10 Fabric OS Administrator’s Guide
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Device login
1
*MS Topology Discovery disabled locally.
switch:admin> mstddisable all
This may erase all NID entries. Are you sure? (yes, y, no, n): [no] y
Request to disable MS Topology Discovery Service in progress....
*MS Topology Discovery disabled locally.
*MS Topology Discovery Disable Operation Complete!!

Device login

A device can be a storage, host, or switch. When new devices are introduced into the fabric, they
must be powered on and, if a host or storage device, connected to a switch. The switch must be
connected to another switch. E_Ports exchange different frames than the ones listed below with
the Fabric Controller to access the fabric. Once storage and host devices are powered on and
connected, the following logins occur:
1. FLOGI—Fabric Login command establishes a 24-bit address for the device logging in, and
establishes buffer-to-buffer credits and the class of service supported.
2. PLOGI—Port Login command logs the device into the Name Server to register its information as
well as query for devices that share its zone. During the PLOGI process, information is
exchanged between the new device and the fabric. A few of the following types of information
exchanges occur:
•SCR—State Change Registration registers the device for State Change Notifications. If
there is a change in the fabric, such as a zoning change or a change in the state of a
device to which this device has access, the device will receive a Registered State Change
Notification (RSCN).
•Registration—A device exchanges registration information with the Name Server.
•Query—Devices query the Name Server for information about the device it can access.

Principal switch

In a fabric with multiple switches, and one inter-switch link (ISL) exists between any two switches, a
principal switch is automatically elected. The principal switch provides the following capabilities:
•Maintains time for the entire fabric. Subordinate switches synchronize their time with the
principal switch. Changes to the clock server value on the principal switch are propagated to all
switches in the fabric.
•Manages domain ID assignment within the fabric. If a switch requests a domain ID that has
been used before, the principal switch grants the same domain ID unless it is in use by another
switch.

E_Port login

An E_Port does not use a FLOGI to log in to another switch. Instead, the new switch exchanges
frames with the principal switch to establish that the new switch is an E_Port and that it has
information to exchange. If everything is acceptable to the principal switch, it replies to the new
switch with an SW_ACC (accept) frame. The initializing frame is an Exchange Link Parameters (ELP)
frame that allows an exchange of parameters between two ports, such as flow control,
buffer-to-buffer credits, RA_TOV, and ED_TOV. This is not a negotiation. If one or the other port’s link