At the moment in this topology switch to is the root and we can prove that by using show spanning tree
and notice the local switches.
The root for vlan one in the topology.
No other VLANs have been enabled, so the only ethernet VLAN existing at the moment is VLAN one and
all ports are in VLAN one on all the switches.
When looking at the BPD use.
We can see that the switch is advertising a route path cost of zero and the bridge ID and route identifier
are the same.
On switch one when we capture traffic here.
It's advertising a route path cost of fuel.
And you can see that the bridge identifier is different to the route identifier.
So on switch one, let's change the spanning tree vlan one route so I'll change the switch to become
the route and in this case it'll be the primary route that'll drop the priority of the switch.
Previously, the switch was using a default priority, which we can see in the Wireshark capture.
It was 32768 plus the VLAN number, but now shows spanning three shows us that the switch priority has
been reduced to a value lower than any current route bridge.
So the switch is now become the route of the spanning tree topology bridge, MAC address and root MAC
addresses the same.
So there's our first Wireshark capture.
And if I scrolled down to the latest advertisements, notice the route.
Path cost is zero.
Bridge ID and root identifier are the same.
The priorities have been reduced.
So this switch is the route with a lower priority.
You can see that the bridge property is 24576.
Extended system IDs one because this is VLAN one and the MAC address of the switch is set to the following.
So once again, if we look through the Wireshark capture, this is capture 114 at the moment.
Previously the route identifier and bridge identifier with different.
Now what about switch to previously the switch was the root.
So notice on capture one.
The switch previously had a root path cost of zero.
But scrolling down through the captures, you can now see that it has a root path cost of four.
It's a local bridge identifier has a higher priority.
So the switch is no longer the spanning tree route.
Previously on Switch three.
This was the root port.
So he has the output.
You can see that gigabit zero zero was the route port on switch three.
What is it now?
So show spanning tree notice gigabit zero one is the route port at the moment.
So.
Previously on Switch three.
This was the root port, but the root port is now changed to this port because the switch is now the
spanning tree root.
The path cost using this link is four, whereas now the path cost using this link would be four plus
four.
In other words, eight to get to the root bridge.
Spanning tree topologies can dynamically change.
So as an example, if on switch three are shut down, gigabit is zero one and topped show spanning tree.
What we can see now is that gigabit is zero, zero is now the root port as this port is no longer available.
If I.
No shut that interface.
And top shows spanning tree can see the interface is coming up.
What you can see now is that gigabit zero one has become the root port once again, whereas this port
is now blocking to stop a spanning tree loop.