Contemporary Control Systems Compact Managed Switches Software Manual for Web Browser - Manual (Page 22)

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4.4.4.2 VLAN Tags and VLAN Identifiers (VIDs)
Each VLAN frame contains an 802.1Q VLAN tag having a VID (VLAN Identifier)
indicating to which VLAN this message belongs. The switch can be configured to allow
frames with specific VIDs to be received on specific ports within a VLAN.
VID values can range from 1 to 4094 — but only within one contiguous block of 512
values. The allowable VID blocks (ranges) are :
1–511
512–1023
1024–1535
1536–2047 2048–2559
2560–3071 3072–3583
3584–4094
Packets having VID values outside of the one defined block will be dropped.
4.4.4.3 Two Types of VLANs
The managed switch supports two types of VLANs, Port VLAN and 802.1Q VLAN. A
Port VLAN is normally used to interconnect VLAN-unaware devices (such as desktop
computers) which do not use VLAN tags. But 802.1Q VLANs require 802.1Q tags in
the frames passing through the switch.
4.4.4.4 VLANS and Trunking
A problem can occur if all of the ports in a trunk do not share the same VLAN. If two
trunk ports were in different VLANs and one port suffered a link failure, frames would
then pass through the other port. As a result, the frames would be discarded. If more
than two ports support a trunk, the problem is not quite the same because when a path
fails, the alternate path is not user selectable — thus, the alternate port might or might
not be in the same VLAN unless all of the ports in the trunk were 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.