HP 4108GL Management And Configuration Manual page 331

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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 used
for the Red VID in switch Y.
VID Numbers
Figure 14-18. Example of VLAN ID Numbers Assigned in the VLAN Names Screen
VLAN tagging gives you several options:
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For example, in the following network, switches X and Y and servers S1 and
S2 are 802.1Q-compliant. (Server S3 could also be 802.1Q-compliant, but it
makes no difference for this example.)
Since the purpose of VLAN tagging is to allow multiple VLANs on the same
port, any port that has only one VLAN assigned to it can be configured as
"Untagged" (the default).
Any port that has two or more VLANs assigned to it can have one VLAN
assignment for that port as "Untagged". All other VLANs assigned to the
same port must be configured as "Tagged". (There can be no more than
one Untagged VLAN on a port.)
If all end nodes on a port comply with the 802.1Q standard and are
configured to use the correct VID, then, you can configure all VLAN
assignments on a port as "Tagged" if doing so makes it easier to manage
your VLAN assignments, or for security reasons.
Port-Based Virtual LANs (VLANs) and GVRP
Port-Based Virtual LANs (Static VLANs)
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