VLAN Classification
– When the switch receives a frame, it classifies the frame in
one of two ways. If the frame is untagged, th e switch assi gns the fra me to an
associated VLAN (based on the default VLAN ID of the receiving po rt). But if the
frame is tagged, the switch uses the tagged VLAN ID to id entify the po rt broad cast
domain of the frame.
Port Overlapping
– Port overlapping can be used to allow access to co mmonly
shared network resources among different VLAN gro ups, such as file s ervers o r
printers. Note that if you implement VLA Ns which do no t overl ap, but still ne ed to
communicate, you can connect them by enabled routing on this switch.
Untagged VLANs
– Untagged (or static) VLANs are typically used to reduce
broadcast traffic and to increase security. A group of network users assigned to a
VLAN form a broadcast domain that is separate from other VLA Ns configured on the
switch. Packets are forwarded only between ports that are designated for the same
VLAN. Untagged VLANs can be used to manually isolate user groups or subnets.
However, you should use IEEE 802.3 tagged VLANs with GVRP whenever possible
to fully automate VLAN registration.
Automatic VLAN Registration
– GVRP (GARP VLAN Registration Protocol)
defines a system whereby the switch can automatically learn the VL ANs to which
each end station should be assigned. If an end station (or its network adapte r)
supports the IEEE 802.1Q VLAN protocol, it can be configu red to broa dcast a
message to your network indicating the VLAN groups it wants to join. When t his
switch receives these messages, it will automatically place the receivin g port in the
specified VLANs, and then forward the message to all other ports. When the
message arrives at another switch that supports GVRP, it will also place the
receiving port in the specified VLANs, and pass the messag e on to all other ports.
VLAN requirements are propagated in this way throughout the network. This allows
GVRP-compliant devices to be automatically configured for VLAN groups based
solely on endstation requests.
To implement GVRP in a network, first add the host devices to the required VLANs
(using the operating system or other application software), so that these VLANs can
be propagated onto the network. For both the edge switches attache d directly to
11-2
Note:
VLAN-tagged frames can pass through VLAN-aware or VLAN-unaware network
interconnection devices, but the VLAN tags should be stripped off before passing it
on to any end-node host that does not support VLAN tagging.
tagged frames
V
A
V
A
VA
VA: VLAN Aware
VU: VLAN Unaware
VU
tagged untagged
frames frames
VA
VLAN Configuration
11