How can a Layer 3 MPLS VPN provider support customers with an overlapping IP address space?

Question

Options

• AEach customer IP prefix is assigned a different RT value.
• BEach customer IP prefix is appended with a unique RD value.
• CEach customer route is injected into a separate GRE tunnel inside the MPSL core.
• DEach customer route is injected into a separate VPWS tunnel inside the MPSL core.

• B
  92% (22)
• C
  4% (1)
• D
  4% (1)

Explanation

A Route Distinguisher (RD) is a 64-bit value prepended to a customer's IPv4 prefix to create a globally unique 96-bit VPNv4 address (RD + 32-bit IPv4 = 96-bit VPNv4). This allows multiple customers using the same overlapping IP address space (e.g., 10.0.0.0/8) to coexist in the provider's MP-BGP table without conflict, because each customer's routes are distinguished by their unique RD. Option A confuses RD with RT (Route Target), which is used for route import/export policy between VRFs, not for making addresses unique. Options C and D (GRE and VPWS tunnels) are not how standard Layer 3 MPLS VPN handles address overlap - the VRF and RD mechanism handles it natively.

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