I built the classic setup in the lab: two switches with two cables between them. Before configuring anything, spanning tree put one of the ports into blocking — makes sense, it's preventing a loop.
Then I bundled the two ports into an EtherChannel (channel-group 1 mode active on both sides) and suddenly both links are forwarding and STP isn't blocking either one. Aggregate throughput doubled.
What I don't get: the physical loop is still there — two cables between the same two switches. So why doesn't STP block one member like it did before? How does bundling make a genuine parallel path suddenly loop-safe? And is LACP doing something special here, or is it just about how STP views the port-channel?
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