QinQ vs. VLAN vs. VXLAN

VLAN (virtual local area network) technology removes distance and physical location restrictions, streamlining network management. However, as the number of devices and users grows in large-scale networks, VLAN faces limitations with a maximum of 4094 VLANs and inefficient network link utilization. To overcome these challenges, VXLAN (virtual extensible LAN) and QinQ technologies have emerged. This article will illustrate and compare these three technologies. In this article, these three technologies, QinQ vs. VLAN vs. VXLAN, will be illustrated and compared.

Overview of VLAN, VXLAN, and QinQ

What is VLAN (Virtual LAN)?

VLAN is a technology that divides a network into multiple broadcast domains. Within each broadcast domain, users can communicate freely. When it comes to establishing connections between distinct VLANs, there are two fundamental concepts to grasp: VLAN tagging and inter-VLAN routing.

VLAN tagging involves adding a unique identifier to frames as they pass through VLAN trunk ports, allowing frames from different VLANs to pass through. One of the methods for tagging is IEEE 802.1Q. Configuring VLANs is straightforward and user-friendly, both through CLI (Command Line Interface) and web-based user interfaces.

What is QinQ（802.1Q-in-802.1Q)？

QinQ, also referred to as VLAN stacking or double VLAN, is standardized under IEEE 802.1ad. It involves encapsulating the VLAN tag with dual layers—a private network's inner tag and a public network's outer tag. Q-in-Q is widely used in carrier backbone networks. By wrapping the VLAN tag of a private network within the VLAN tag of a public network, QinQ allows dual-VLAN-tagged packets to navigate through a carrier's backbone network (which is the public network). This mechanism expands the available VLAN capacity and facilitates more precise user management.

The IEEE 802.1Q standard specifies a 12-bit VLAN ID field that allows up to 4096 VLANs to be identified. However, as networks continue to expand, this limitation has become increasingly restrictive. In response, IEEE 802.1ad, an extension of the 802.1Q standard, introduces an additional 802.1Q tag (referred to as a VLAN tag) to packets originally tagged with 802.1Q. This innovation expands the potential number of VLANs to 4094 x 4094. Such dual-tagged packets are referred to as QinQ packets.

QinQ packets follow a standardized structure. Typically, an 802.1Q tagged packet is nested within an additional 802.1Q tag, hence the term "QinQ". As packets traverse the network, they are routed within the public network based on the outer VLAN tag. The inner VLAN tag is treated as data and traverses the public network along with it. This dual-tag configuration causes QinQ packets to have an additional four bytes compared to standard 802.1Q VLAN-tagged packets.

There are two main types of QinQ implementations: Basic QinQ and Selective QinQ.

Basic QinQ uses a port-based tagging approach. When a packet arrives at an interface with VLAN VPN enabled, the switch tags the packet with its default VLAN tag. Whether the incoming packet is already tagged or not, the result is the same. If it's already tagged, it will possess dual VLAN tags; if not, it will have a VLAN tag with the switch port.

Selective QinQ includes the capabilities of basic QinQ while introducing a higher level of flexibility. It identifies the inner VLAN tag of a packet based on the MAC address, IP protocol, source IP address, and VLAN tag, and then determines which tag should be added.

What is VXLAN (Virtual Extensible LAN)?

VXLAN, also known as Virtual Extensible LAN, is a technology that enables Layer 2 overlay networks to be built on top of a Layer 3 network using MAC address-in-user datagram protocol (MAC-in-UDP) encapsulation. In the data center, VXLAN is emerging as the dominant protocol for creating overlay networks that sit on top of the physical network, facilitating the implementation of virtual networks. By leveraging the VXLAN protocol, data center networks can be effectively virtualized while meeting the needs of multi-tenant data centers by providing extensive segmentation capabilities at scale. In essence, VXLAN provides similar services to VLAN, but with enhanced extensibility and flexibility. Like QinQ, VXLAN packets follow a consistent format. Using VXLAN MAC-in-UDP encapsulation, the original packets are provided with a VXLAN header and then placed inside a UDP IP packet. Here's a simple diagram to illustrate the concept.