Which Device Finds EID-to-RLOC Mapping in LISP?
Explain the working principles of the Cisco SD-Access solution
Describe network virtualization concepts
Which device is responsible for finding EID-to-RLOC mapping when traffic is sent to a LISP-capable site?
Answer
Correct answer: D — The ingress tunnel router (ITR) is responsible for finding the EID-to-RLOC mapping for traffic destined to a LISP-capable site.
Community Votes
87% of anonymous learners picked answer D. Votes are pick records left by other test-takers — they are not the verified answer.
Community Insight
This question tests LISP component roles; the trap is confusing the device that queries the mapping system (ITR) with the infrastructure components that actually resolve the query (Map Resolver/Map Server).
In Cisco LISP architecture, the Ingress Tunnel Router (ITR) handles the encapsulation of traffic destined for LISP-capable sites. This page establishes that the ITR is the device responsible for finding the EID-to-RLOC mapping to successfully route this traffic.
Choosing 'map resolver' (A) because it processes the map-request, but the ITR is the device responsible for initiating the lookup to find the mapping for its outbound traffic.
Community Discussion (25 comments)
Din04
👍 1
Selected: D
Here's the answer from Claude: Answer: D. Ingress Tunnel Router (ITR) The ITR is the device that initiates the lookup for EID-to-RLOC mappings. Cisco’s LISP documentation describes it this way: when the ITR receives a packet destined for an EID, it first checks its map-cache. If there is no entry, it sends a Map-Request into the mapping system to learn the destination’s RLOC. Once it has the answer, it caches the mapping and encapsulates the packet toward that RLOC. Why the others are wrong A. Map Resolver. The MR receives the ITR’s Map-Request and helps resolve it, either by answering or by forwarding it toward the right ETR. It acts on the ITR’s behalf, but the ITR is the device responsible for finding the mapping. B. Egress Tunnel Router. The ETR registers its site’s EID-to-RLOC mappings with the map server and decapsulates incoming traffic. It publishes mappings and doesn’t look them up. C. Map Server. The MS stores the registrations from ETRs and doesn’t search for mappings on behalf of traffic. The ITR asks, the MR resolves, the MS stores, and the ETR registers. An exam question about who looks up the mapping is almost always about the ITR. In SD-Access, the fabric edge node plays this role when it sends a Map-Request to the control plane node.
studyguy42
👍 1
Selected: A
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
c48ef2b_111
👍 1
Selected: A
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.
simcos
👍 3
Selected: A
A was my answer. I afterwards asked copilot and deepseek and they both said A
zbeugene7
👍 3
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.
AbdullahMohammad251
👍 1
Selected: D
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.
Shri_Fcb10
👍 2
Selected: 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
nobodyknows11
👍 17
Selected: D
Passed My Exam on 15th , 100% From here, Three Labs GLBP, BGP R1 R3, Netflow IP Sla.
Shri_Fcb10
👍 1
Congratulations @nobodyknows11
CCAL
👍 2
I thought Labs GLBP, Netflow IP Sla were absolute,
Asombrosso
👍 2
Selected: D
An ITR is responsible for finding EID-to-RLOC mappings for all traffic destined for LISP-capable sites.
ihateciscoreally
👍 3
another broken question, one word changes question's whole meaning.
Lungful
👍 1
I assume you mean the answer is ITR due to "finding" and the line above is just a typo.
Networkfate
👍 6
Publish means ; ETR Finding means: ITR
Networkfate
👍 1
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
Networkfate
👍 1
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 Answer is ETR keyword"publish"
Symirnian
👍 3
Selected: D
Responsible means to search for RLOC and route the traffic in time. So D.
Quentin_
👍 11
Selected: D
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.
Clauster
👍 4
Selected: 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
Badger_27
👍 2
Selected: D
D - read the working of the question.
Opreis
👍 2
Selected: D
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
Nickplayany
👍 1
Selected: C
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
Nickplayany
👍 2
D is the correct my bad. I totally misunderstood this.
MikeyPher
👍 1
I think the answer is D. An ITR is responsible for finding EID-to-RLOC mappings for all traffic destined for LISP-capable sites
snarkymark
👍 1
Agree D, https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_lisp/configuration/15-sy/irl-15-sy-book/irl-overview.pdf
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Expert Analysis
Why the Answer Is Correct
The Ingress Tunnel Router (ITR) is the device responsible for finding EID-to-RLOC mappings for all traffic destined for LISP-capable sites. When an ITR receives an inbound packet destined for an EID, it checks its local map cache. If no mapping exists, the ITR is responsible for sending a Map-Request to the mapping system to find the correct RLOC, allowing it to encapsulate and forward the packet.Why the Other Options Are Wrong
The egress tunnel router (ETR) decapsulates LISP packets at the destination site, rather than finding mappings for outbound traffic. The map server (MS) accepts and registers EID-to-RLOC mappings from ETRs into the LISP mapping database, but it does not initiate the lookup for forwarding traffic. The map resolver (MR) receives Map-Requests from ITRs and queries the mapping database on their behalf; while it assists in the resolution, the ITR is the device fundamentally responsible for finding and caching the mapping for its traffic.Community Comment Notes
Several commenters correctly identified the ITR by citing the exact Cisco documentation phrasing, such as Quentin_ who noted "An ITR is responsible for finding EID-to-RLOC mappings". Others, like Clauster, provided the official Cisco LISP overview PDF to confirm the answer. Some users initially chose the map resolver, but as zbeugene7 pointed out, the question asks what device is "responsible for finding the mapping," which is the ITR since it triggers the lookup to route its traffic.Official Reference
Exam Strategy
Memorize the specific functional verbs tied to each LISP component in the Cisco documentation (e.g., ITR 'finds', ETR 'decapsulates', MS 'registers', MR 'resolves'). When a question asks which device is 'responsible' for an action related to forwarding traffic, it is almost always the ITR or ETR.
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