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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
VLANs 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
VLANs to which each end station should be assigned. If an end station (or
its network adapter) supports the IEEE 802.1Q VLAN protocol, it can be
configured to broadcast a message to your network indicating the VLAN
groups it wants to join. When this switch receives these messages, it will
automatically place the receiving 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 message 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 attached directly to these hosts, and core switches
in the network, enable GVRP on the links between these devices. You
should also determine security boundaries in the network and disable
GVRP on ports to prevent advertisements being propagated, or forbid
ports from joining restricted VLANs.
Note: If you have host devices that do not support GVRP, you should
configure static or untagged VLANs for the switch ports
connected to these devices (as described in “Adding Static
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