Configuring VLANs 581802.1Q (0x8100) EtherType, it allows the traffic to have added security frommisconfiguration while exiting the metro core. For example, if the edgedevice on the other side of the metro core is not stripping the second tag, thepacket would never be classified as a 802.1Q tag, so the packet would bedropped rather than forwarded in the incorrect VLAN.Figure 21-2. Double VLAN Tagging Network ExampleVoice VLANThe Voice VLAN feature enables switch ports to carry voice traffic withdefined priority. When multiple devices, such as a PC and an IP phone, areconnected to the same port, you can configure the port to use one VLAN forvoice traffic and another VLAN for data traffic.Voice over IP (VoIP) traffic is inherently time-sensitive: for a network toprovide acceptable service, the transmission rate is vital. The priority levelenables the separation of voice and data traffic coming onto the port.A primary benefit of using Voice VLAN is to ensure that the sound quality ofan IP phone is safeguarded from deteriorating when the data traffic on theport is high. The switch uses the source MAC address of the traffic travelingthrough the port to identify the IP phone data flow.DataLinkHeader.1Q TagVlan ID22PayloadDataLinkHeader.1Q TagVlan ID22PayloadDVlanTagVlan ID50DataLinkHeader.1Q TagVlan ID33PayloadDVlanTagVlan ID60DataLinkHeader.1Q TagVlan ID33PayloadCustomer AID = 50802.1Q DomainMetro Core.1Q Tagged FrameDVLAN Tagged FrameEdge Device Edge Device802.1Q DomainDataLinkHeader.1Q TagVlan ID22PayloadDataLinkHeader.1Q TagVlan ID33PayloadCustomer BID = 60.1Q Tagged Frame
