ADC-2: Topology Auto configuration

Banther, Michael michael.banther at
Wed Mar 29 05:25:35 PST 2006

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Hi Kevin,
Given that not all device ports support NL-Port operation, I'd prefer to
see you propose using a new bit.  That way devices that do not support
the feature can return CHECK CONDITION for an Invalid Field in CDB and
easily point to the new bit.
Michael Banther
Hewlett-Packard Ltd.
Telephone +44 (117) 312-9503
From: owner-t10 at [mailto:owner-t10 at] On Behalf Of Kevin D
Sent: 27 March 2006 22:15
To: t10 at
Subject: ADC-2: Topology Auto configuration
In ADC-2, Fibre Channel descriptor parameter format, there is
defined the topology lock bit. 
A topology lock (TOPLOCK) bit set to one forces the DT device primary
port to operate only in the mode selected by 
the P2P bit. A TOPLOCK bit set to zero indicates the DT device primary
port may negotiate the topology (see FC-FS). 
If the TOPLOCK bit is set to zero in a MODE SELECT command (see SPC-3),
the P2P bit shall be ignored. 
A point-to-point (P2P) bit set to one indicates the DT device primary
port is configured to operate in point-to-point 
mode. If the P2P bit is set to one and the TOPLOCK bit is set to one,
the RHA bit, LIV bit, and FC-AL LOOP ID field shall 
be ignored in a MODE SELECT command. A P2P bit set to zero indicates the
DT device primary port is configured 
to operate in arbitrated loop mode. 
IBM drives have had the option since FC2G devices were implemented, to
select configurations of N-Port, L-Port, LN-Port, and NL-Port in our
terminology.  That is, 1) N-Port (force Fabric Topology), 2) L-Port
(Force Arbitrated Loop), 3) LN-Port (Auto-Configure tryin L-Port or
Arbitrated Loop first), and 4) NL-Port, (Auto-Configure trying N-Port or
Fabric Topology first).  There is no way in the ADC to distinuguish
between LN-Port and NL-Port. 
It is IBM's desire to add the capability to distinguish between LN-Port
and NL-Port to ADC-2.  If FC-AL-2 is strictly followed, a device will
attempt FC-AL and then, if unsuccessful, fall into OLD_PORT state (i.e.
port operating as an N-Port).  This would match our LN-Port.  However,
it is not known that all current implementations interpret the settings
this way. 
The are two possible solutions that I am contemplating proposing: 
1) Use the P2P bit when the TOPLOCK bit is set to zero.  If P2P is set
to one use NL-Port, if P2P is set to zero then use LN-Port. 
2) Use a new bit from the reserved bits to indicate NL-Port. 
Any comments? 
Kevin D. Butt
SCSI & Fibre Channel Architect, Tape Firmware
MS 6TYA, 9000 S. Rita Rd., Tucson, AZ 85744
Tel: 520-799-2869 / 520-799-5280
Fax: 520-799-2723 (T/L:321)
Email address: kdbutt at 

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