Vlan Tagging - Siemens SIMATIC NET SCALANCE S615 Configuration Manual

Technical basics
3.3 VLAN
3.3.2

VLAN tagging

Expansion of the Ethernet frames by four bytes
For CoS (Class of Service, frame priority) and VLAN (virtual network), the IEEE 802.1Q
standard defined the expansion of Ethernet frames by adding the VLAN tag.
Note
The VLAN tag increases the permitted total length of the frame from 1518 to 1522 bytes.
The end nodes on the networks must be checked to find out whether they can process this
length / this frame type. If this is not the case, only frames of the standard length may be sent
to these nodes.
The additional 4 bytes are located in the header of the Ethernet frame between the source
address and the Ethernet type / length field:
Figure 3-1 Structure of the expanded Ethernet frame
The additional bytes contain the tag protocol identifier (TPID) and the tag control information
(TCI).
Tag protocol identifier (TPID)
The first 2 bytes form the Tag Protocol Identifier (TPID) and always have the value 0x8100. This
value specifies that the data packet contains VLAN information or priority information.
Tag Control Information (TCI)
The 2 bytes of the Tag Control Information (TCI) contain the following information:
QoS Trust
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SCALANCE S615 Web Based Management
Configuration Manual, 11/2019, C79000-G8976-C388-08