Hybrid VLAN-based Layer 2 Protocol Tunneling Application

When each edge device interface on a backbone network connects to more than one user network and some Layer 2 protocol data units (PDUs) from the user networks carry VLAN tags while others do not, configure hybrid VLAN-based Layer 2 protocol tunneling to allow both the tagged and untagged Layer 2 PDUs from the user networks to be tunneled across the backbone network. Layer 2 PDUs from the user networks then travel through different Layer 2 tunnels to reach the destinations to perform Layer 2 protocol calculation.

In Figure 1, PEs on the backbone network edge must tunnel both tagged and untagged Layer 2 PDUs from a large number of VLAN users across the backbone network.

Figure 1 Hybrid VLAN-based Layer 2 protocol tunneling networking

PE1, PE2, and PE3 constitute a backbone network. LAN-A and LAN-C belong to VLAN 3; LAN-B and LAN-D belong to VLAN 2. All LANs send tagged Layer 2 PDUs. CE1 can forward Layer 2 PDUs carrying VLAN 2 and VLAN 3. CE2 can forward Layer 2 PDUs carrying VLAN 3. CE3 can forward Layer 2 PDUs carrying VLAN 2. CE1, CE2, and CE3 also run an untagged Layer 2 protocol, such as LLDP.

To tunnel both tagged and untagged Layer 2 PDUs from a large number of VLAN users across the backbone network, configure hybrid tagged and hybrid untagged attributes and enable both interface-based and VLAN-based Layer 2 protocol tunneling on the user-side interfaces of PE1, PE2, and PE3.

The Layer 2 protocol tunneling process is as follows:

PE1 receives tagged and untagged Layer 2 PDUs and adds the default VLAN ID of the interface that has received the untagged Layer 2 PDUs to these PDUs.
PE1 replaces the multicast destination MAC address in the Layer 2 PDUs with a specified multicast MAC address based on the configured mapping between the multicast destination MAC address and the specified multicast MAC address.
The internal devices on the backbone network forward the Layer 2 PDUs with a specified multicast MAC address to the egress devices.
The egress devices PE2 and PE3 restore the original destination MAC address in the Layer 2 PDUs based on the configured mapping between the multicast destination MAC address and the specified multicast address. They also remove the outer VLAN tags and send the Layer 2 PDUs to the user networks.