Overview QinQ and VLAN Mapping

802.1Q in 802.1Q (QinQ), which is an extension of the 802.1Q protocol, adds a layer of 802.1Q tag (VLAN tag) on the basis of the original 802.1Q packet header. By use of two layers of VLAN tags, the number of VLANs is increased to 4094x4094. QinQ encapsulates user private network VLAN tags into public network VLAN tags so that the packets are transmitted in the carrier backbone network (public network) with two layers of VLAN tags. In the public network, the packets are broadcasted based on the outer VLAN tags (that is, public network VLAN tags), and the user private network VLAN tags are shielded. This saves public network VLAN IDs, and provides a simple L2 Virtual Private Network (VPN) tunnels for users.

According to rules of adding VLAN tags, QinQ falls into the following types:

• Basic QinQ
• Port-based flexible QinQ

VLAN mapping is also an extension of 802.1Q. It is different from QinQ in the following aspect: Instead of encapsulating another layer of VLAN tag on the basis of the original VLAN tag of a packet, VLAN mapping replaces the original VLAN tag of a packet with a new VLAN tag. In this way, the packet still has only one layer of VLAN tag.

According to the mapping rules, VLAN mapping falls into the following types:

• 1:1 VLAN mapping. Only one private network VLAN can be mapped into one public network VLAN.
• N:1 VLAN mapping. That is, one or more private VLANs can be mapped to a public VLAN.

For port-based flexible QinQ, 1:1 VLAN mapping, private network VLAN to public network VLAN mapping entries must be configured. A user can configure a maximum of 4096 mapping entries.