KB.15.15

Example 42 Tagged and untagged VLAN port assignments

If port 7 on an 802.1Q-compliant switch is assigned to only the Red VLAN, the assignment can

remain "untagged" because the port will forward traffic only for the Red VLAN. However, if both

the Red and Green VLANs are assigned to port 7, then at least one of those VLAN assignments

must be "tagged" so that Red VLAN traffic can be distinguished from Green VLAN traffic.

In switch X:

• VLANs assigned to ports X1 - X6 can be untagged because there is only one VLAN assignment

per port. Red VLAN traffic will go out only the Red ports, Green VLAN traffic will go out only

the Green ports, and so on. Devices connected to these ports do not have to be

802.1Q-compliant.

• However, because both the Red VLAN and the Green VLAN are assigned to port X7, at least

one of the VLANs must be tagged for this port.

In switch Y:

• VLANs assigned to ports Y1 - Y4 can be untagged because there is only one VLAN assignment

per port. Devices connected to these ports do not have to be 802.1Q-compliant.

• Because both the Red VLAN and the Green VLAN are assigned to port Y5, at least one of the

VLANs must be tagged for this port.

In both switches:

• The ports on the link between the two switches must be configured the same. As shown in

Example 43 “VLAN ID numbers assigned in the VLAN names screen”, the Red VLAN must be

untagged on port X7 and Y5 and the Green VLAN must be tagged on port X7 and Y5, or

vice-versa.

NOTE: Each 802.1Q-compliant VLAN must have its own unique VID number, and that VLAN

must be given the same VID in every device in which it is configured. That is, if the Red VLAN has

a VID of 10 in switch X, then 10 must also be the Red VID in switch Y.

54 Static Virtual LANs