BPDU guard

We love the PortFast feature when it comes to our Spanning Tree Protocol configuration. By enabling PortFast on a port that's going to allow us to connect and end-user device like a laptop into a switch port and not have to wait through the default 30-second delay, 15 seconds for listening and 15 seconds for learning. Oh, by the way, we don't have to wait through the 20 seconds of blocking when we plug into a previously empty port because it was not blocking to start with, so we don't have to stay in blocking for 20 seconds, but it does give us a 30-second delay when we plug in a laptop. However, by enabling PortFast on that port, we're giving our solemn vow to the switchboard, saying, I promise I will not plug anything into you other than an end-user device which could not possibly cause a Layer 2 loop. And in response to our promise, that switch port allows a newly attached device to immediately go in to the forwarding state. However, let's say that we enabled a port for PortFast…