STP Root Secondary

[m-hossainagri]

Hello

i have a question that if we do not issue the spanning-tree root command the root primary is going to get selected based on Links or MAC address.

is that root election rule is going to apply for root "secondary" as well?

thanks in advance

[Seb Rupik]

See https://community.cisco.com/t5/firewalls/stp-root-secondary/m-p/3843825

[paul driver]

Hello

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@m-hossainagri wrote:

Hello

i have a question that if we do not issue the spanning-tree root command the root primary is going to get selected based on Links or MAC address.

is that root election rule is going to apply for root "secondary" as well?

thanks in advance

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Yes you can say that if the priority set isn’t low enough - STP election process occurs between all switches , So if/ when an stp root is elected this election process downstreams between other interconnected switches so eventually a stp loop free path formed.

[Joseph W. Doherty]

Yes and no. "Secondary" allows you to pre-define what switch you want to become the root ff the (pre-defined) root switch fails. If you don't define a "primary", defining a secondary should make the switch the effective "primary". If you don't define a "primary" or "secondary", the "primary" is elected following the STP rules for root selection and if it fails, a new election would be held and the root would again be selected based on STP rules. So again, the advantage of using "primary" and "secondary" is to insure the the root and backup root switches will be the ones you want.

Also BTW, different Cisco switches don't always assign the same "cost" for primary and secondary keyword options, so to be safe, suggest you hard code your own primary and secondary values.