Vlan Settings - Tripp Lite NGI-S04C2 Owner's Manual

6.6.2.

VLAN Settings

802.1Q VLAN
A virtual LAN, commonly known as a VLAN, is a group of hosts with a common set of
requirements that communicate as if they were attached to the Broadcast domain,
regardless of their physical location. A VLAN has the same attributes as a physical LAN,
but it allows for end stations to be grouped together even if they are not located on the
same network switch. In Lite Managed switches, user can configure maximum of 5
VLAN's on each interface in the format 1,3,7,10,25. Network reconfiguration can be
done through software instead of physically relocating devices.
VID- VLAN ID is the identification of the VLAN, which is basically used by the
standard 802.1Q. It has 12 bits and allow the identification of 4096 (2^12) VLANs. Of
the 4096 possible VIDs, a VID of 0 is used to identify priority frames and value 4095
(FFF) is reserved, so the maximum possible VLAN configurations are 4,094.
A tagged VLAN uses an explicit tag (VLAN ID) in the MAC header to identify the
VLAN membership of a frame across bridges - they are not confined to the switch on
which they were created. The VLANs can be created statically by hand or dynamically
through GVRP. The VLAN ID associates a frame with a specific VLAN and provides the
information that switches need to process the frame across the network. A tagged frame is
four bytes longer than an untagged frame and contains two bytes of TPID (Tag Protocol
Identifier, residing within the type/length field of the Ethernet frame) and two bytes of
TCI (Tag Control Information, starts after the source address field of the Ethernet frame).
The CFI (Canonical Format Indicator) is a single-bit flag, always set to zero for Ethernet
switches. If a frame received at an Ethernet port has a CFI set to 1, then that frame should
not be forwarded as it is to an untagged port. The remaining twelve bits define the VLAN
ID, giving a possible maximum number of 4,096 VLANs. Note that user priority and
VLAN ID are independent of each other. A frame with VID (VLAN Identifier) of null (0)
is called a priority frame, meaning that only the priority level is significant and the
default VID of the ingress port is given as the VID of the frame. Of the 4096 possible
VIDs, a VID of 0 is used to identify priority frames and value 4095 (FFF) is reserved, so
the maximum possible VLAN configurations are 4,094.
TPID
2 bytes
Forwarding Tagged and Untagged Frames

Each port on the Switch is capable of passing tagged or untagged frames. To forward a
frame from an 802.1Q VLAN-aware switch to an 802.1Q VLAN-unaware switch, the
Switch first decides where to forward the frame and then strips off the VLAN tag. To
forward a frame from an 802.1Q VLAN-unaware switch to an 802.1QVLAN-aware
switch, the Switch first decides where to forward the frame, and then inserts a VLAN tag
reflecting the ingress port's default VID. The default PVID is VLAN 1 for all ports, but
this can be changed.
User Priority
3 bits
100
CFI VLAN ID
1 bit 12 bits