User`s guide

VLAN Switch Operation
DIGITAL MultiSwitch 700 Port Based VLAN User’s Guide 2-5
Tagged Frames
In this example, the switch receives a tagged frame from Interface 4. The
switch examines the frame and notices the frame is tagged for VLAN C.
This frame may have already been through a VLAN aware switch, or
originated from a station capable of specifying a VLAN membership. If a
switch receives a frame containing a tag, the switch will classify the frame
in regard to its tag rather than the PVID for its port.
The switch will now make a forwarding decision on this frame based on
its mode of operation, as described in Section 2.4.2, Forwarding
Decisions.
2.4.2 Forwarding Decisions
The type of frame under consideration and the operational mode of a
VLAN switch determines how it forwards VLAN frames.
2.4.2.1 Broadcasts, Multicasts, and Unknown Unicasts
If a frame with a broadcast, multicast, or other unknown address is
received by a VLAN aware switch, the switch checks the VLAN
classification of the frame. The switch then forwards the frame out all
ports that are identified in the Forwarding List for that VLAN.
2.4.2.2 Known Unicasts
When a VLAN switch receives a frame with a known MAC address as its
destination address, the action taken by the switch to determine whether
the frame is transmitted depends on the operational mode of the switch.
Open Mode
A switch operating in the Open mode examines a known unicast VLAN
frame and makes its forwarding decision based on the destination MAC
address of the frame. This decision only determines if the switch can
identify a single output interface for the destination MAC address of the
frame. If such an interface is identified, the switch will then compare the
VLAN tag of the frame with the VLAN eligibilities in that interface’s
Egress List.