User’s Manual of GS-5220 LCD Series
187
This Managed Switch supports the following VLAN features:
Up to 255 VLANs based on the IEEE 802.1Q standard
Port overlapping, allowing a port to participate in multiple VLANs
End stations can belong to multiple VLANs
Passing traffic between VLAN-aware and VLAN-unaware devices
Priority tagging
■ IEEE 802.1Q Standard
IEEE 802.1Q (tagged) VLAN are implemented on the Switch. 802.1Q VLAN require tagging, which enables them
to span the entire network (assuming all switches on the network are IEEE 802.1Q-compliant).
VLAN 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.
VLAN can also provide a level of security to your network. IEEE 802.1Q VLAN 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 VLAN allows VLAN to work with legacy switches that don't recognize
VLAN tags in packet headers.
The tagging feature allows VLAN 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.
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.
■ 802.1Q VLAN Tags
The figure below shows the 802.1Q VLAN tag. There are four additional octets inserted after the source MAC
address. Their presence is indicated by a value of 0x8100 in the Ether Type field. When a packet's Ether Type
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