Refer to the Exhibit. In which three Layers should you use nonstop Forwarding to reduce service impact in case of failure? (Choose three)

Question

Exhibit

Options

• AEnterprise Edge
• BEnterprise Core
• CService provider Edge
• DDual-attached sever Layer
• EEnterprise Non-Routed Access Layer
• FEnterprise Non-Routed Distribution Layer.

Explanation

Nonstop Forwarding (NSF) - Correct Answer: A, B, C

NSF belongs in the three routed layers - Enterprise Edge (A), Enterprise Core (B), and Service Provider Edge (C) - because NSF is a control-plane resilience feature that only has value where Layer 3 routing protocols (OSPF, BGP, EIGRP, IS-IS) are actively running. When a supervisor or routing process fails, NSF allows the data plane to keep forwarding packets using cached routes while the routing process restarts, preventing traffic outages in high-throughput, routed segments.

Why the distractors are wrong:

• D (Dual-attached Server Layer) - typically a Layer 2 access construct; servers connect via port channels or bonded NICs, not routed adjacencies, so NSF offers no benefit.
• E (Enterprise Non-Routed Access Layer) - the word Non-Routed is the giveaway; it operates at Layer 2, so there are no routing adjacencies to preserve.
• F (Enterprise Non-Routed Distribution Layer) - same reasoning as E; without Layer 3 routing, NSF has nothing to protect.

Memory tip: The key phrase is "Non-Routed" - any layer with that label in the answer choices is automatically eliminated from NSF consideration. NSF = routing protocols = routed layers only. Think: "NSF lives where routes live."

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