802.1Q Vlan Tagging - HP ProCurve 5300xl Series Management Manual

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Static Virtual LANs (VLANs)

802.1Q VLAN Tagging

General Applications:

The switch requires VLAN tagging on a given port if more than one VLAN

of the same type uses the port. When a port belongs to two or more VLANs

of the same type, they remain as separate broadcast domains and cannot

receive traffic from each other without routing. (If multiple, non-routable

VLANs exist in the switch—such as NETbeui protocol VLANs— then they

cannot receive traffic from each other under any circumstances.)

The switch requires VLAN tagging on a given port if the port will be

receiving inbound, tagged VLAN traffic that should be forwarded. Even if

the port belongs to only one VLAN, it forwards inbound tagged traffic only

if it is a tagged member of that VLAN.

If the only authorized, inbound VLAN traffic on a port arrives untagged,

then the port must be an untagged member of that VLAN. This is the case

where the port is connected to a non 802.1Q-compliant device or is

assigned to only one VLAN.

For example, 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. Figure 2-24 shows this concept:

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