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.

(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 formats

The following table describes the fields for VLAN tags.

Table 24-5: VLAN Tag fields
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, the VLAN ID set for 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.

The Switch uses the same user priority for frames forwarded by Layer 2 that are used for received frames. If a received frame is untagged, the user priority is the default value of 3. Also, the user priority for sent frames can be changed by configuration. For details about changing User Priority and User Priority of frames forwarded by the Switch at Layer 3, see the Configuration Guide Vol.2" "3.7 Marker Description.