Exam 350-401 topic 1 question 63 discussion

https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_lisp/configuration/xe-3s/irl-xe-3s-book/irl-overview.html A. ETR 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.

n Egress Tunnel Router (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.

Answer is A. The ETR is the only device that publishes EID-to-RLOC mappings for a site. It publishes mappings to the Map Server. The MS Map-Server (MS) does not publish EID-to-RLOC mappings. Instead, it plays a passive, registrar-like role in the LISP architecture.

Map-Server: A network infrastructure component that learns of EID-Prefix mapping entries from an ETR, via the registration mechanism described below, or some other authoritative source if one exists. A Map-Server publishes these EID-Prefixes in a mapping database. https://datatracker.ietf.org/doc/html/rfc6833

this question is why cisco exams such. The ETR publishes EID to RLOC mappings for a site in one reference, another reference says the MS responds to map requests... thansk cisco.

A is correct The Egress Tunnel Router (ETR) is responsible for advertising and publishing the mappings between Endpoint Identifiers (EIDs) and Routing Locators (RLOCs) to other LISP devices within the network. D is wrong, MS (Map Server) is responsible for storing and managing the mappings between EIDs and RLOCs. It doesn't publish these mappings directly to the site, instead it serves as a repository for mapping information.

D. MS (Map Server) In the Locator/ID Separation Protocol (LISP), the Map Server (MS) is responsible for publishing EID-to-RLOC (Endpoint Identifier to Routing Locator) mappings for a site. The Map Server stores and manages the mapping information, which associates EID prefixes with the corresponding RLOCs. When an Ingress Tunnel Router (ITR) needs to encapsulate a packet destined to an EID, it queries the Map Server to obtain the RLOCs associated with that EID. The Map Server then provides the necessary mapping information to the ITR, allowing it to encapsulate the packet with the appropriate RLOCs. Option A, ETR (Egress Tunnel Router), is responsible for decapsulating packets arriving at a site and forwarding them to the correct EID based on the mapping information obtained from the Map Resolver (MR).

Answer: A LISP Egress Tunnel Router 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. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_lisp/configuration/15-mt/irl-15-mt-book/irl-overview.pdf

In my opinion, correct answer is A: ETR. The reasoning is based on Cisco OCG: "When setting up LISP, the ETR routers need to be configured with the EID prefixes within the LISP site that will be registered with the MS". If by "publish" we understand "make public", this is the job of the ETR. The ETR is responsible to inform the MS/MR "Hey, this is who I am (RLOC), these are the subnets attached to me (EIDs)".

A is correct After the ITR receives the EID-to-RLOC mapping from the ETR (or MS, if the ETR requested a proxy map reply), it is ready to send data from host1 to host2.

ask google

The LISP device that is responsible for publishing EID-to-RLOC mappings for a site is the Mapping Server (MS). The MS stores and manages the mapping database for a site or domain, and provides the mappings to the MR when requested. It is responsible for publishing EID-to-RLOC mappings to the Map-Resolvers (MRs) in the domain. When a router needs to find the RLOC for a given EID, it sends a Map-Request message to the MR. The MR then queries the MS for the mapping. The other LISP devices are responsible for different tasks: Ingress Tunnel Router (ITR): The ITR is responsible for encapsulating packets destined for LISP-capable sites in LISP headers and sending them to the MR. Egress Tunnel Router (ETR): The ETR is responsible for decapsulating LISP packets from the ITR and forwarding them to their final destination. Map-Resolver (MR): The MR is responsible for responding to Map-Request messages from ITRs and providing them with the RLOCs for the EIDs that they are requesting.

MS Service populates the HTDB MR Service resolves HTDB queries

Map server (MS): This is a network device (typically a router) that learns EID-to-prefix mapping entries from an ETR and stores them in a local EID-to-RLOC mapping database.

A is correct answer. Egress Tunnel Router (ETR) is the device (or function) that 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. During operation, an ETR sends periodic Map-Register messages to all its configured map servers. https://www.digitaltut.com/lisp-tutorial

I'm going to be the outlier here. The Map Server is what actually populates the Host Tracking Database inside the Control Plane. The word used here is "publishes". When devices connect, they register with the Map Server. That is how the HTDB gets populated. The HTDB is "the central repository of EID-to-fabric-edge" node bindings (EID-RLOC)

correct