dot1q command is used to configure Q-in-Q termination on a subinterface. The command accepts an Outer VLAN ID and one or more Inner
VLAN IDs. The outer VLAN ID always has a specific value, while inner VLAN ID can either be a specific value or a range of
A subinterface that is configured with a single Inner VLAN ID is called an unambiguous Q-in-Q subinterface. In the following
example, Q-in-Q traffic with an Outer VLAN ID of 101 and an Inner VLAN ID of 1001 is mapped to the Gigabit Ethernet 1/1/0.100
Device(config)# interface gigabitEehernet1/1/0.100
Device(config-subif)# encapsulation dot1q 101 second-dot1q 1001
A subinterface that is configured with multiple Inner VLAN IDs is called an ambiguous Q-in-Q subinterface. By allowing multiple
Inner VLAN IDs to be grouped together, ambiguous Q-in-Q subinterfaces allow for a smaller configuration, improved memory usage
and better scalability.
In the following example, Q-in-Q traffic with an Outer VLAN ID of 101 and Inner VLAN IDs anywhere in the 2001-2100 and 3001-3100
range is mapped to the Gigabit Ethernet 1/1/0.101 subinterface:
Device(config)# interface gigabitethernet1/1/0.101
Device(config-subif)# encapsulation dot1q 101 second-dot1q 2001-2100,3001-3100
Ambiguous subinterfaces can also use the
any keyword to specify the inner VLAN ID.
See the Configuration Examples for IEEE 802.1Q-in-Q VLAN Tag Termination section for an example of how VLAN IDs are assigned
to subinterfaces, and for a detailed example of how the
any keyword is used on ambiguous subinterfaces.
Only PPPoE is supported on ambiguous subinterfaces. Standard IP routing is not supported on ambiguous subinterfaces.