350-401 Question 111
Single answerAn enterprise network is deploying LISP to enable efficient communication between branches and datacenters. The network engineer configures LISP with Map-Resolvers (MR) and Map-Servers (MS). During verification, they observe that endpoint identifiers (EIDs) are successfully registered with the Map-Server, but remote sites fail to reach the EIDs over the WAN. What is the most likely cause of the issue?
- A
The Map-Resolver is not configured with the correct Locator/ID mappings.
- B
The ingress tunnel routers (ITRs) are not configured to encapsulate traffic to the registered EIDs.
- C
The endpoint identifiers (EIDs) are not correctly registered with the Map-Server.
- D
The egress tunnel router (ETR) is not advertising its RLOCs to the WAN.
Show answer and explanation
Correct answer: B
Explanation
In a LISP deployment, ingress tunnel routers (ITRs) are responsible for encapsulating traffic destined for EIDs into LISP packets. If the ITRs are not properly configured to encapsulate traffic, communication to the remote EIDs will fail, even if the EIDs are registered with the Map-Server and RLOCs are advertised by the ETRs. This highlights the critical role of ITRs in ensuring successful LISP functionality.
- A. Incorrect.
Incorrect. The Map-Resolver is responsible for resolving EIDs to RLOCs but does not maintain the Locator/ID mappings directly. This is not the cause of the issue described in the scenario.
- B. Correct.
Correct. If the ingress tunnel routers (ITRs) are not configured to encapsulate traffic to the registered EIDs, traffic will fail to reach the remote sites, even though the EIDs are properly registered with the Map-Server.
- C. Incorrect.
Incorrect. The scenario explicitly mentions that EIDs are successfully registered with the Map-Server, so this is not the issue.
- D. Incorrect.
Incorrect. While the egress tunnel router (ETR) is responsible for advertising its RLOCs, the issue described in the scenario points to ITR configuration, not ETR advertising.