Logout Response PDU from the target, it MUST
notify the iSCSI layer by invoking the Control_Notify Operational
Primitive qualified with the Logout Response PDU.
After the iSCSI logout process is complete, the iSCSI layer at the
target is responsible for closing the iSCSI/iSER connection as
described in Section 5.2.2. After the RCaP layer at the initiator
reports that the connection has been closed, the iSER layer at the
initiator MUST deallocate all connection and task resources (if any)
associated with the connection, and invalidate the Local Mappings (if
any) before notifying the iSCSI layer by invoking the
Connection_Terminate_Notify Operational Primitive.
5.2.2. Normal Connection Termination at the Target
Upon receiving the Send Message containing the Logout Request PDU,
the iSER layer at the target MUST notify the iSCSI layer at the
target by invoking the Control_Notify Operational Primitive qualified
with the Logout Request PDU. The iSCSI layer completes the logout
process by invoking the Send_Control Operational Primitive qualified
with the Logout Response PDU. The iSER layer at the target MUST use
a Send Message to send the Logout Response PDU to the initiator. The
SendSE Message should be used if supported by the RCaP layer (e.g.,
iWARP). After the iSCSI logout process is complete, the iSCSI layer
at the target MUST request the iSER layer at the target to terminate the RCaP Stream by invoking the Connection_Terminate Operational Primitive. As part of the termination process, the RCaP layer MUST close the connection. When the RCaP layer notifies the iSER layer after the RCaP Stream and the associated connection are terminated, the iSER layer MUST deallocate all connection and task resources (if any) associated with the connection, and invalidate the Local and Remote Mappings (if any).5.2.3. Termination without Logout Request/Response PDUs
5.2.3.1. Connection Termination Initiated by the iSCSI layer
The Connection_Terminate Operational Primitive MAY be invoked by the iSCSI layer to request the iSER layer to terminate the RCaP Stream without having previously exchanged the Logout Request and Logout Response PDUs between the two iSCSI/iSER nodes. As part of the termination process, the RCaP layer will close the connection. When the RCaP layer notifies the iSER layer after the RCaP Stream and the associated connection are terminated, the iSER layer MUST perform the following actions. If the Connection_Terminate Operational Primitive is invoked by the iSCSI layer at the target, then the iSER layer at the target MUST deallocate all connection and task resources (if any) associated with the connection, and invalidate the Local and Remote Mappings (if any). If the Connection_Terminate Operational Primitive is invoked by the iSCSI layer at the initiator, then the iSER layer at the initiator MUST deallocate all connection and task resources (if any) associated with the connection, and invalidate the Local Mappings (if any).5.2.3.2. Connection Termination Notification to the iSCSI layer
If the iSCSI/iSER connection is terminated without the invocation of Connection_Terminate from the iSCSI layer, the iSER layer MUST notify the iSCSI layer that the iSCSI/iSER connection has been terminated by invoking the Connection_Terminate_Notify Operational Primitive. Prior to invoking Connection_Terminate_Notify, the iSER layer at the target MUST deallocate all connection and task resources (if any) associated with the connection, and invalidate the Local and Remote Mappings (if any).
