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Configuring QinQ
NOTE:
In this documentation, SPC cards refer to the cards prefixed with SPC, for example, SPC-GT48L, and SPE
cards refer to the cards prefixed with SPE, for example, SPE-1020-E-II.
Introduction to QinQ
802.1Q in 802.1Q (QinQ) is a flexible, easy-to-implement Layer 2 VPN technology based on IEEE
802.1Q. It enables the edge router on the service provider network to encapsulate an outer VLAN tag in
Ethernet frames from customer networks (private networks), so that the Ethernet frames will travel across
the service provider network (public network) with double VLAN tags. QinQ enables a service provider
to use a single provider network VLAN (SVLAN) to serve customers who have multiple customer network
VLANs (CVLANs).
Background and benefits
The IEEE 802.1Q VLAN tag uses 12 bits for VLAN IDs. A network device supports a maximum of 4094
VLANs, which is far from enough for isolating users in actual networks, especially in metropolitan area
networks (MANs).
By tagging tagged frames, QinQ expands the available VLAN space from 4094 to 4094 × 4094. QinQ
delivers the following benefits:
Releases the stress on the SVLAN resource.
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Enables customers to plan their CVLANs without conflicting with SVLANs.
Provides an easy-to-implement Layer 2 VPN solution for small-sized MANs or intranets.
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Allows the customers to keep their current network configurations when the service provider
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upgrades the service provider network, thus making the customer networks more independent.
How QinQ works
The devices in the public network forward a frame only according to its outer VLAN tag and learn its
source MAC address into the MAC address table of the outer VLAN. The inner VLAN tag of the frame is
transmitted as payload.
NOTE:
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All QinQ-related configurations are made on the service provider network only.
Because QinQ is based on the IEEE 802.1Q protocol, all network devices through which QinQ packets
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may pass must support the IEEE 802.1Q protocol.
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