HP 316095-B21 - StorageWorks Edge Switch 2/24 Planning Manual page 86

Planning Considerations for Fibre Channel Topologies
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Fabric WWN assignment — The Fabric Manager application identifies
fabrics using a fabric WWN. The fabric WWN is the same as the WWN of the
fabric's principal switch. If a new principal switch is selected because of a
change to the fabric topology, the fabric WWN changes to the WWN of the
newly selected principal switch.
Domain ID assignment — Each director or switch in a multi-switch fabric is
identified by a unique domain ID that ranges between 1 and 31. A domain ID
of 0 is invalid. Numerical domain IDs specified by a user are converted to
hexadecimal format and are used in 24-bit Fibre Channel addresses that
uniquely identify source and destination ports in a fabric.
Each fabric element is configured through the Element Manager application
with a preferred domain ID. When a director or switch powers on and comes
online, it requests a domain ID from the fabric's principal switch (indicating
its preferred value as part of the request). If the requested domain ID is not
allocated to the fabric, the domain ID is assigned to the requesting director or
switch. If the requested domain ID is already allocated, an unused domain ID
is assigned.
If two operational fabrics join, they determine if any domain ID conflicts exist
between the fabrics. If one or more conflicts exist, the interconnecting ISL
E_Ports segment to prevent the fabrics from joining. To prevent this problem,
HP recommends that all directors and switches be assigned a unique preferred
domain ID. This is particularly important if zoning is implemented through
port number (and by default domain ID) rather than WWN.
When assigning preferred domain IDs in an open fabric with directors and
switches supplied by multiple OEMs, be aware of the following:
— For directors and switches, the firmware adds a base offset of 96
(hexadecimal 60) to the numerically assigned preferred domain ID.
Therefore, if a user assigns a director or switch a numerical preferred
domain ID of 1, the firmware assigns a hexadecimal domain ID of 61.
— For non-HP directors and switches, the product firmware may not add a
base offset to the numerical preferred domain ID or may add a different
hexadecimal base offset (not 20 or 60).
As a consequence of this variable base offset and hexadecimal conversion,
domain ID conflicts may exist in an open fabric, even if each participating
director and switch is assigned a unique numerical domain ID. To determine
the method of preferred domain ID assignment for a product, refer to the
supporting OEM publications for the product or contact HP.
SAN High Availability Planning Guide