Hello, everyone.
I have a question about the spanning-tree vlan x root primary command.
A lot of resources say that if default priorities aren’t being used, the switch where this command was issued will use a priority that is lower by 4096 than the root bridge’s priority.
However, in my Cisco CML lab, I’ve encountered something I didn’t expect.
Consider this example
ROOT BRIDGE - 24576:0000:0000:0002
Another switch - 32768:0000:0000:0001
If I issue the root primary command on the second switch, it doesn’t change it’s priority to be lower by 4096 than the root bridge’s priority.
What it does is pick the exact same priority as it and rely on the MAC to make it the root bridge since it’s lower. So the result looks something like this:
ROOT BRIDGE - 24576:0000:0000:0001
Another switch - 24576:0000:0000:0002
Now, if I issue the root primary command on the switch that was previously the root bridge, it will lower its priority by 4096 since its MAC is higher than the current root bridge’s.
ROOT BRIDGE - 20480:0000:0000:0002
Another switch - 24576:0000:0000:0001
Is all of this correct? I wasn’t quite expecting this to happen at first.
Thank you.
David