Core issue
Encapsulating IEEE 802.1Q VLAN tags within 802.1Q enables service providers to use a single VLAN to support customers who have multiple VLANs. The IEEE 802.1 QinQ VLAN Tag Termination feature on the subinterface level preserves VLAN IDs and keeps traffic in different customer VLANs segregated.
Some ambiguous subinterfaces can use the any keyword for the inner VLAN ID specification. The any keyword represents any inner VLAN ID that is not explicitly configured on any other interface. In the following example, seven subinterfaces are configured with various outer and inner VLAN IDs.
The any keyword can be configured on only one subinterface of a specified physical interface and outer VLAN ID.
The encapsulation dot1q second-dot1q any command is supported only on a subinterface configured for Layer 2 (Ethernet over multiprotocol label switching [EoMPLS]) tunneling. If you use the encapsulation dot1q second-dot1q any command on a subinterface not configured for EoMPLS tunneling, all incoming packets are dropped without generating an error message.
Resolution
The any keyword in the second-dot1q command is supported only for Point-to-Point Protocol over Ethernet (PPPoE) QinQ traffic.
It is not supported on a subinterface configured for IP over QinQ because IP routing is not supported on ambiguous subinterfaces. Therefore, multiple values and ranges for the inner VLAN ID are not supported on IP over QinQ.
For more information, refer to PPPoE - QinQ Support.
