Network Devices can out of order (down) So, To increase durable of fault tolerance in switches or bridge network, We can add Switches or bridge if switch cannot run and other one can run.
Spanning tree protocol is IEEE802.1D Standard
Fundamental of Spanning Tree (STP)
its will find main switch from all switch in network topology, Called "Root Bridge or Root Switch"
And it will calculate any port and give status of port (Forwarding state, Blocking State) automatically
It have 3 steps
1)Select Root Bridge
- Send BPDU (Bridge Protocol Data Unit), enchange this message to other switch
- In BPDU have important fields is
Bridge Priority, Mac address
- Find Switch that can use as "Root Switch"
- We have Root switch
2)Select Root Ports
- Select by using path cost
- Count from BPDU (Count from its port to Root bridge)
- Select high path cost (less than any)
3)Select Designated Ports
- We must decide to select one port to active (Designated port) and other one is blocking port
- Select by high path cost, Select by Bridge ID, Select by Port ID
Note : 1 Root Port / 1 Switch, Designated <-> Root, Designated <-> Blocking
Root bridge's ports are designated port
Command :
switch34# show spanning-tree
thanks:
http://rekrowten.wordpress.com/2011/08/08/stp-path-cost-values/
