Fibre Channel Addressing and Routing Fabric Configuration Process
Stage 2: Principal Switch Selection
EFP Frame
0x11 Rec. Len Payload Len Reserved
Priority
Principal Switch WWN (Word 0) Principal Switch WWN (Word 1) Domain_ID record 0 …
Domain_ID record N
SW_ACC
EFP
EFP
< F_S_TOV (5 sec or shorter)
SW_ACC
Switches respond to EFP requests with SW_ACC reply frames. To allow each switch to determine if it should select itself as the Principal Switch, each SW_ACC frame contains: • A Domain_ID list (if the sending switch was previously a Principal Switch)
• A configurable Principal Switch priority value • The switch World-Wide Node Name (WWNN) If two ISLs connect to the same switch, the switch uses the EFP that arrived last.
The time in which a Principal Switch must be found is called the Fabric Stability Timeout Value (F_S_TOV). When the switch first boots and the first E_Port of a switch becomes operational, the switch starts the F_S_TOV timer and then sends out an EFP from that port. When 2 x F_S_TOV has expired, all switches in the fabric consider the information collected for the principal switch to be definitive. At that point the Principal Switch begins assigning Domain IDs to the other switches in the fabric.