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DES-3326S Layer 3 Fast Ethernet Switch User’s Guide
Switch Management and Operating Concepts 73
IEEE 802.1Q VLANs
Some relevant terms:
Tagging - The act of putting 802.1Q VLAN information into the
header of a packet.
Untagging - The act of stripping 802.1Q VLAN information out
of the packet header.
Ingress port - A port on a switch where packets are flowing
into the switch and VLAN decisions must be made.
Egress port - A port on a switch where packets are flowing out
of the switch, either to another switch or to an end station, and
tagging decisions must be made.
IEEE 802.1Q (tagged) VLANs are implemented on the DES-
3326S Layer 3 switch. 802.1Q VLANs require tagging, which
enables the VLANs to span an entire network (assuming all
switches on the network are IEEE 802.1Q-compliant).
Any port can be configured as either tagging or untagging. The
untagging feature of IEEE 802.1Q VLANs allow VLANs to work
with legacy switches that don’t recognize VLAN tags in packet
headers. The tagging feature allows VLANs to span multiple
802.1Q-compliant switches through a single physical
connection and allows Spanning Tree to be enabled on all ports
and work normally.
802.1Q VLAN Packet Forwarding
Packet forwarding decisions are made based upon the following
three types of rules:
• Ingress rules – rules relevant to the classification of
received frames belonging to a VLAN.