QinQ Tunneling

Last Updated on Sun, 06 Aug 2023 | Routing and Switching

Traditionally, VLANs have not extended beyond the WAN boundary. VLANs in one campus extend to a WAN edge router, but VLAN protocols are not used on the WAN.

Today, several emerging alternatives exist for the passage of VLAN traffic across a WAN, including 802.1Q-in-Q, Ethernet over MPLS (EoMPLS), and VLAN MPLS (VMPLS). While these topics are more applicable to the CCIE Service Provider certification, you should at least know the concept of 802.1 Q-in-Q tunneling.

Also known as Q-in-Q or Layer 2 protocol tunneling, 802.1Q-in-Q allows an SP to preserve 802.1Q VLAN tags across a WAN service. By doing so, VLANs actually span multiple geographically dispersed sites. Figure 2-5 shows the basic idea.

Figure 2-5 Q-in-Q: Basic Operation

KEY POINT

Customerl: VLAN 5 Customerl: VLAN 6

Eth.

VLAN

Data

Header

ID 100

Eth.

VLAN

Data

Header

ID 100

Eth.

VLAN

VLAN

Data

Header

ID 5

ID 100

Eth.

VLAN

VLAN

Data

C2-SW1 Y

Header

ID 6

VLANs 100-500

Eth.

VLAN

Data

Header

ID 100

Eth.

VLAN

Data

Header

ID 100

The ingress SP switch takes the 802.1Q frame, and then tags each frame entering the interface with an additional 802.1Q header. In this case, all of Customer1's frames are tagged as VLAN 5 as they pass over the WAN; Customer2's frames are tagged with VLAN 6. After removing the tag at egress, the customer switch sees the original 802.1Q frame, and can interpret the VLAN ID correctly. The receiving SP switch (SP-SW2 in this case) can keep the various customers' traffic separate based on the additional VLAN tags.

Using Q-in-Q, an SP can offer VLAN services, even when the customers use overlapping VLAN IDs. Customers get more flexibility for network design options, particularly with metro Ethernet services. Plus, CDP and VTP traffic passes transparently over the Q-in-Q service.

Continue reading here: PerVLAN Spanning Tree and STP over Trunks

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Readers' Questions

  • kaarlo
    Why qinq tunneling is used?
    4 months ago
    • QinQ tunneling is used to extend VLANs across a Layer 2 network. It enables multiple VLANs to be mapped to a single VLAN on the trunk port, allowing the extended VLANs to be transported over long distances without the need for manual configuration of each VLAN at both ends of the link. This helps to reduce the complexity of managing multiple Layer 2 segments across different sites.