Exam 350-401 topic 1 question 705 discussion

Passed My Exam on 15th , 100% From here, Three Labs GLBP, BGP R1 R3, Netflow IP Sla.

An ITR is responsible for finding EID-to-RLOC mappings for all traffic destined for LISP-capable sites. When the ITR receives a packet destined for an EID, it first looks for the EID in its mapping cache. If the ITR finds a match, it encapsulates the packet inside a LISP header with one of its RLOCs as the IP source address and one of the RLOCs from the mapping cache entry as the IP destination. The ITR then routes the packet normally.

The key to this question is that you need to understand how the EID-to-RLOC mapping is discovered. The device responsible for receiving mapping requests (Map-Requests) and responding with the appropriate RLOC mapping is the Map Resolver. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_lisp/configuration/15-sy/irl-15-sy-book/irl-overview.html

It's A: MR receives map-requests from ITRs and forwards them to the appropriate Map Server or ETR to obtain the EID-to-RLOC mapping. It's not D, because Ingress Tunnel Router encapsulates traffic but relies on MR for mappings.

A was my answer. I afterwards asked copilot and deepseek and they both said A

It's the wording again, they are not asking where the mapping record is kept or the interface to query the mapping , the question is : "What device is responsible for finding the mapping" , so when there is a need to find it ? When ITR receives a transmission , subsequently it's responsible for finding because it's the ITR that would then use it to relay it to ETR. Just my two cents. The answer is D. Always be careful with the way CISCO have the question composed.

I think the correct answer is MS/MR. It is a device that combines the capabilities of MSs (map-servers) & MRs (map-resolvers). Since we can't use one without the other, I will go with 'D.' ITR finds the right RLOC by sending a map request to the MS through MR. MS delivers the map-request message to the appropriate ETR to learn its corresponding RLOC, and then the ETR @ destination sends back RLOC, for the destined host, in a "map-reply" response to the ITR @ source location.

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_lisp/configuration/15-mt/irl-15-mt-book/irl-overview.pdf

An ITR is responsible for finding EID-to-RLOC mappings for all traffic destined for LISP-capable sites.

another broken question, one word changes question's whole meaning.

An ETR connects a site to the LISP-capable part of a core network (such as the Internet), publishes EID-to-RLOC mappings for the site, responds to Map-Request messages, and decapsulates and delivers LISP-encapsulated user data to end systems at the site

Responsible means to search for RLOC and route the traffic in time. So D.

Answer is D https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_lisp/configuration/15-mt/irl-15-mt-book/irl-overview.pdf Thank god for discussions or I will fail lol

D - read the working of the question.

chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_lisp/configuration/xe-3s/irl-xe-3s-book/irl-overview.pdf

Map server: This is a network device that learns EID-to-prefix mapping entries from an ETR and stores them in a local EID-to-RLOC mapping database. I think C is correct

I think the answer is D. An ITR is responsible for finding EID-to-RLOC mappings for all traffic destined for LISP-capable sites