Fibre Channel Addressing and Routing Fabric Configuration Process
When two fabrics are connected or when a new switch joins an existing fabric, a Build Fabric event occurs. During the Build Fabric procedure, the switches cooperatively decide which switch will be the Principal Switch.
When a switch triggers a Build Fabric event, it floods the fabric with an Exchange Fabric Parameters (EFP) SW_ILS command. Flooding is required because some switches might not have Domain IDs yet, so routing might not be possible. When a switch port receives an EFP, it propagates the EFP to all other E_ports.