Static Virtual LANs (VLANs)

Port-Based Virtual LANs (Static VLANs)

VLAN tagging gives you several options:

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.

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

Server

 

 

S1

 

 

S2

 

 

Red VLAN: Untagged

 

 

Red VLAN: Untagged

 

Green VLAN: Tagged

 

 

Green VLAN: Tagged

 

X1

Red VLAN: Untagged

 

Y1

 

 

 

 

Green VLAN: Tagged

 

 

 

Green VLAN only

Server

Switch X2

Y5

Switch Y2

"X"

 

 

"Y"

 

S3

X4

X3

 

Y4

Y3

 

Red

Green

Red

 

Green

 

VLAN

VLAN

VLAN

 

VLAN

 

Figure 2-23. Example of Networked 802.1Q-Compliant Devices with Multiple VLANs on Some Ports

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