3Com 3C17300A Implementation Guide - Page 68
Creating New VLANs, VLANs: Tagged and Untagged Membership
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68 CHAPTER 8: SETTING UP VIRTUAL LANS Figure 16 Two VLANS connected via a router Creating New VLANs If you want to move a port from the Default VLAN to another VLAN, you must first define information about the new VLAN on your Switch. VLANs: Tagged and Untagged Membership Your Switch supports 802.1Q VLAN tagging, a system that allows traffic for multiple VLANs to be carried on a single physical (backbone) link. When setting up VLANs you need to understand when to use untagged and tagged membership of VLANs. Quite simply, if a port is in a single VLAN it can be an untagged member but if the port needs to be a member of multiple VLANs tagged membership must be defined. Typically endstations (for example, clients or servers) will be untagged members of one VLAN, while inter-Switch connections will be tagged members of all VLANs. The IEEE 802.1Q standard defines how VLANs operate within an open packet-switched network. An 802.1Q compliant packet carries additional information that allows a switch to determine to which VLAN the port belongs. If a frame is carrying the additional information, it is known as tagged. To carry multiple VLANs across a single physical (backbone) link, each packet must be tagged with a VLAN identifier so that the Switches can