Chapter 15 Vlan Screens; Vlan Introduction; Ieee 802.1Q Tagged Vlan - ZyXEL Communications MSC1000G User Manual

15.1 VLAN Introduction

A VLAN (Virtual Local Area Network) allows a physical network to be partitioned into
multiple logical networks. Devices on a logical network belong to one group. A device can
belong to more than one group. With VLAN, a device cannot directly talk to or hear from
devices that are not in the same group(s); the traffic must first go through a router.
In MTU (Multi-Tenant Unit) applications, VLAN is vital in providing isolation and security
among the subscribers. When properly configured, VLAN prevents one subscriber from
accessing the network resources of another on the same LAN, thus a user will not see the
printers and hard disks of another user in the same building. If you have enabled port isolation
in the Switch Setup screen, you do not need to configure the VLAN to isolate subscribers.
VLAN also increases network performance by limiting broadcasts to a smaller and more
manageable logical broadcast domain. In traditional switched environments, all broadcast
packets go to each and every individual port. With VLAN, all broadcasts are confined to a
specific broadcast domain.

15.2 IEEE 802.1Q Tagged VLAN

The IEEE 802.1Q Tagged VLAN uses both explicit and implicit tagging.
1 Explicit Tagging
A VLAN identifier is added to the frame header that identifies the source VLAN.
2 Implicit Tagging
The MAC (Media Access Control) number, the port or other information is used to
identify the source of a VLAN frame.
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).

Chapter 15 VLAN Screens

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