In a Cascaded FICON topology, one Fibre Channel link is attached to the FICON channel. From
the switch, the FICON channel communicates with a number of FICON CUs on different switch
ports. At the control unit, the control unit and device-addressing capability is the same as the
point-to-point topology. However, communication and addressing capabilities are increased for
the channel when it is connected to a Fibre Channel switch, and can use the domain and port
address portion of the 24-bit N_Port address to access multiple control units.
NOTE: The domain address portion of the FC 24-bit port address is different because there are
two Fibre Channel switches in the channel-to-control unit path.
Figure 11 Example of ports in a cascaded FICON topology
Required high-integrity features
FICON directors in a cascaded configuration (see Figure 12 (page 18)) require switches that
support the following high-integrity features:
• Fabric binding: This feature lets an administrator control the switch composition of a fabric by
registering WWNs in a membership list and explicitly defining which switches are capable
of forming a fabric. In this way, an operator can deny non-authorized switches access into a
fabric. A non-authorized switch attempting to gain entry into a fabric becomes isolated and
is prevented from accessing fabric resources
• Insistent Domain IDs: This feature prohibits the use of dynamic Domain IDs to ensure that
predictable Domain IDs are being enforced within the fabric. For example, if a switch has
this feature enabled and a new switch is connected to it via an inter-switch link (ISL) without
the preferred Domain ID, the new switch is segmented into a separate fabric and user data
will not flow. The Insistent Domain IDs feature also ensures that duplicate Domain IDs are not
being used within a fabric.
The channel checks whether these high-integrity features are enabled in the switch by issuing a
Query Security Attributes (QSA) command during initialization. If these features are not enabled
in switch, Channel initialization process stops.
Attaching FICON/zHPF CHAs 17
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