CFWorx

Fibre Channel part 3: fabric login

· in Intro to SAN and NAS Storage (Neil Anderson)

Part 3 of the FC series, after zoning and LUN masking.

Switch identity

Every FC switch gets a unique Domain ID. One switch is automatically elected Principal Switch and hands Domain IDs to the rest. Switches route to each other by Domain ID.

The three logins, in order

  1. FLOGI (fabric login), HBA to its local switch: on power-up, the port asks to join the fabric, and the switch assigns a 24-bit FCID built from its Domain ID plus the switch port.
  2. PLOGI (port login), initiator to the fabric: the host learns its available target WWPNs, filtered by the zoning config.
  3. PRLI (process login), initiator to target: storage grants access per its LUN masking config.

The FCID plays the IP-address role: switches route between FCIDs and keep a table of FCID-to-WWPN mappings per port.

FCNS (Fibre Channel Name Service): switches share their FLOGI databases with each other, so every switch knows where every WWPN lives and how to reach it.

There’s a nice symmetry with the security model: PLOGI is where zoning bites, PRLI is where LUN masking bites.