HP 6120XG HP ProCurve Series 6120 Blade Switches Advanced Traffic Management G - Page 63

Static Virtual LANs (VLANs) 802.1Q VLAN Tagging 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 2-26 shows this concept: 2-40