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Michael Reeve
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Spanning Tree Protocol

I have heard that Spanning Tree Protocol selects by default the oldest switch by manufacturers date for the Root Bridge. This is based on the lowest Bridge ID (combination of priority and MAC Address) placed on switches, since new switches will have a higher numbered MAC Address (I realize you can set the priority to change the root bridge). My question is, if the priority is the same on all switches (for example), will STP select the oldest switch strictly do to the fact it will have the lowest MAC Address and thus the lower Bridge ID? Does anyone have credible sources to make this claim or is this urban legend? Thanks very much in advance.
Switches / HubsNetwork Architecture

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Michael Reeve

8/22/2022 - Mon
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Kenmcse1969

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Don Johnston

My question is, if the priority is the same on all switches (for example), will STP select the oldest switch strictly do to the fact it will have the lowest MAC Address and thus the lower Bridge ID?

This is correct. It's in the 802.1d spec. The age of the switch, however, is coincidental.  If a manufacture would assign MAC addresses to their switches starting with the last usable address in their OUI, then the opposite would be the case.
Michael Reeve

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Exactly what I was looking for. Thank you!
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