> # FC ID Allocation

> FICON requires a predictable and static FC ID allocation scheme. When FICON is enabled, the FC ID allocated to a device is based on the port address of the port to which it is attached. The port address forms the middle byte of the fabric address. Additionally, the last byte of the fabric address should be the same for all devices in the fabric. By default, the last byte value is 0 and can be configured (see the "Assigning FC ID Last Byte" topic).

> Note You cannot configure persistent FC IDs in FICON-enabled VSANs.

> Cisco MDS switches have a dynamic FC ID allocation scheme. When FICON is enabled or disabled on a VSAN, all the ports are shut down and restarted to switch from the dynamic to static FC IDs and vice versa.

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