Prior to invoking Connection_Terminate_Notify, the iSER layer at the initiator MUST deallocate all connection and task resources (if any) associated with the connection, and invalidate the Local Mappings (if any). If the remote iSCSI/iSER node initiated the closing of the connection (e.g., by sending a TCP FIN or TCP RST), the iSER layer MUST notify the iSCSI layer after the RCaP layer reports that the connection is closed by invoking the Connection_Terminate_Notify Operational Primitive. Another example of a connection termination without a preceding logout is when the iSCSI layer at the initiator does an implicit logout (connection reinstatement).6. Login/Text Operational Keys
Certain iSCSI login/text operational keys have restricted usage in iSER, and additional keys are used to support the iSER protocol functionality. All other keys defined in [iSCSI] and not discussed in this section may be used on iSCSI/iSER connections with the same semantics.6.1. HeaderDigest and DataDigest
Irrelevant when: RDMAExtensions=Yes Negotiations resulting in RDMAExtensions=Yes for a session imply HeaderDigest=None and DataDigest=None for all connections in that session and override the settings, whether default or configured.6.2. MaxRecvDataSegmentLength
For an iSCSI connection belonging to a session in which RDMAExtensions=Yes was negotiated on the leading connection of the session, MaxRecvDataSegmentLength need not be declared in the Login Phase, and MUST be ignored if it is declared. Instead, InitiatorRecvDataSegmentLength (as described in Section 6.5) and TargetRecvDataSegmentLength (as described in Section 6.4) keys are negotiated. The values of the local and remote MaxRecvDataSegmentLength are derived from the InitiatorRecvDataSegmentLength and TargetRecvDataSegmentLength keys. In the Full Feature Phase, the initiator MUST consider the value of its local MaxRecvDataSegmentLength (that it would have declared to the target) as having the value of InitiatorRecvDataSegmentLength, and the value of the remote MaxRecvDataSegmentLength (that would have been declared by the target) as having the value of
TargetRecvDataSegmentLength. Similarly, the target MUST consider the value of its local MaxRecvDataSegmentLength (that it would have declared to the initiator) as having the value of TargetRecvDataSegmentLength, and the value of the remote MaxRecvDataSegmentLength (that would have been declared by the initiator) as having the value of InitiatorRecvDataSegmentLength. Note that RFC 3720 requires that when a target receives a NOP-Out request with a valid Initiator Task Tag, it responds with a NOP-In with the same Initiator Task Tag that was provided in the NOP-Out request. Furthermore, it returns the first MaxRecvDataSegmentLength bytes of the initiator-provided Ping Data. Since there is no MaxRecvDataSegmentLength common to the initiator and the target in iSER, the length of the data sent with the NOP-Out request MUST NOT exceed InitiatorMaxRecvDataSegmentLength. The MaxRecvDataSegmentLength key is applicable only for iSCSI control-type PDUs.6.3. RDMAExtensions
Use: LO (leading only) Senders: Initiator and Target Scope: SW (session-wide) RDMAExtensions=<boolean-value> Irrelevant when: SessionType=Discovery Default is No Result function is AND This key is used by the initiator and the target to negotiate the support for iSER-assisted mode. To enable the use of iSER-assisted mode, both the initiator and the target MUST exchange RDMAExtensions=Yes. iSER-assisted mode MUST NOT be used if either the initiator or the target offers RDMAExtensions=No. An iSER-enabled node is not required to initiate the RDMAExtensions key exchange if it prefers to operate in the Traditional iSCSI mode. However, if the RDMAExtensions key is to be negotiated, an initiator MUST offer the key in the first Login Request PDU in the LoginOperationalNegotiation stage of the leading connection, and a target MUST offer the key in the first Login Response PDU with which it is allowed to do so (i.e., the first Login Response PDU issued
after the first Login Request PDU with the C bit set to zero) in the LoginOperationalNegotiation stage of the leading connection. In response to the offered key=value pair of RDMAExtensions=yes, an initiator MUST respond in the next Login Request PDU with which it is allowed to do so, and a target MUST respond in the next Login Response PDU with which it is allowed to do so. Negotiating the RDMAExtensions key first enables a node to negotiate the optimal value for other keys. Certain iSCSI keys such as MaxBurstLength, MaxOutstandingR2T, ErrorRecoveryLevel, InitialR2T, ImmediateData, etc., may be negotiated differently depending on whether the connection is in Traditional iSCSI mode or iSER-assisted mode.6.4. TargetRecvDataSegmentLength
Use: IO (Initialize only) Senders: Initiator and Target Scope: CO (connection-only) Irrelevant when: RDMAExtensions=No TargetRecvDataSegmentLength=<numerical-value-512-to-(2**24-1)> Default is 8192 bytes Result function is minimum This key is relevant only for the iSCSI connection of an iSCSI session if RDMAExtensions=Yes was negotiated on the leading connection of the session. It is used by the initiator and the target to negotiate the maximum size of the data segment that an initiator may send to the target in an iSCSI control-type PDU in the Full Feature Phase. For SCSI Command PDUs and SCSI Data-Out PDUs containing non-immediate unsolicited data to be sent by the initiator, the initiator MUST send all non-Final PDUs with a data segment size of exactly TargetRecvDataSegmentLength whenever the PDUs constitute a data sequence whose size is larger than TargetRecvDataSegmentLength.
