Contemporary Control Systems Compact Managed Switches Software Manual for Console Access - Manual (Page 19)

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4.3.5.5 Configure 802.1Q VLAN menu
Figure 12 displays the four functions of the Configure 802.1Q VLAN menu :
Status (read-only) reports whether or not VLANs are enabled on the switch.
Configure Non-802.1Q Frame Drop Rules (explained in Section 4.2.1.5.9)
Configure VLAN Groups and VID (explained in Section 4.2.1.5.7)
Configure 802.1Q VLAN Tag (explained in Section 4.2.1.5.8)
Figure 12 — Configure 802.1Q VLAN
4.3.5.6 VLANS and Trunking
A problem can occur if one of the ports in a trunk is not in the same VLAN as the other
ports in the trunk. Messages will travel over one of the ports in a trunk, but this port
cannot be selected by the user. Messages could also pass successfully through a trunk
via a port in the VLAN — but if that link becomes disrupted, messages would pass
through another trunk port that may not be in the same VLAN. Therefore all of the ports
in a trunk must be in the same VLAN.
Therefore, the rule when using trunking and VLANs is for all ports in the trunk to be in
the same VLAN and have the same default VID number — and every port in potential
use should have a VLAN defined for it.