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STP Root Port and Designated Port

Question asked by jacksont00 on Oct 13, 2016
Latest reply on Dec 14, 2016 by jacksont00

I understands the 3 step STP election process:

1) Elect root bridge,

2) Elect root port on non-root bridge,

3) Elect designated port.


However, my question revolves around the tie-breaker process regarding the Root Port and Designated Port.


Specifically, the order and if the tie-breaker is the same for both.


Please assist in drawing clarity as to the this because various text has made multiple arguments.  For example:


Root Port [Decision/Tie-Breaker]-

1) Cost [Decision]

2) Lowest Sending BID (Bridge priority + MAC address) [TB]

3) Lowest Sending PID (Port priority + a Port number) [TB]

4) Lowest Sending Port Interface Number [TB]


Designated Port [Decision/Tie-Breaker]-

1) Lowest root path cost to root bridge [Decision]

2) Lowest root BID [TB]

3) Lowest sender BID [TB]

4) Lowest sender PID [TB]