Interlogix NS3550-2T-8S User Manual - Manual (Page 125)

IFS NS3552-8P-2S AND NS3550-2T-8S User Manual
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to the same physical segment.
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
 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 field is equal to 0x8100, the
packet carries the IEEE 802.1Q/802.1p tag. The tag is contained in the following two octets and consists of 3 bits of user priority,
1 bit of Canonical Format Identifier (CFI - used for encapsulating Token Ring packets so they can be carried across Ethernet