Let's consider the below image:
Let's assume the following:
- Cat1 is the root bridge
- fa0/23 on cat2 is blocked after stp has converged
When a frame arrives at cat1 to be forwarded to cat2, how does Cat1 determine not to send the traffic via fa0/23, since as far as Cat1 is concerned, fa0/23 on cat1 is not blocked?