350-401 Question #1137: Real Exam Question with Answer & Explanation

Question

Which device, in a LISP router architecture, receives LISP map requests and determines which ETR should handle the map request?

Options

• Aproxy ETR
• Brouting locator
• Cmap resolver
• Dmap server

Explanation

LISP Map Resolver Explained

A Map Resolver (MR) is the LISP device that receives Map-Request messages from ITRs (Ingress Tunnel Routers) and determines which ETR (Egress Tunnel Router) is authoritative for a given EID (Endpoint Identifier), forwarding the request accordingly - making C correct.

A Map Server (D) is closely related but plays the opposite role: it receives Map-Register messages from ETRs to store EID-to-RLOC mappings, not to resolve incoming requests. A Proxy ETR (A) acts as a substitute ETR to handle traffic on behalf of LISP sites that cannot be reached directly, which is a forwarding function, not a mapping resolution function. A Routing Locator (B) is simply an IP address used to locate a LISP router in the underlay network - it's a data element, not a device.

🧠 Memory Tip: Think of it like DNS - the Map Resolver = a DNS resolver (asks the question and finds who knows the answer), while the Map Server = a DNS authoritative server (stores and registers the answers).

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