ZyXEL GS1500-24P User Guide - Page 67
Overview, What You Can Do, What You Need to Know
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CHAPTER 8 VLAN 8.1 Overview This chapter shows you how to configure static, port-based VLANs. 8.2 What You Can Do • Use the Static VLAN screen (Section 8.4 on page 70) to configure the static VLAN settings on a port. • Use the Port-Based VLAN screen (Section 8.5 on page 71) to configure the port VLAN ID (PVID) for a port. 8.3 What You Need to Know Read this section to know more about VLAN and how to configure the screens. 8.3.1 IEEE 802.1Q Tagged VLANs A tagged VLAN uses an explicit tag (VLAN ID) in the MAC header to identify the VLAN membership of a frame across bridges - they are not confined to the switch on which they were created. The VLANs can be created statically by hand or dynamically through GVRP. The VLAN ID associates a frame with a specific VLAN and provides the information that switches need to process the frame across the network. A tagged frame is four bytes longer than an untagged frame and contains two bytes of TPID (Tag Protocol Identifier, residing within the type/length field of the Ethernet frame) and two bytes of TCI (Tag Control Information, starts after the source address field of the Ethernet frame). The CFI (Canonical Format Indicator) is a single-bit flag, always set to zero for Ethernet switches. If a frame received at an Ethernet port has a CFI set to 1, then that frame should not be forwarded as it is to an untagged port. The remaining twelve bits define the VLAN ID, giving a possible maximum number of 4,096 VLANs. Note that user priority and VLAN ID are independent of each other. A GS1500-24P User's Guide 67