We can confirm which ports are trunking on our switches by as an example going onto switch one and tapping
show interfaces trunk.
As you can see here, the command show interface trunk shows me that gigabit 001, two and three are
set on for trunking using ED one q.
The status is trunking and the native VLAN is VLAN one.
The VLANs allowed across those ports of VLANs 1 to 4094.
In other words, we've allowed all VLANs, the VLANs currently allowed and active in the management
domain are 110 and 20.
VLANs, in the spanning tree forwarding state to not pruned are 110 and 20.
We'll talk about spanning tree in a moment.
But this port is the only port that is forwarding traffic across it because port one and two are currently
blocked as shown here because Port one, two and three are currently blocked through spanning tree shows,
spanning tree, as an example, shows me that those ports are blocking this port is not a trunk port.
This is an access port.
So show interface trunk.
Shows me in a nice simple format which interfaces are configured for trunking, which encapsulation
is used, and which ports are forwarding for which VLANs?
Let's have a look at switch to as an example.
On switch to show interface trunk.
Put gigabit 000102 and zero three.
So these interfaces are trunking.
The mode is on.
We're not using http encapsulation is dot one Q status trunking native VLAN is VLAN one.
The VLANs allowed across those ports are 1 to 4094.
Currently the VLANs allowed and active in the management domain or 110 and 20 VLANs in spanning tree
forwarding state are not pruned are 110 and 20 across all the ports at the moment.
Show VLAN brief shows me that I only have VLAN 110 and 20 configured on the switch and hence the switch
is forwarding those VLANs across those ports.
110 and 20 is forwarded across port gigabit zero one, two and three spanning trees are not blocking
any of these ports.
And I can see that by tapping QoS spanning tree.
As you can see here, all those ports are forwarding and they are designated ports because the switch
is the route switch, whereas on switch one once again shows spanning tree shows me that the switch
is not the route bridge or route switch of the spanning tree.
These ports one, two and three.
So one, two and three are blocking show interface trunk shows me that those ports are trunk ports.
But only gigabit.
Zero zero is forwarding vlans 110 and 20 across it.
So show interfaces trunk is a very useful command to see a summary of your trunks.