Dell PowerConnect 7048P User Manual - Page 577

802.1Q (0x8100) EtherType, it allows the traffic to have added security from misconfiguration while exiting the metro core. For example, if the edge device on the other side of the metro core is not stripping the second tag, the packet would never be classified as a 802.1Q tag, so the packet would be dropped rather than forwarded in the incorrect VLAN. Figure 21-2. Double VLAN Tagging Network Example 802.1Q Domain Edge Device Edge Device Metro Core 802.1Q Domain Customer A ID = 50 Data .1Q Tag Link Vlan ID Payload Header 22 .1Q Tagged Frame Data .1Q Tag Link Vlan ID Payload Header 33 DVLAN Tagged Frame Data Link Header DVlan Tag Vlan ID 50 .1Q Tag Vlan ID Payload 22 Data Link Header DVlan Tag Vlan ID 60 .1Q Tag Vlan ID Payload 33 Customer B ID = 60 Data .1Q Tag Link Vlan ID Payload Header 22 .1Q Tagged Frame Data .1Q Tag Link Vlan ID Payload Header 33 Voice VLAN The Voice VLAN feature enables switch ports to carry voice traffic with defined priority. When multiple devices, such as a PC and an IP phone, are connected to the same port, you can configure the port to use one VLAN for voice traffic and another VLAN for data traffic. Voice over IP (VoIP) traffic is inherently time-sensitive: for a network to provide acceptable service, the transmission rate is vital. The priority level enables 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 of an IP phone is safeguarded from deteriorating when the data traffic on the port is high. The switch uses the source MAC address of the traffic traveling through the port to identify the IP phone data flow. Configuring VLANs 577