Regarding QinQ VLAN, which of the following statements are correct?

Question

Options

• AMeet the needs of private network VLAN users for point-to-point private line interconnection
• BQinQ VLAN corresponds to a routing interface
• CDuring the transmission of the metropolitan area network, the upper device only needs to identify
• DThe main purpose of QinQ VLAN is to save IP addresses.

• A
  81% (35)
• B
  12% (5)
• D
  7% (3)

Explanation

Option A is correct because QinQ (IEEE 802.1ad double tagging) was specifically designed to allow enterprise or private network customers to extend their VLANs transparently across a metropolitan area network, effectively simulating point-to-point private line connectivity between sites. Option C is correct because in a QinQ architecture, service provider (metro) devices only need to read and switch on the outer VLAN tag (the S-tag); the inner customer VLAN tag (C-tag) is carried transparently and untouched through the provider network, which greatly simplifies provider operations.

Option B is wrong because QinQ operates at Layer 2 and is purely a tunneling/tagging mechanism; it does not inherently correspond to a Layer 3 routing interface (that concept applies to SVIs on standard VLANs). Option D is wrong because saving IP addresses is the purpose of NAT, not QinQ; QinQ's primary goals are expanding usable VLAN ID space (from 4,096 to over 16 million combinations) and enabling transparent customer VLAN transport.

Memory tip: Think of QinQ as an envelope inside an envelope - the postal carrier (metro network) only reads the outer envelope address (outer VLAN tag) to deliver it, never opening the inner envelope (customer VLAN tag), which is what makes transparent private-line interconnection possible.

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