NETGEAR GS748T - Page 276

276
GS748T Smart Switch
VLANs have a number of advantages:
• It is easy to do network segmentation. Users that communicate most frequently with each
other can be grouped into common VLANs, regardless of physical location. Each group’s
traffic is contained largely within the VLAN, reducing extraneous traffic and improving the
efficiency of the whole network.
• They are easy to manage. The addition of nodes, as well as moves and other changes,
can be dealt with quickly and conveniently from a management interface rather than from
the wiring closet.
• They provide increased performance. VLANs free up bandwidth by limiting node-to-node
and broadcast traffic throughout the network.
• They ensure enhanced network security. VLANs create virtual boundaries that can be
crossed only through a router. So standard, router-based security measures can be used
to restrict access to each VLAN.
Packets received by the switch are treated in the following way:
• When an untagged packet enters a port, it is automatically tagged with the port’s default
VLAN ID tag number. Each port has a default VLAN ID setting that is user configurable
(the default setting is 1). The default VLAN ID setting for each port can be changed in the
Port PVID Configuration screen. See
Port VLAN ID Configuration on page 89.
• When a tagged packet enters a port, the tag for that packet is unaffected by the default
VLAN ID setting. The packet proceeds to the VLAN specified by its VLAN ID tag number.
• If the port through which the packet entered does not have membership with the VLAN
specified by the VLAN ID tag, the packet is dropped.
• If the port is a member of the VLAN specified by the packet’s VLAN ID, the packet can be
sent to other ports with the same VLAN ID.
• Packets leaving the switch are either tagged or untagged, depending on the setting for
that port’s VLAN membership properties. A U for a given port means that packets leaving
the switch from that port are untagged. Inversely, a T for a given port means that packets
leaving the switch from that port are tagged with the VLAN ID that is associated with the
port.
The example given in this section comprises numerous steps to illustrate a wide range of
configurations to help provide an understanding of tagged VLANs.