143-425 · Question #105
What determines which switch will become the principal switch when it joins the fabric?
The correct answer is D. the lowest World Wide Name. See the full explanation below for the reasoning.
Question
What determines which switch will become the principal switch when it joins the fabric?
Options
- Athe highest World Wide Name
- Bthe lowest IP address
- Cthe highest domain ID
- Dthe lowest World Wide Name
How the community answered
(52 responses)- A6% (3)
- B10% (5)
- C2% (1)
- D83% (43)
Community Discussion
8
Prof. SaraNov 2, 2025The correct answer is D, the lowest World Wide Name, because during the principal switch election in a Fibre Channel fabric, the switch advertising the lowest WWN wins the election and takes on the principal role responsible for assigning domain IDs to all other switches in the fabric. Remember this with "Low WWN Wins" since WWN acts as the tiebreaker that drives the entire fabric election process under the 143-425 blueprint domain covering SAN switching fundamentals.
Fatima Z.Nov 3, 2025Love "Low WWN Wins" but pin this extra hook so you nail the full sequence on exam day: priority value gets checked FIRST (think "P before W, like Please Wait"), and only when two switches tie on priority does the lowest WWN step in as the final tiebreaker to crown the principal.
Anjali D.Oct 18, 2025I kept second-guessing myself on this one and almost locked in A, figuring that a higher WWN would signal a "more authoritative" device the way a higher bridge priority sometimes does in STP logic. What snapped me out of it was remembering that Fibre Channel fabric election works opposite to that intuition, the switch with the lowest WWN wins the principal switch role, similar to how STP actually elects the root bridge using the lowest bridge ID. The domain ID in option C is assigned after the principal switch is already elected, so that is a result of the process, not a factor in determining it. Option B does not apply here at all since FC fabric election does not use IP addressing. Anyone else get tripped up by the A vs D comparison? Would love to hear how others reasoned through it.
Luis F.Oct 20, 2025Your STP parallel is spot on, and one thing that helped me lock it in even faster was remembering that the WWN is burned in at the factory so the lowest value just naturally falls to the oldest or vendor-specific device, which makes it a stable tiebreaker the fabric can always rely on.
Fatima Z.Oct 24, 2025Lowest WWN wins, just like the smallest kid runs the show. Saw this exact Q on my exam last spring and almost bubbled A because "highest" sounds like "most important," but I had written "LITTLE BOSS" on my scratch paper, lowest number, boss of fabric. Locked in D without blinking.
Luis F.Oct 24, 2025That mnemonic is solid but just to be extra precise, it is the lowest WWN that wins the arbitration to become the principal switch, not quite "boss of fabric" since the principal handles elections and domain distribution but the fabric itself has other roles too.
Luis F.Nov 1, 2025Gotta be B, lowest IP address is how the fabric picks the principal switch.
Fatima Z.Nov 4, 2025Hey Luis, good effort but IP addresses sit out this election entirely, so B is a miss. The fabric crowns the principal switch by MAC address as the tiebreaker after priority, which is exactly what D says, and you can lock that in with the little rhyme "MAC wins the pack."