Quanta Cloud Technology QuantaMesh QNOS5, Configuration Manual

Page: 59 / 256

59
the switch can differentiate between customers in the MAN while preserving an individual customer’s VLAN
identification when the traffic enters the customer’s 802.1Q domain.
With the introduction of this second tag, customers are no longer required to divide the 4-byte VLAN ID
space to send traffic on a Ethernet-based MAN. In short, every frame that is transmitted from an interface has
a double- VLAN tag attached, while every packet that is received from an interface has a tag removed (if one
or more tags are present).
In Figure 2, two customers share the same metro core. The service provider assigns each customer a unique
ID so that the provider can distinguish between the two customers and apply different rules to each. When
the configurable EtherType is assigned to something different than the 802.1Q (0x8100) EtherType, it allows
the traffic to have added security from misconfiguration while exiting the metro core. For example, if the edge
device on the other side of the metro core is not stripping the second tag, the packet would never be
classified as a 802.1Q tag, so the packet would be dropped rather than forwarded in the incorrect VLAN.
Figure 3-2: Double VLAN Tagging Network Example
3.1.3. Default VLAN Behavior
One VLAN exists on the switch by default. The VLAN ID is 1, and all ports are included in the VLAN as access
ports, which are untagged. This means when a device connects to any port on the switch, the port forwards
the packets without inserting a VLAN tag. If a device sends a tagged frame to a port, the frame is dropped.
Since all ports are members of this VLAN, all ports are in the same broadcast domain and receive all
broadcast and multicast traffic received on any port.
When you add a new VLAN to the VLAN database, no ports are members. The configurable VLAN range is 2–
4093. VLANs 4094 and 4095 are reserved.
Table 1 shows the default values or maximum values for VLAN features.