24.1.5 VLAN Tag

<Structure of this section>

(1) Overview

VLAN tagging based on the IEEE 802.1Q standard, in which IDs called tags are inserted into Ethernet frames, can be used to configure multiple VLANs on one port.

VLAN tags use the trunk port. In addition to the opposing switch, trunk ports must also recognize VLAN tags.

In addition, the Switch supports frames with up to two VLAN Tag stages. Frames may not be relayed correctly if they are 3 or more stages.

(2) Protocol Specifications

VLAN tags can embed an ID called a tag into an Ethernet frame. These tags are used to report VLAN information (a VLAN ID) to separate segments.

The figure below shows the tagged-frame format. There are two formats for Ethernet frames into which VLAN tag are inserted: Ethernet V2 and 802.3.

Figure 24-2 Tagged frame format

The following table describes the fields for VLAN tags.

Table 24-5 VLAN Tag field
field	Description	Conditions for the Switch
TPID (Tag Protocol ID)	An Ether Type value indicating that the IEEE 802.1Q VLAN tag continues	Any value can be set for a port.
User Priority	Indicates the IEEE 802.1D priority.	Eight priority levels can be selected for configuration.
CF (Canonical Format)	Indicates whether the MAC address in the MAC header follows a standard format.	The Switch supports only standard (0) formats.
VLAN ID	Indicates an VLAN ID. ^#	VLAN ID that can be used by the user is 1 to 4094.

#

When Tag translation is used, VLAN ID set in Tag translation is used. For more information, see the description of 25.3 Tag transformations. When VLAN ID=0 is received, it is handled the same way as an untagged frame. VLAN ID=0 cannot be sent.

If the Switch grants a new VLAN Tag, User Priority defaults to 3.