Tag Attributes

In a virtual LAN, the tag attribute of an Ethernet port indicates how the port processes Ethernet packets.

Ethernet packets are classified into tagged and untagged packets in 802.1q. A four-byte field is added to the Ethernet frame header of a tagged packet. The 802.1q-compliant field is used to identify the VLAN ID. An untagged packet does not have such field.

The tag attributes of the Ethernet port are classified into Tag aware, Access and Hybrid.

See Table 1 for details on how an Ethernet board processes tagged and untagged packets at the ingress.

**Table 1** Processing policy at ingress
Port Type	Tagged Packet	Untagged Packet
Tag aware	Transparently transmitted	Discarded
Access	Discarded	Added with the default VLAN tag
Hybrid	Transparently transmitted	Added with the default VLAN tag

See Table 2 for details on how an Ethernet board processes tagged and untagged packets at the egress.

**Table 2** Processing policy at egress
Port Type	Tagged Packet	Untagged Packet
Tag aware	Transparently transmitted	-
Access	The VLAN tag is removed	-
Hybrid	The VLAN tag is removed if it is the same as the default tag for the port Transparently transmitted if the VLAN tag is different from the default tag for the port	-

As shown in Table 1 and Table 2, in an actual network, you need to set the port type for the Ethernet board of an NE according to the Tag attribute of the messages sent from the user-side equipment.

If the user-side equipment sends the Untag message, set the external port to Access and set the internal port to Tag aware.
If the user-side equipment sends the Tag message, set the external port to Tag aware and set the internal port to Tag aware.

For example, if the source equipment of a service does not support Tag messages but the sink equipment supports Tag messages, you need to set the external port of the Ethernet board that resides on the NE connected to the source to Access, and set the external port of the Ethernet board that resides on the NE connected to the sink to Tag aware. Set the internal ports of the Ethernet boards that reside on the NEs connected to the source and the sink to Tag aware.