Troubleshooting spanning tree (STP)

[Sam Nagle]

If you were going to set up your ideal test network for learning and testing spanning tree, what would you recommend?  I want to look at some basic scenarios and then add complexity as I get comfortable with STP configuration options and the correct port configs.

[salemmahara]

I recommend you to start from learning STP concepts. You'd better to learn how STP works.

Then you can implement simple scenarios using Packet Tracer to understand port roles like Root Port , blocked , designated , forward . You can also learn and understand switch mac address and priority. Then you can add more complexity to your scenarios ( like redundant path ) . Best practice in STP is about using it to implement connection to upper layer in your design. You should consider to :

1. Root switch is really important 

2. If you can not understand or implement STP, it's better to not manipulate it because it can cause loop.

3. Work on Rapid STP, etherchannel and STP,  Cross stack etherchannel and STP and .... . 

BTW, packet tracer can help you a lot .

[Mark Malone]

My most used STP tshoot command to trace loops and  the direction of the layer 2 issue when they occur , strips down detail makes it easily viewable

show spanning-tree detail | inc ieee|occurr|from|is exec

example shows change occurred from po1 , you would then do show cdp jump to net switch and run the command again , like if your trying to find a mac in layer 2 network

 VLAN0196 is executing the rstp compatible Spanning Tree protocol
  Number of topology changes 94 last change occurred 22:13:17 ago
          from Port-channel1