Allied Telesis Rapier Switch - Manual (Page 36)

36 Rapier Switch User Guide
Rapier Switch Software Release 2.2.1
C613-02013-00 Rev A
indicating whether a VLAN is up or down, is passed to the Internet Protocol
(IP) module. IP uses this information to determine route availability.
By default the switch is configured to include all ports as untagged members of
a single default VLAN, with no VLAN tagging required on incoming frames,
or added to outgoing frames. This default VLAN cannot be deleted from the
switch. If all the devices on the physical LAN are to belong to the same logical
LAN, that is, the same broadcast domain, then the default settings will be
acceptable, and no additional VLAN configuration is required.
The ability to decouple logical broadcast domains from the physical wiring
topology offers several advantages, which include:
■ Workstations can be grouped logically or functionally, regardless of their
physical location on the network.
■ VLAN memberships can be changed at any time by software
configuration, without moving the workstations physically, or by simply
moving a cable from one port to another.
■ By using VLAN tagging, network servers or other network resources can
be shared between different work groups without losing data isolation or
security.
■ One port on the switch can be configured as an uplink to another 802.1Q-
compatible switch. By using VLAN tagging, this one port can carry traffic
from all VLANs on the switch. (With port based VLANs, one uplink port is
required to uplink each VLAN to another switch.)
VLANs can consist of simple logical groupings of untagged ports, in which the
ports receive and transmit untagged packets. Alternatively, VLANs can
include tagged ports, which add VLAN tags to packets they transmit. A port
can transmit either untagged packets or VLAN tagged packets to a VLAN of
which it is a member, but not both. A port can be tagged for more than one
VLAN, so that a single port can be used to uplink several VLANs to another
compatible switch.
A VLAN can contain a mixture of VLAN tagged and untagged ports.
The switch is VLAN aware, in that it can accept VLAN tagged frames, and
supports the VLAN switching required by such tags. A network can contain a
mixture of VLAN aware devices, for instance other 802.1Q compatible
switches, and VLAN unaware devices, for instance, workstations and legacy
switches that do not support VLAN tagging. The switch can be configured to
send VLAN tagged or untagged frames on each port, depending on whether or
not the devices connected to the port are VLAN aware. By assigning a port to
two different VLANs, to one as an untagged port and to another as a tagged
port, it is possible for the port to transmit both VLAN-tagged and untagged
frames. A port can be untagged for zero or one VLAN, and can be tagged for
zero or more different VLANs. A port must belong to a VLAN at all times
unless the port has been set as the mirror port for the switch.
A port can belong to only one Spanning Tree entity (STP), and STP
membership is per VLAN. A port cannot be added to a VLAN that is in a
different STP from the VLANs to which the port already belongs, with one
exception. The exception is that an untagged port in the default VLAN, that is
not tagged for any other VLANs, can be moved from the default VLAN to any
other VLAN in any STP.