LevelOne GTL-2691 User Manual

Page 199

HAPTER

| VLAN Configuration

IEEE 802.1Q VLANs

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VLAN Classification – When the switch receives a frame, it classifies the

frame in one of two ways. If the frame is untagged, the switch assigns the

frame to an associated VLAN (based on the default VLAN ID of the

receiving port). But if the frame is tagged, the switch uses the tagged

VLAN ID to identify the port broadcast domain of the frame.

Port Overlapping – Port overlapping can be used to allow access to

commonly shared network resources among different VLAN groups, such

as file servers or printers. Note that if you implement VLANs which do not

overlap, but still need 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

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 end station 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 the

boundary ports to prevent advertisements from being propagated, or

forbid those ports from joining restricted VLANs.

OTE

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 Members to VLANs" on page 202

But you can still enable GVRP on these edge switches, as well as on the

core switches in the network.