HP procurve series 4100gl Management And Configuration Manual page 264

Port-Based Virtual LANs (VLANs) and GVRP
Port-Based Virtual LANs (Static VLANs)
11-24
VLAN tagging gives you several options:
I 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
I
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
I
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.
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.)
Server
S1
Red VLAN: Untagged
Green VLAN: Tagged
X1
Switch
X2
"X"
X4 X3
Red Green
VLAN VLAN
Figure 11-19. Example of Networked 802.1Q-Compliant Devices with Multiple
VLANs on Some Ports
Server
S2
Red VLAN: Untagged
Green VLAN: Tagged
Red VLAN: Untagged
Y1
Green VLAN: Tagged
Switch
Y5
"Y"
Y4
Red
VLAN
Green VLAN only
Server
Y2
S3
Y3
Green
VLAN