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of the VLAN, the frame is forwarded to the destination port. If the incoming frame is not
tagged with VLAN information, the ingress port will use PVID as the VLAN ID. If the
destination port is not in the same VLAN, the frame is dropped.
The switch is initially configured to have one VLAN and its VID is 1. This VLAN is called
the default VLAN. By default, all ports are initially assigned to the default VLAN.
Frames can not be forwarded across VLANs. Frames, whether they are unicast,
multicast or broadcast, cannot flow from one VLAN to another VLAN unless there is a
VLAN routing device to bridge them.
The switch also allows a user to configure the egress packets to either tagging or
untagging. The untagging feature of 802.1Q VLAN allows a user to hook up the port to a
legacy switch that doesn't recognize 802.1Q tagging header in the packet. Also, the
tagging feature allows VLANs to span into multiple 802.1Q compliant switches through
physical connections between switches.
Chapter 6: 1-Gb Ethernet Switch Firmware
6-11
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