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What is Double Tagging (QinQ)? An easy-to-understand explanation of the basic concepts of network technology
Network technology is a complex field that requires a deep understanding of various protocols and techniques. One such technique is Double Tagging, also known as QinQ. In this blog post, we will explore what Double Tagging (QinQ) is and how it works in a simple and concise manner.
Understanding VLANs
Before diving into Double Tagging, it is essential to comprehend the concept of Virtual Local Area Networks (VLANs). VLANs allow network administrators to segregate a physical network into multiple logical networks. Each VLAN acts as a separate broadcast domain, enhancing security and manageability.
Introducing Double Tagging (QinQ)
Double Tagging, or QinQ (short for “double VLAN tagging”), is a technique that extends the capabilities of VLANs. It enables service providers to provide VLAN services to their customers while efficiently utilizing their existing infrastructure.
The basic idea behind Double Tagging is to encapsulate VLAN-tagged packets within another set of VLAN tags. This process adds an additional layer of VLAN tags to the original packet, hence the “double tagging” terminology.
By using Double Tagging, service providers can deliver VLAN services to multiple customers over a shared network infrastructure. Each customer’s traffic is distinguished by the outer VLAN tag, while the inner VLAN tag helps differentiate the VLANs within the customer’s network.
How Double Tagging (QinQ) Works
Let’s walk through a simplified example to understand how Double Tagging works in practice.
Suppose a service provider needs to deliver VLAN services to two customers, A and B, over their existing network infrastructure. Customer A requires VLAN 10, and Customer B requires VLAN 20.
1. The service provider assigns unique outer VLAN tags to each customer’s traffic. For example, they assign VLAN tag 100 for Customer A and VLAN tag 200 for Customer B.
2. When Customer A sends a packet with VLAN tag 10, the service provider adds the outer VLAN tag 100 to the packet. This effectively creates a “QinQ” packet with two VLAN tags: 100 (outer) and 10 (inner).
3. The service provider’s network infrastructure recognizes the outer VLAN tag (100) and forwards the packet to the appropriate destination (Customer A’s VLAN).
4. Similarly, when Customer B sends a packet with VLAN tag 20, the service provider adds the outer VLAN tag 200 to the packet, resulting in a “QinQ” packet with VLAN tags 200 (outer) and 20 (inner).
5. The service provider’s network infrastructure uses the outer VLAN tag (200) to route the packet to the correct destination (Customer B’s VLAN).
By using Double Tagging, service providers effectively create “sub-VLANs” within their infrastructure, allowing multiple customers to enjoy VLAN services without the need for dedicated physical resources for each customer.
Conclusion
Double Tagging (QinQ) is a powerful technique that enables service providers to deliver VLAN services to multiple customers efficiently. By understanding the basic concepts of VLANs and Double Tagging, network administrators can make informed decisions on network design and management.
In this blog post, we have provided an easy-to-understand explanation of Double Tagging (QinQ) and its working principles. By leveraging this technique, network professionals can optimize their infrastructure and provide enhanced services to their customers.
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