It is important to understand the next generation networks and the one of the term you always heard is VXLAN. Let's talk about these two terms QinQ and VXLAN.

IEEE 802.1ad standardizes QinQ, also known as stacking VLAN or double VLAN.VLAN tags are encapsulated in two layers. Private networks have an inner tag and public networks have an outer tag.

The traditional VLAN tagging that uses IEEE 802.1Q is unable to identify and isolate users' data as there are more users in networks, which require large numbers of VLANs IDs. Therefore, QinQ is used to extend the VLAN numbers up to 4096×4096, which can save public VLAN IDs effectively.

Fig 1.1- QinQ

There is a fixed format for QinQ packets. The name "QinQ" comes from the fact that an 802.11Q tagged packet is usually enclosed in another 802.1Q tag. As packets are transmitted over the public network, they are forwarded based on their outer VLAN tags.

Data transmitted through the public network is also taken into account as the inner VLAN tag. QinQ packets have four more bytes with this double tagged form than typical 802.1Q VLAN tagged packets.

There are two kinds of QinQ implementations and these are basic QinQ and selective QinQ.

Basic QinQ
Basic QinQ is a tagging way based on port. When a packet arrives at the interface that has VLAN VPN enabled, the switch will tag the packet with its default VLAN tag. It doesn’t matter whether the incoming packet is tagged or not. If it has been tagged, then it will have double VLAN tags; if not, it will have a single VLAN tag with the switch port.

Selective QinQ
Selective QinQ Selective QinQ owns the functions of basic QinQ, but it is more flexible. It can identify the inner VLAN tag of the packets according to the MAC address, IP protocol, source IP address and VLAN tag, then determine which tag it should be added.

VXLAN(Virtual Extensible Local Area Network)
As with VLAN today, VXLAN is designed to provide the same Ethernet Level 2 services as VLAN, but with greater extensibility and flexibility. In a large multitenant environment, VXLAN provides a flexible, multitenant solution over a shared physical infrastructure. It operates by using IP plus UDP to travel over the physical network.

VXLAN enables tenant workloads to be distributed across multiple physical pods in the datacenter by extending Layer 2 segments over shared network infrastructure.

Fig 1.2- VXLAN

VXLAN uses a 24-bit segment ID known as the VXLAN network identifier (VNID), which enables up to 16 million VXLAN segments to coexist in the same administrative domain.

VXLAN packets are transferred through the underlying network based on its Layer 3 header and can take complete advantage of Layer 3 routing, equal-cost multipath (ECMP) routing, and link aggregation protocols to use all available paths.

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