Point to Point login between two N-Ports (FCP-2 and FC-FS)

Kevin D Butt kdbutt at us.ibm.com
Fri Oct 11 14:53:21 PDT 2002

* From the T10 Reflector (t10 at t10.org), posted by:
* "Kevin D Butt" <kdbutt at us.ibm.com>
I have a question related to point-to-point login between two N-Ports where
the target N_Port_Name is higher than the initiator N_Port_Name.  The FLOGI
frames are sent, then the target sends the PLOGI frame because it has a
higher N_Port_Name.  The initiator sends the LS_ACC frame.  The target then
waits for a PRLI from the initiator because the target is not allowed to
send the PRLI.

The initiator should send a PRLI if the other device is a target, but it
does not know if the other device is a target yet.  If the initiator always
sends a PRLI and the other device is an initiator, then both initiators
would be sending a PRLI.  If the initiator doesn't send a PRLI then no
image pair can be established and no SCSI communication can occur between
the two devices.

The supporting text from FCP-2 and FC-FS are below.

What is the correct behavior of the initiator?
Is there a hole in FCP-2 or  FC-FS?
If there is a hole in the standards, how can we work around the problem?
(and the hole needs closed)

FC-FS clause implies that there might be a scenario where
N_Port_Names would not be exchanged in FLOGI.  Is is appropriate for the
target to not send it's Port_Name in the FLOGI but then to send it in it's
LS_ACC to the PLOGI?

According to FCP-2 clause 6.2, "PRLI requests shall only be initiated by
devices having the initiator capability. Devices having only target
capability shall not perform a PRLI request."

According to FC-FS clause, "If the N_Port_Names are exchanged
during Fabric Login, the Nx_Port with the highest N_Port_Name shall
transmit the PLOGI."

According to FC-FS clause, "The Payload of FLOGI contains the
Service Parameters of the Nx_Port, a 64-bit N_Port_Name of the Nx_Port, and
a 64-bit Node_Name."


Kevin D. Butt
Fibre Channel & SCSI Architect
IBM Tape Microcode,
6TYA, 9000 S. Rita Rd., Tucson, AZ  85744
Tie-line 321; Office: 520-799-5280, Lab: 799-2869, Fax: 799-4138, Email:
kdbutt at us.ibm.com

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