350-401 Question #849: Real Exam Question with Answer & Explanation

Question

Which LISP component decapsulates messages and forwards them to the map server responsible for the egress tunnel routers?

Options

• ARouter Locator
• BMap Resolver
• CProxy ETR
• DIngress Tunnel Router

Explanation

LISP Map Resolver Explanation

Map Resolver (B) is correct because it is the LISP component that receives encapsulated Map-Request messages from Ingress Tunnel Routers (ITRs), decapsulates them, and then forwards those requests to the appropriate Map Server that holds the mapping information for the destination Egress Tunnel Router (ETR).

Why the distractors are wrong:

• Router Locator (A) is not a standard LISP component - LISP uses "RLOCs" (Routing Locators) as addresses, not a device called a Router Locator, making this a fabricated distractor.
• Proxy ETR (C) handles traffic on behalf of non-LISP sites by receiving and forwarding data packets - it does not process Map-Requests or interact with the Map Server in this way.
• Ingress Tunnel Router (D) is the device that sends the encapsulated Map-Request to the Map Resolver - it initiates the lookup process rather than decapsulating and forwarding it.

Memory Tip: Think of the Map Resolver as a "postal sorting facility" - it receives the encapsulated request, opens (decapsulates) it, and routes it to the correct Map Server, just like a mail sorter forwards your letter to the right destination post office.

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