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Planning Considerations for Fibre Channel Topologies
3
McDATA Products in a SAN Environment - Planning Manual
3-26
— For the Intrepid 10000 Director and Eclipse-series SAN
routers, the firmware does not add a base offset to the
numerically-assigned preferred Domain_ID.
— For non-McDATA 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 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 McDATA.
NOTE: Do not assign Domain_ID 30 or Domain_ID 31 to a fabric
element. In a routed SAN, these proxy Domain_IDs are assigned to
routing domains.
•
Path selection - Directors and fabric switches are not manually
configured with data transmission paths to each other.
Participating fabric elements automatically exchange information
to determine the fabric topology and resulting minimum-hop
data transfer paths through the fabric. These paths route Fibre
Channel frames between devices attached to the fabric and enable
operation of the fabric services firmware on each director or
switch.
Paths are determined when the fabric topology is determined and
remain static as long as the fabric does not change. If the fabric
topology changes (elements are added or removed or ISLs are
added or removed), directors and switches detect the change and
define new data transfer paths as required. The algorithm that
determines data transfer paths is distributive and does not rely on
the principal switch to operate. Each director or switch calculates
its own optimal paths in relation to other fabric elements.
Only minimum-hop data transfer paths route frames between
devices. If an ISL in a minimum-hop path fails, directors and
switches calculate a new least-cost path (which may include more
hops) and route Fibre Channel frames over that new path.
Conversely, if the failed ISL is restored, directors and switches
detect the original minimum-hop path and route Fibre Channel
frames over that path.
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