570 Configuring VLANsdefault PVID of the port, and the voice traffic is received tagged with thepredefined VLAN. As a result, both kinds of traffic are segregated in orderto provide better service to the voice traffic.• When a dot1p priority is associated with the Voice VLAN port instead of aVLAN ID, then the priority information is passed onto the VoIP phoneusing the LLDP-MED or CDP mechanism. By this method, the voice datacoming from the VoIP phone is tagged with VLAN 0 and with theexchanged priority; thus regular data arriving on the switch is given thedefault priority of the port (default 0), and the voice traffic is received witha higher priority.You can configure the switch to override the data traffic CoS. This feature canoverride the 802.1 priority of the data traffic packets arriving at the portenabled for Voice VLAN. Therefore, any rogue client that is also connected tothe Voice VLAN port does not deteriorate the voice traffic.Voice VLAN and LLDP-MEDThe interactions with LLDP-MED are important for Voice VLAN:• LLDP-MED notifies the Voice VLAN component of the presence andabsence of a VoIP phone on the network.• The Voice VLAN component interacts with LLDP-MED for applyingVLAN ID, priority, and tag information to the VoIP phone traffic.Private VLANsPrivate VLANs partition a standard VLAN domain into two or moresubdomains. Each subdomain is defined by a primary VLAN and a secondaryVLAN. The primary VLAN ID is the same for all subdomains that belong to aparticular private VLAN instance. The secondary VLAN ID differentiates thesubdomains from each other and provides layer 2 isolation between ports onthe same private VLAN.The following types of VLANs can be configured in a private VLAN:• Primary VLAN—Forwards the traffic from the promiscuous ports toisolated ports, community ports and other promiscuous ports in the sameprivate VLAN. Only one primary VLAN can be configured per privateVLAN. All ports within a private VLAN share the same primary VLAN.
