**Overview**

IEEE 802.1ad_, commonly known as QinQ, is an Ethernet standard first published 
as an amendment to 802.1q_ in 2005, then officially merged into the base 
standard in 2011.

Unlike the original 802.1q_, which allows a single VLAN header per Ethernet 
frame, QinQ allows two VLAN headers per Ethernet frame, for the inner and the outer VLAN tags.
Most often the inner VLAN tag comes from a customer while the outer tag is used by the service
provider to differentiate between traffic of different customers.


**Frame structure and ethertypes**

The IEEE 802.1ad_ (QinQ) frame includes two VLAN tags:

* **The outer service tag (S-TAG):** The S-TAG is typically added by the provider.
It uses the Ethertype 0x88a8 by default. 

* **The inner customer tag (C-TAG):** The C-TAG is generated by the customer's equipment and 
  remains unchanged during transit. It uses the Ethertype 0x8100.

**Implementation in VyOS**

In VyOS, these tag types are associated with the following CLI options:

* ``vif-s``: Corresponds to the S-TAG (Ethertype 0x88a8).
* ``vif-c``: Corresponds to the C-TAG (Ethertype 0x8100).

.. cmdinclude:: /_include/interface-address-with-dhcp.txt
   :var0: {{ var0 }}
   :var1: {{ var1 }}
   :var2: vif-s
   :var3: <vlan-id>
   :var4: 1000
   :var5: vif-c
   :var6: <vlan-id>
   :var7: 20

.. cmdinclude:: /_include/interface-description.txt
   :var0: {{ var0 }}
   :var1: {{ var1 }}
   :var2: vif-s
   :var3: <vlan-id>
   :var4: 1000
   :var5: vif-c
   :var6: <vlan-id>
   :var7: 20

.. cmdinclude:: /_include/interface-disable.txt
   :var0: {{ var0 }}
   :var1: {{ var1 }}
   :var2: vif-s
   :var3: <vlan-id>
   :var4: 1000
   :var5: vif-c
   :var6: <vlan-id>
   :var7: 20

.. cmdinclude:: /_include/interface-disable-link-detect.txt
   :var0: {{ var0 }}
   :var1: {{ var1 }}
   :var2: vif-s
   :var3: <vlan-id>
   :var4: 1000
   :var5: vif-c
   :var6: <vlan-id>
   :var7: 20

.. cmdinclude:: /_include/interface-mac.txt
   :var0: {{ var0 }}
   :var1: {{ var1 }}
   :var2: vif-s
   :var3: <vlan-id>
   :var4: 1000
   :var5: vif-c
   :var6: <vlan-id>
   :var7: 20

.. cmdinclude:: /_include/interface-mtu.txt
   :var0: {{ var0 }}
   :var1: {{ var1 }}
   :var2: vif-s
   :var3: <vlan-id>
   :var4: 1000
   :var5: vif-c
   :var6: <vlan-id>
   :var7: 20

.. cmdinclude:: /_include/interface-ip.txt
   :var0: {{ var0 }}
   :var1: {{ var1 }}
   :var2: vif-s
   :var3: <vlan-id>
   :var4: 1000
   :var5: vif-c
   :var6: <vlan-id>
   :var7: 20

.. cmdinclude:: /_include/interface-ipv6.txt
   :var0: {{ var0 }}
   :var1: {{ var1 }}
   :var2: vif-s
   :var3: <vlan-id>
   :var4: 1000
   :var5: vif-c
   :var6: <vlan-id>
   :var7: 20

.. cmdinclude:: /_include/interface-vrf.txt
   :var0: {{ var0 }}
   :var1: {{ var1 }}
   :var2: vif-s
   :var3: <vlan-id>
   :var4: 1000
   :var5: vif-c
   :var6: <vlan-id>
   :var7: 20

**DHCP(v6)**

.. cmdinclude:: /_include/interface-dhcp-options.txt
   :var0: {{ var0 }}
   :var1: {{ var1 }}
   :var2: vif-s
   :var3: <vlan-id>
   :var4: 1000
   :var5: vif-c
   :var6: <vlan-id>
   :var7: 20

.. cmdinclude:: /_include/interface-dhcpv6-options.txt
   :var0: {{ var0 }}
   :var1: {{ var1 }}
   :var2: vif-s
   :var3: <vlan-id>
   :var4: 1000
   :var5: vif-c
   :var6: <vlan-id>
   :var7: 20

.. cmdinclude:: /_include/interface-dhcpv6-prefix-delegation.txt
   :var0: {{ var0 }}
   :var1: {{ var1 }}
   :var2: vif-s
   :var3: <vlan-id>
   :var4: 1000
   :var5: vif-c
   :var6: <vlan-id>
   :var7: 20

.. include:: /_include/common-references.txt