Cabletron Systems SmartSTACK ELS100 - Manual (Page 98)

84 Virtual LANs (VLANs) ELS100-24TX
If the ELS100-24TX is so configured, and, if the frame does not already
contain a tag, a VLAN identifier is placed in a tag which is appended to
frames as they are received by the switch. Within the switch and between
switches compliant with IEEE 802.1Q, these identifiers are used to control
the destination of broadcast frames, preventing them from being flooded
to all connected stations and interfaces. When frames are forwarded back
to destination end stations, the tag may or may not be stripped off,
depending on the configuration of the end station and the switch port.
By using 802.1Q tagged VLANs, users from physically dispersed
locations can be formed into groups by assigning them to specific VLANs.
Broadcast and multicast traffic for these specific VLANs can be directed
across the network without being radiated out to stations that are not
members of the same VLANs. Up to 4094 different VLANs can be
specified by the 802.1Q tag, thus permitting the configuration of up to
4094 virtual workgroups. This implementation is nonintrusive to end-
station applications and the associated clients.
ELS100-24TX VLAN Configuration
VLAN operation on the ELS100-24TX is disabled by default. When
VLANs are enabled, all frames are transferred internally through the
switch with a VLAN tag. This tag may already be on the frame entering
the switch, or added to the frame by the switch. VLAN information already
existing on frames entering the switch is automatically handled by the
switch. The ELS100-24TX learns VLAN information from tagged frames
and appropriately switches frames out the proper ports based on this
information. The configuration of VLANs for frames entering the switch
without tags must be made by the user of the switch. This configuration
can be made either through the VLAN Menu in the console interface or
via SNMP. The parameters used to configure VLANs on the ELS100-
24TX are explained below.
VLAN ID
The VLAN ID is used to uniquely identify different VLANs on a network.
The VLAN ID information is contained in the 802.1Q tag header on a
frame, and so identifies the VLAN to which a frame belongs. The ELS100-
24TX recognizes VLAN IDs in the tags on frames entering the switch, and
can also add tags with an appropriate VLAN ID to untagged frames.
Ports in VLAN
When configuring VLANs on the ELS100-24TX, individual ports are
assigned to specific VLANs by setting the Port VLAN ID (PVID) for each
port. Frames entering the switch which are untagged are automatically
assigned a VLAN ID by the switch based on the PVID of the incoming
port. The Ports in VLAN parameter makes the assignment of ports to
PVIDs. An individual port can only be assigned to a single PVID with this
parameter.