300-320 Question #258: Real Exam Question with Answer & Explanation

The correct answer is A: MPLS. MPLS Layer 3 VPNs have three fundamental prerequisites on Cisco devices: (1) MPLS - the core label-switching infrastructure that forwards packets based on labels rather than IP lookups; (2) LDP (Label Distribution Protocol) - the protocol that distributes and negotiates label bin

Question

A designer should have which three technologies in the network before configuring MPLS Layer 3 VPNs? (Choose three.)

Options

AMPLS
BLDP
CCisco Express Forwarding
DVSS
EvPC
FVRRP

Explanation

MPLS Layer 3 VPNs have three fundamental prerequisites on Cisco devices: (1) MPLS - the core label-switching infrastructure that forwards packets based on labels rather than IP lookups; (2) LDP (Label Distribution Protocol) - the protocol that distributes and negotiates label bindings between MPLS-enabled routers so each router knows which label to use for each prefix; (3) Cisco Express Forwarding (CEF) - required on Cisco routers because MPLS depends on CEF for the FIB (Forwarding Information Base) and label imposition/disposition. Without CEF, MPLS cannot function on Cisco platforms. Options D (VSS - Virtual Switching System), E (vPC - virtual Port Channel), and F (VRRP - Virtual Router Redundancy Protocol) are all high-availability or chassis-virtualization technologies that have no dependency relationship with MPLS L3 VPN configuration.

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