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We can confirm which ports are trunking on our switches by as an example going onto switch one and tapping

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show interfaces trunk.

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As you can see here, the command show interface trunk shows me that gigabit 001, two and three are

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set on for trunking using ED one q.

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The status is trunking and the native VLAN is VLAN one.

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The VLANs allowed across those ports of VLANs 1 to 4094.

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In other words, we've allowed all VLANs, the VLANs currently allowed and active in the management

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domain are 110 and 20.

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VLANs, in the spanning tree forwarding state to not pruned are 110 and 20.

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We'll talk about spanning tree in a moment.

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But this port is the only port that is forwarding traffic across it because port one and two are currently

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blocked as shown here because Port one, two and three are currently blocked through spanning tree shows,

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spanning tree, as an example, shows me that those ports are blocking this port is not a trunk port.

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This is an access port.

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So show interface trunk.

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Shows me in a nice simple format which interfaces are configured for trunking, which encapsulation

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is used, and which ports are forwarding for which VLANs?

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Let's have a look at switch to as an example.

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On switch to show interface trunk.

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Put gigabit 000102 and zero three.

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So these interfaces are trunking.

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The mode is on.

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We're not using http encapsulation is dot one Q status trunking native VLAN is VLAN one.

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The VLANs allowed across those ports are 1 to 4094.

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Currently the VLANs allowed and active in the management domain or 110 and 20 VLANs in spanning tree

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forwarding state are not pruned are 110 and 20 across all the ports at the moment.

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Show VLAN brief shows me that I only have VLAN 110 and 20 configured on the switch and hence the switch

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is forwarding those VLANs across those ports.

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110 and 20 is forwarded across port gigabit zero one, two and three spanning trees are not blocking

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any of these ports.

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And I can see that by tapping QoS spanning tree.

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As you can see here, all those ports are forwarding and they are designated ports because the switch

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is the route switch, whereas on switch one once again shows spanning tree shows me that the switch

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is not the route bridge or route switch of the spanning tree.

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These ports one, two and three.

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So one, two and three are blocking show interface trunk shows me that those ports are trunk ports.

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But only gigabit.

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Zero zero is forwarding vlans 110 and 20 across it.

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So show interfaces trunk is a very useful command to see a summary of your trunks.