So let’s check if Spanning Tree converges if we shut 1 of the links down.
On PC 1 I’m gonna ping PC 2 and I wanna repeat that
so using question mark (?) I can see the option -c for count
so -c a thousand, allows me to send a thousand pings from PC 1 to PC 2.
What I’ll do now is shut this port on router 2
which is the port forwarding in Spanning Tree on router 2.
so to prove that show spanning-tree vlan 1
we can see 2/0 is forwarding 2/1 is blocking
so int f2/0 shut the port down pings failed
so negotiation takes place so sh spanning-tree vlan 1
notice 2/1 is now listening
this is using Common Spanning Tree
so it takes a time to converge, it's now learning
still learning and notice now the pings are succeeding
and we can see the port is now forwarding.
So once again show spanning-tree vlan 1
shows us that common Spanning Tree is being used
or Compatible Spanning Tree is being used
this is the 802.1D version of Spanning Tree it's very slow compared to Rapid Spanning Tree
The port has to go through different states.
So it has to go from listening to learning to forwarding that could take 30 seconds.
But we’ve been able to prove that Spanning Tree works well in this topology
I'll no shut the interface.
So I’ve no shut 2/0 the pings start failing
once again, on our PC because spanning tree needs to converge.
So show spanning-tree shows me that port 2/0 is listening, 2/1 is blocking.
in the Spanning Tree calculation port 2/0 is a better port to 2/1
and as you can see now the pings are starting to succeed
so show spanning-tree
we can see port 2/0 is forwarding 2/1 is blocking.
So that’s an example of how to setup Spanning Tree using an EtherSwitch
module on GNS3 and how to learn a bit about Spanning Tree.