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User’s Manual of SGSD-1022 / SGSD-1022P
SGSW-2840 / SGSW-2840P
176
VLANs, and any intermediate network devices or the host at the other end of the connection supports VLANs. Then assign ports
on the other VLAN-aware network devices along the path that will carry this traffic to the same VLAN(s), either manually or
dynamically using GVRP. However, if you want a port on this switch to participate in one or more VLANs, but none of the
intermediate network devices nor the host at the other end of the connection supports VLANs, then you should add this port to
the VLAN as an untagged port.
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.
■ 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 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