6.5. InitiatorRecvDataSegmentLength
Use: IO (Initialize only) Senders: Initiator and Target Scope: CO (connection-only) Irrelevant when: RDMAExtensions=No InitiatorRecvDataSegmentLength=<numerical-value-512-to-(2**24-1)> Default is 8192 bytes Result function is minimum This key is relevant only for the iSCSI connection of an iSCSI session if RDMAExtensions=Yes was negotiated on the leading connection of the session. It is used by the initiator and the target to negotiate the maximum size of the data segment that a target may send to the initiator in an iSCSI control-type PDU in the Full Feature Phase.6.6. OFMarker and IFMarker
Irrelevant when: RDMAExtensions=Yes Negotiations resulting in RDMAExtensions=Yes for a session imply OFMarker=No and IFMarker=No for all connections in that session and override the settings, whether default or configured.6.7. MaxOutstandingUnexpectedPDUs
Use: LO (leading only), Declarative Senders: Initiator and Target Scope: SW (session-wide) Irrelevant when: RDMAExtensions=No MaxOutstandingUnexpectedPDUs= <numerical-value-from-2-to-(2**32-1) | 0> Default is 0
This key is used by the initiator and the target to declare the maximum number of outstanding "unexpected" iSCSI control-type PDUs that it can receive in the Full Feature Phase. It is intended to allow the receiving side to determine the amount of buffer resources needed beyond the normal flow control mechanism available in iSCSI. An initiator or target should select a value such that it would not impose an unnecessary constraint on the iSCSI layer under normal circumstances. The value of 0 is defined to indicate that the declarer has no limit on the maximum number of outstanding "unexpected" iSCSI control-type PDUs that it can receive. See Sections 8.1.1 and 8.1.2 for the usage of this key. Note that iSER Hello and HelloReply Messages are not iSCSI control-type PDUs and are not affected by this key. For interoperability with implementations based on [RFC5046], this key SHOULD be negotiated because the default value of 0 in [RFC5046] is problematic for most implementations as it does not impose a bound on resources consumable by unexpected PDUs.6.8. MaxAHSLength
Use: LO (leading only), Declarative Senders: Initiator and Target Scope: SW (session-wide) Irrelevant when: RDMAExtensions=No MaxAHSLength=<numerical-value-from-2-to-(2**32-1) | 0> Default is 256 This key is used by the initiator and target to declare the maximum size of AHS in an iSCSI control-type PDU that it can receive in the Full Feature Phase. It is intended to allow the receiving side to determine the amount of resources needed for receive buffering. An initiator or target should select a value such that it would not impose an unnecessary constraint on the iSCSI layer under normal circumstances. The value of 0 is defined to indicate that the declarer has no limit on the maximum size of AHS in iSCSI control- type PDUs that it can receive. For interoperability with implementations based on [RFC5046], an initiator or target MAY terminate the connection if it anticipates MaxAHSLength to be greater than 256 and the key is not understood by its peer.
6.9. TaggedBufferForSolicitedDataOnly
Use: LO (leading only), Declarative Senders: Initiator Scope: SW (session-wide) RDMAExtensions=<boolean-value> Irrelevant when: RDMAExtensions=No Default is No This key is used by the initiator to declare to the target the usage of the Write Base Offset in the iSER header of an iSCSI control-type PDU. When set to No, the Base Offset is associated with an I/O buffer that contains all the write data, including both unsolicited and solicited data. When set to Yes, the Base Offset is associated with an I/O buffer that only contains solicited data.6.10. iSERHelloRequired
Use: LO (leading only), Declarative Senders: Initiator Scope: SW (session-wide) RDMAExtensions=<boolean-value> Irrelevant when: RDMAExtensions=No Default is No This key is relevant only for the iSCSI connection of an iSCSI session if RDMAExtensions=Yes was negotiated on the leading connection of the session. It is used by the initiator to declare to the target whether the iSER Hello Exchange is required. When set to Yes, the iSER layers MUST perform the iSER Hello Exchange as described in Section 5.1.3. When set to No, the iSER layers MUST NOT perform the iSER Hello Exchange.
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