C
ONFIGURING
THE
S
WITCH
2-46Assigning Ports to VLANs
Before enabling VLANs for the switch, you must first assign each port to
the VLAN group(s) in which it will participate. By default all ports are
assigned to VLAN 1 as untagged ports. Add a port as a tagged port (that
is, a port attached to a VLAN-aware device) if you want it to carry traffic
for one or more VLANs and if the device at the other end of the link also
supports VLANs. Then assign the port at the other end of the link to the
same VLAN(s.) However, if you want a port on this switch to participate in
one or more VLANs, but the device at the other end of the link does not
support VLANs, then you must add this port as an untagged por t (that is,
a port attached to a VLAN-unaware device.)
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 PVID of the receiving port. 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 using
a Layer-3 router or switch.
Port-based VLANs – Port-based (or static) VLANs are manually tied to
specific ports. The switch’s forwarding decision is based on the destination
MAC address and its associated port. Therefore, to make valid forwarding
or flooding decisions, the switch must learn the relationship of the MAC
address to its related port—and thus to the VLAN—at run-time.
However, when GVRP is enabled, this process can be fully automatic.
Automatic VLAN Registration – GVRP (GARP VLAN Registration
Protocol) defines a system whereby the switch can automatically learn the
VLANs to which each endstation should be assigned. If an endstation (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