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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 VH-
2402-L3 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.
•
Forwarding rules between ports – decides filter or forward
the packet
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VH-2402-L3 Management Guide 129
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