Static Virtual LANs (VLANs)

802.1Q VLAN Tagging

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 either makes it easier to manage your VLAN assignments, or if the authorized, inbound traffic for all VLANs on the port will be tagged.

For a summary and flowcharts of untagged and tagged VLAN operation on inbound traffic, refer to the following under “VLAN Operating Rules” on pages

2-13through 2-16:

“Inbound Tagged Packets”

“Untagged Packet Forwarding” and figure 2-7

“Tagged Packet Forwarding” and figure 2-8

Example. 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.

AT1 (Protocol) VLAN:

Untagged

AppleTalk

 

System

 

 

 

 

 

 

 

 

 

System

 

 

 

 

 

 

 

 

Server

 

Server S1

 

 

 

 

 

 

 

 

 

Server S2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Red VLAN: Untagged

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Green VLAN: Tagged

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

X1

 

X2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Y1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Green VLAN

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Switch

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Switch

 

 

 

 

Only

 

 

 

 

 

X3

 

 

 

 

 

 

 

Y6

Y2

 

 

System

 

“X”

 

 

 

 

 

 

 

 

 

“Y”

 

 

 

 

Server S3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

X6

X5

 

X4

 

Red VLAN: Untagged

 

 

Y5

Y4

Y3

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Green VLAN: Tagged

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

AT2 (Protocol) VLAN:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Untagged

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Apple

Red

Green

Red

Green

Apple

Talk

 

Talk

 

VLAN

VLAN

VLAN

VLAN

VLAN

1

VLAN 2

 

 

 

 

Figure 2-28. Example of Networked 802.1Q-Compliant Devices with MultipleVLANs on Some Ports

2-43