300-320 Question #360: Real Exam Question with Answer & Explanation

The correct answer is C: They support only IP traffic. MPLS Layer 3 VPNs are designed exclusively around IP routing-PE routers exchange VPNv4 routes via MP-BGP and forward traffic using IP lookups with MPLS labels. They cannot natively transport non-IP legacy protocols (such as IPX or SNA), which is a key limitation (C). Choice A is

Question

What is one limitation of MPLS Layer 3 VPN networks?

Options

AThey require less powerful routers with limited capabilities
BThey require the customer to control routing
CThey support only IP traffic
DPE routers are underutilized

Explanation

MPLS Layer 3 VPNs are designed exclusively around IP routing-PE routers exchange VPNv4 routes via MP-BGP and forward traffic using IP lookups with MPLS labels. They cannot natively transport non-IP legacy protocols (such as IPX or SNA), which is a key limitation (C). Choice A is incorrect because MPLS L3 VPN actually demands more powerful routers (PE routers must handle label imposition, VRF routing tables, and MP-BGP). Choice B is wrong because in MPLS L3 VPN, the service provider's PE routers manage routing transparently-the customer does not need to control it. Choice D is incorrect because PE routers in MPLS environments are heavily utilized, maintaining per-VRF routing tables and handling label operations.

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