I have a Cisco ASA 5520 which has a 3750 trunked off it (see diagram, ingore the ASA standby).
Everything is working, but I can see the follwoing vlans are allowed through the trunk - 3,4,6,7,9,10,300, but vlan 2 isn't in this allow list and it still works.
switchport trunk encapsulation dot1q
switchport trunk allowed vlan 3,4,6,7,9,10,300
switchport mode trunk
I'm doing a packet capture on this port and what to filter traffic based on vlan tag ID, but vlan 2 doesn't show up in the capture only the ones mentioned above.