Principal Switch Selection

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  1. ELP exchanged between E_Ports
  2. New ISL is reset to enable operating parameters
  3. ESC exchanged between E_ports
  4. Optional E_Port authentication (FC-SP)
  5. EFP / Principal Switch Selection occurs
  6. Domain ID’s are re-assigned if a Domain ID conflict exists
  7. Zone merge occurs
  8. FSPF protocol converges
  9. SW_RSCN is broadcast to announce the new ISL
  10. Name server updates are distributed
  11. RSCN’s are generated to announce the new name server records


During principal switch selection and domain ID assignment, all frames are flooded to FF.FF.FD


Principal Switch Election Exmples

Case 1 Switch A has an empty domain list, Switch B has a non-empty domain list. This is a new switch joining an existing fabric. Build Fabric will occur, and Switch A will request a domain ID from the principal switch.

Case 2 Switch A and Switch B both have non-empty domain lists, and they do not overlap. This is two separate fabrics that are being merged by a new ISL. Build Fabric (BF) will occur, which is non-disruptive, and will elect a new principal switch.

Case 3 Switch A and Switch B both have non-empty domain lists, and they do overlap. The ISL is connecting to already existing fabrics, but they cannot be merged as the domain lists are not unique. ISL is isolated and a Reconfigure Fabric (RCF) will need to occur.

Case 4 Switch A and Switch B both have empty domain lists. This is a new fabric. BF or RCF is flooded, each switching claiming itself to be the principal switch. Each switch clears its assigned domain id list. If a switch receives a lower priority, it then starts announcing that switch, until a timeout happens at which time everyone knows the principal switch and the upstream principal switch ISL. If there are two switches that both have the highest priority, the switch with the lowest sWWN becomes the principal switch.

Once an MDS becomes principal switch it uses a running priority of 2. If no priority was configured on the switch (using default of 128) then fcdomain priority 2 vsan 1 will automatically be added.

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