718 VLAN Commandstwo TPID values can be different or the same. VLAN normalization, sourceMAC learning, and forwarding are based on the S-TAG value in a receivedframe.PowerConnect supports configuring one outer VLAN TPID value per switch.The global default TPID is 0x88A8, which indicates a Virtual MetropolitanArea Network (VMAN).Independent VLAN LearningIndependent VLAN Learning (IVL) allows unicast address-to-port mappingsto be created based on a MAC Address in conjunction with a VLAN ID.This arrangement associates the MAC Address only with the VLAN on whichthe frame was received. Therefore, frames are forwarded based on theirunicast destination address as well as their VLAN membership. Thisconfiguration affords multiple occurrences of an address in the forwardingdatabase. Each address associates with a unique VLAN. Care must be takenin the administration of networks, as multiple instances of a MAC address,each on a different VLAN, can quickly eat up address entries.Each VLAN is associated with its own forwarding database. Hence thenumber of forwarding databases equals the number of VLANs supported.The MAC address stored is supplemented by a 2-byte VLAN ID. The first 2bytes of a forwarding database entry contain the VLAN ID associated, and thenext 6 bytes contain the MAC address. There is a one-to-one relationshipbetween VLAN ID and FID (forwarding database ID).Protocol Based VLANsThe main purpose of Protocol-based VLANs (PBVLANs) is to selectivelyprocess packets based on their upper-layer protocol by setting up protocol-based filters. Packets are bridged through user-specified ports based on theirprotocol.In PBVLANs, the VLAN classification of a packet is based on its protocol (IP,IPX, NetBIOS, and so on). PBVLANs help optimize network traffic becauseprotocol-specific broadcast messages are sent only to end stations using thatprotocol. End stations do not receive unnecessary traffic, and bandwidth isused more efficiently. It is a flexible method that provides a logical groupingof users. An IP subnet or an IPX network, for example, can each be assigned
