Interlogix NS3500-28T-4S User Manual - Manual (Page 111)

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VLANs help to simplify network management by allowing you to move devices to a new VLAN without having to
change any physical connections. VLANs can be easily organized to reflect departmental groups (such as Marketing
or R&D), usage groups (such as e-mail), or multicast groups (used for multimedia applications such as
videoconferencing).
VLANs provide greater network efficiency by reducing broadcast traffic, and allow you to make network changes
without having to update IP addresses or IP subnets. VLANs inherently provide a high level of network security since
traffic must pass through a configured Layer 3 link to reach a different VLAN.
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
■ 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 field is equal to