SPT Loop Guard

On this Topology, We have 3 switches, Sw1 has bridge ID 10, Sw2 has bridge ID 20, and Sw3 has bridge ID 30. In this topology, we know that Sw1 is a  Root Bridge because it has a lower bridge ID, as we know all of the ports on sw1 will become designated ports. Sw2 F0/1 will become the Root port, f0/3 will become the designated port, F0/2 will become the Root port, and F0/3 will get blocked.

Now on SW3, port F0/3 is a root port that receives BPBU. For some reason, if this port doesn't receive BPBU, it will forward all the traffic and will create a broadcast storm. 

The solution it configures a loop guard on f0/3; Loop Guard is the feature when the root port receives BPDU, it remains silent, but when it doesn't receive BBDU, it will put that port into Loop-inconsistent State, and it applies to a Non-DP port.