Vlan - WAGO 852-1305 Manual

WAGO-ETHERNET-Zubehör 852
852-1305 8/4-Port 100BASE-T/1000BASE-SX/LX
7.2.3

VLAN

A VLAN ("Virtual LAN") is a group of hosts with a common set of requirements
that communicate as if they were attached to a 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. Networks can be reconfigured through software instead of
spatially offset devices.
VID ("VLAN-ID") is the identification of a VLAN that is generally used by the
802.1Q standard. It has 12 bits and allows the identification of 4096 (2^12)
VLANs. Of the 4096 possible VIDs, VID 0 is used to identify "Priority Frames"
and value 4095 (FFF) is reserved, so the maximum possible VLAN configurations
are 4094.
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. VLANs can be created
statically (manually by users) or dynamically via the GVRP ("GARP VLAN
Registration Protocol"). 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 of 1,
the frame should not be output to an untagged port. The remaining 12 bits define
the VLAN ID, giving a possible maximum number of 4096 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", i.e., only the priority
level is relevant and the default VID of the ingress port is used 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 4094.
TPID
2 bytes
Manual
1.1.0
User Priority
3 Bit
Enhanced Features
CFI VLAN ID
1 bits 12 bits
67