Which two statements describe primary differences between MPLS Layer 2 and Layer 3 VPNs? (Choose two.)

Question

Options

• ALayer 2 VPNs use IPsec tunneling, but Layer 3 VPNs use L2TPv3 tunneling.
• BLayer 2 VPNs use AToM, but Layer 3 VPNs use MPLS/BGP.
• CLayer 2 VPNs use BGP, but Layer 3 VPNs use VPLS.
• DLayer 2 VPNs use L2TPv3 tunneling, but Layer 3 VPNs use GRE tunneling.
• ELayer 2 VPNs use IPsec tunneling, but Layer 3 VPNs use pseudowires to provide tunneling.

• A
  18% (7)
• B
  70% (28)
• C
  8% (3)
• E
  5% (2)

Explanation

B is correct because AToM (Any Transport over MPLS) is the Cisco technology for Layer 2 VPNs - it uses pseudowires to carry L2 frames (Ethernet, Frame Relay, ATM) across an MPLS backbone without the provider participating in customer routing. MPLS/BGP (RFC 4364) is the standard Layer 3 VPN mechanism, where Provider Edge (PE) routers use BGP to exchange customer routes and VRFs to maintain per-customer routing tables.

D is correct because L2TPv3 (Layer 2 Tunneling Protocol version 3) is designed specifically to tunnel Layer 2 frames over IP networks, making it a Layer 2 VPN transport. GRE (Generic Routing Encapsulation) is a generic Layer 3 tunneling mechanism used in L3 VPN scenarios when MPLS isn't available end-to-end.

Why the distractors fail:

• A & E: IPsec is an encryption framework, not a Layer 2-specific tunneling technology - it applies to many VPN types. E also misplaces pseudowires, which belong to L2 (AToM), not L3.
• C: This reverses the correct mapping - BGP belongs to L3 VPNs (MPLS/BGP), and VPLS (Virtual Private LAN Service) is a multipoint Layer 2 VPN technology.

Memory tip: Match the numbers - L2TPv3 has "L2" in the name (Layer 2 VPN), and AToM = "Any Transport over MPLS" = L2 frames riding MPLS. For L3 VPNs, think BGP = Big routing tables shared between provider routers.

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