D-Link DGS-3324SRi Intelligent Stackable Gigabit Ethernet Switch
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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
allows 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.
•
Forwarding rules between ports – decides whether to filter or forward the packet.
•
Egress rules – determines if the packet must be sent tagged or untagged.
Figure 4- 17. IEEE 802.1Q Packet Forwarding