350-401 Question #1083: Real Exam Question with Answer & Explanation

Question

Which action is a LISP ITR responsible for?

Options

• Aresponding to map-request messages
• Bforwarding user data traffic
• Cfinding EID-to-RLOC mappings
• Daccepting registration requests from ETRs

Explanation

LISP ITR Responsibility

An Ingress Tunnel Router (ITR) is responsible for finding EID-to-RLOC mappings (Option C) because it receives traffic from internal hosts and must determine how to encapsulate and forward that traffic toward the correct destination - it does this by sending Map-Request messages to the mapping system to resolve Endpoint Identifiers (EIDs) to Routing Locators (RLOCs).

• Option A is wrong because responding to Map-Request messages is the job of the ETR (Egress Tunnel Router) or the Map-Server/Map-Resolver, not the ITR - the ITR sends Map-Requests, it doesn't answer them.
• Option B is wrong because simply "forwarding user data traffic" describes a basic router function; the ITR's defining role is the LISP-specific task of resolving mappings and encapsulating traffic, not generic forwarding.
• Option D is wrong because accepting registration requests from ETRs is the responsibility of the Map-Server, which stores and manages the mapping database.

🧠 Memory Tip: Think of ITR = Inquire - the ITR inquires (asks) for mappings. ETR = Enroll - the ETR enrolls (registers) with the Map-Server.

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