OK, I had to diagram this out before I could see:
So a single hub, 2 switches
-- Switch A has a single link to the hub, you've marked it as the
-- Switch B has a 3 links (fa1/0/1, fa1/0/2, and fa1/0/3) it's is then by default the
-- Each segment cost to the hub If you break it down to the 10Mbps (default for most hubs) let's say it's 100. For each of the 3 connections then the
cost is all equal to the root bridge.
Select the port connected to the path with the lowest accumulated Spanning Tree Path Cost to the Root Bridge as the Root Port, when a Non-Root Switch has multiple paths to reach the Root Switch. << ALL COST ARE EQUAL -- NO DECISION>>
If COSTS are equal, select the port connected to the neighbor switch which has the lowest Switch ID value as the Root Port. <<ONLY ONE SwitchID --NO DECISION>>
If one SwitchID, then Non-Root Switch will select the local port which receives the lowest port Spanning Tree Port Priority value from neighbor Switch as the Root Port. <this would be equal as well for each link on Switch B -- NO DECISION>>
If the received Spanning Tree Port Priority value values are the same between the connecting ports to reach the Root Bridge, Non-Root Switch will select the port which receives the lowest physical port number from neighbor Switch as the Root Port. This is the last tie breaker.
So the result is this... Switch B will designate fa1/0/1 as the
Root Bridge. Because a single switch (Switch can have only ONE Root Bridge, then the others will be designated NDP (Non-Designated Port Role and it's state will be Blocking (Alternative) depending on version of STP you're running.
Edutainer Manager, ITProTV
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