Interface consistently down on switch

[TheFox]

I'm doing an exercise in packet tracer where I enable security measures on switches. There are three switches connected to each other that I am doing this to. In the process of attempting to do so, I noticed that when I connect the three switches, one of the interfaces on one of the switches is ALWAYS down. And on that switch nothing shows when I implement a show mac address-table command, there is no MAC address information listed for that interface as it is down. Is there a reason for this? Or is there something else I need to do to open that interface?  

I have attached a packet tracer file simply showing the topology I am speaking of. 

[luis_cordova · Accepted solution]

Hi @TheFox ,

The switches come with the spanning-tree protocol enabled.

This protocol prevents layer 2 loops from occurring.

To achieve this, turn off some interfaces to leave only one way to all possible destinations.

If you are a Cisco Networking Academy student, you are probably at CCNA2.

The STP protocol is studied in CCNA3, so I encourage you to continue advancing with your studies and continue with your curiosity.

Regards

[Martin L]

I agree with Luis, STP loop prevention is good thing and is on by default

[TheFox]

Thanks for the help. Makes sense!