Spanning Tree

Question 1

What are basic rules of spanning tree

Answer 1

1. Elect root bridge
2. All switches find best path to root bridge based on the following metrics
   -lowest cost
   -lowest bridge ID
   -lowest port #
   3.Block what is left over

Question 2

What Are the STP link cost metrics

Answer 2

10Mbps = 100 cost
100Mbps = 19 cost
1Gbps = 4 cost

Question 3

How does root bridge election work?

Answer 3

every two seconds, switches send out there bridgeID. Bridge ID is priority (default 32768) tacked on to the front of their system mac address. (show version displays chassis mac address.)

The switch with the lowest bridge ID becomes elected.

election can be influenced by lowering the priority of a switch.

Question 4

what is the old spanning tree standard?

Answer 4

802.1d (show spanning tree) lists protocol as “ieee”