IEEE 802.1ad is an Ethernet networking standard informally known as QinQ as an amendment to IEEE standard IEEE 802.1Q-1998 that was incorporated into the base 802.1Q standard in 2011. The technique is also known as provider bridging, Stacked VLANs.

802.1Q-in-802.1Q (QinQ) is a technology that addresses the shortage of public VLAN ID resources. This technology applies to a number of services in metropolitan area network (MAN) implementation.

QinQ Support on Layer 2 Ports. Customizable Tunneling MAC Address. Example: EoMPLS xconnect on SVI. Example: QinQ and L2PT on L2 ports with Dual-Homed Topology.

QinQ Overview. Simulated Network Topology. Device Summary. QinQ with OpenFlow. QinQ Tag Exclusivity. VLAN and QinQ VLAN on Same Port. Integration Tests.

HUAWEI S Series Switch-Configure QinQ.

Configuring Q-in-Q Tunneling on QFX Series Switches. Configuring Q-in-Q Tunneling on EX Series Switches with ELS Support. Configuring Q-in-Q Tunneling on EX Series Switches. Configuring Q-in-Q...

I find this Cisco 7600 series router config document regards to QinQ (802.1ad)

The QinQ technology is called VLAN dot1q tunnel, 802.1Q tunnel, VLAN Stacking technology. QinQ encapsulates the private network VLAN tag of the user in the public(service provider) network VLAN...

QinQ, or dot1q tunnels, are used by service providers to keep customer traffic separate at layer-2. Darren's Blog - Fun with QinQ. Packet Life - IEEE 802.1Q Tunneling.