802.1Q Vlan Packet Forwarding - D-Link DES-3326 User Manual

24-port NWay Ethernet Switch User's Guide
VLANs allow a network to be segmented in order to reduce the
size of broadcast domains. All packets entering a VLAN will only
be forwarded to the stations (over IEEE 802.1Q enabled switches)
that are members of that VLAN, and this includes broadcast,
multicast and unicast packets from unknown sources.
VLANs can also provide a level of security to your network. IEEE
802.1Q VLANs will only deliver packets between stations that are
members of the VLAN.
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.
The IEEE 802.1Q standard restricts the forwarding of untagged
packets to the VLAN the receiving port is a member of.
The main characteristics of IEEE 802.1Q are as follows:
Assigns packets to VLANs by filtering.
Assumes the presence of a single global spanning tree.
Uses an explicit tagging scheme with one-level tagging.

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.
58 Switch Management and Operating Concepts