Technical basics
4.5 VLAN
SCALANCE W780/W740 to IEEE 802.11n Web Based Management
Configuration Manual, 08/2018, C79000-G8976-C267-13
55
VLAN
Network definition regardless of the spatial location of the nodes
VLAN (Virtual Local Area Network) divides a physical network into several logical networks
that are shielded from each other. Here, devices are grouped together to form logical groups.
Only nodes of the same VLAN can address each other. Since multicast and broadcast
frames are only forwarded within the particular VLAN, they are also known as broadcast
domains.
The particular advantage of VLANs is the reduced network load for the nodes and network
segments of other VLANs.
For the identifier which frame is assigned to which VLAN, the frame is expanded by 4 bytes
(VLAN tagging). Apart from the VLAN-ID this expansion also includes priority information.
Options for the VLAN assignment
There are various options for the assignment to VLANs:
● Port-based VLAN
Each port of a device is assigned a VLAN ID. You configure port-based VLAN in "Layer 2
> VLAN (Page 331)".
● Protocol-based VLAN
Each port of a device is assigned a protocol group.
● Subnet-based VLAN
The IP address of the device is assigned a VLAN ID.
Doubly tagged frame (Q-in-Q)
There are devices e.g. SCALANCE XR500 that support the Q-in-Q function. With the Q-in-Q
function the incoming data traffic is treated as if it were untagged. With frames that are
already tagged
①, this means they are expanded by a second VLAN tag, the outer VLAN
tag
②.
When a SCALANCE W device receives a doubly tagged frame, it uses the VLAN ID from the
outer VLAN tag
② and the priority information from the inner VLAN tag ①. The frame is
then forwarded to the relevant VLAN.
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