Qtech QSW-2900-24T-AC [82/209] Implementations of qinq

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· Provides a simple Layer 2 VPN solution for small-sized MANs or intranets.

Note: The QinQ feature requires configurations only on the service provider network, and

not on the customer network.

4.13.3 Implementations of QinQ

There are two types of QinQ implementations: basic QinQ and selective QinQ.

1) Basic QinQ

Basic QinQ is a port-based feature, which is implemented through VLAN VPN.

With the VLAN VPN feature enabled on a port, when a frame arrives at the port, the port will tag it with the

port’s default VLAN tag, regardless of whether the frame is tagged or untagged. If the received frame is already

tagged, this frame becomes a double-tagged frame; if it is an untagged frame, it is tagged with the port’s default

VLAN tag.

2) Selective QinQ

Selective QinQ is a more flexible, VLAN-based implementation of QinQ

4.13.4 Adjustable TPID Value of QinQ Frames

A VLAN tag uses the tag protocol identifier (TPID) field to identify the protocol type of the tag. The value of

this field, as defined in IEEE 802.1Q, is 0x8100.

Figure 2 shows the 802.1Q-defined tag structure of an Ethernet frame.

Figure 2 VLAN Tag structure of an Ethernet frame

On devices of different vendors, the TPID of the outer VLAN tag of QinQ frames may have different

default values. You can set and/or modify this TPID value, so that the QinQ frames, when arriving at the public

network, carries the TPID value of a specific vendor to allow interoperation with devices of that vendor.

The TPID in an Ethernet frame has the same position with the protocol type field in a frame without a

VLAN tag. To avoid chaotic packet forwarding and receiving, you cannot set the TPID value to any of the values in

the table below.

Table 1 Reserved protocol type values

Protocol type Value

ARP 0x0806

PUP 0x0200

RARP 0x8035

IP 0x0800

IPv6 0x86DD

PPPoE 0x8863/0x8864

MPLS 0x8847/0x8848