Example of Networked 802.1Q-compliant devices with multiple VLANs on some ports
In the following network, switches X and Y and servers S1, S2, and the AppleTalk server are 802.1Q-compliant. (Server S3 could also be 802.1Q-compliant, but it makes no difference for this example.) This network includes both protocol-based (AppleTalk) VLANs and port-based VLANs.

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The VLANs assigned to ports X4 - X6 and Y2 - Y5 can all be untagged because there is only one VLAN assigned per port.
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Port X1 has two AppleTalk VLANs assigned, which means that one VLAN assigned to this port can be untagged and the other must be tagged.
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Ports X2 and Y1 have two port-based VLANs assigned, so one can be untagged and the other must be tagged on both ports.
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Ports X3 and Y6 have two port-based VLANs and one protocol-based VLAN assigned. Thus, one port-based VLAN assigned to this port can be untagged and the other must be tagged. Also, since these two ports share the same link, their VLAN configurations must match.
Switch X | Switch Y | ||||||||
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Port | AT-1 VLAN | AT-2 VLAN | Red VLAN | Green VLAN | Port | AT-1 VLAN | AT-2 VLAN | Red VLAN | Green VLAN |
X1 | Untagged | Tagged | No | No | Y1 | No | No | Untagged | Tagged |
X2 | No | No | Untagged | Tagged | Y2 | No | No | No | Untagged |
X3 | No | Untagged | Untagged | Tagged | Y3 | No | Untagged | No | No |
X4 | No | No | No | Untagged | Y4 | No | No | No | Untagged |
X5 | No | No | Untagged | No | Y5 | No | No | Untagged | No |
X6 | Untagged | No | No | No | Y6 | No | Untagged | Untagged | Tagged |
VLAN configurations on ports connected by the same link must match. Because ports X2 and Y5 are opposite ends of the same point-to-point connection, both ports must have the same VLAN configuration, configuring the Red VLAN as "Untagged" and the Green VLAN as "Tagged.”