VLAN - Trunk interfaces don't appear in `show vlan` output
When configuring VLANs on a switch, the show vlan command displays a list of VLANs, their names, and the ports which belong to each one.
Any ports that are configured as trunks do not appear in the output of the show vlan command. Only access ports appear in the output.
For example, the following is the output of the show vlan command on a switch that has been configured with its FastEthernet0/14 interface as a trunk, and its FastEthernet0/2 interface as an access port on VLAN 50.
SW2#show vlan VLAN Name Status Ports ---- -------------------------------- --------- ------------------------------- 1 default active Fa0/1, Fa0/3, Fa0/4, Fa0/5 Fa0/6, Fa0/7, Fa0/8, Fa0/9 Fa0/10, Fa0/11, Fa0/12, Fa0/13 Fa0/15, Fa0/22, Fa0/23, Fa0/24 Gi0/1, Gi0/2 50 Computers active Fa0/2
Notice that the FastEthernet0/14 interface does not appear at all in the output of the command because it is configured as a trunk, while FastEthernet0/2 appears under VLAN 50. The rest of the ports remain under VLAN 1 which is the default.
Links:
https://networklessons.com/switching/how-to-configure-trunk-on-cisco-catalyst-switch/