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350-401 · Question #568

How are map-register messages sent in a LISP deployment?

The correct answer is C. egress tunnel routers to map servers to determine the appropriate egress tunnel router. In a LISP deployment, Egress Tunnel Routers (ETRs) send map-register messages to map servers to publish the mappings between their Endpoint Identifiers (EIDs) and Routing Locators (RLOCs).

Submitted by tyler.j· Mar 6, 2026Architecture

Question

How are map-register messages sent in a LISP deployment?

Options

  • Aegress tunnel routers to map resolvers to determine the appropriate egress tunnel router
  • Bingress tunnel routers to map servers to determine the appropriate egress tunnel router
  • Cegress tunnel routers to map servers to determine the appropriate egress tunnel router
  • Dingress tunnel routers to map resolvers to determine the appropnate egress tunnel router

How the community answered

(28 responses)
  • A
    4% (1)
  • B
    4% (1)
  • C
    93% (26)

Why each option

In a LISP deployment, Egress Tunnel Routers (ETRs) send map-register messages to map servers to publish the mappings between their Endpoint Identifiers (EIDs) and Routing Locators (RLOCs).

Aegress tunnel routers to map resolvers to determine the appropriate egress tunnel router

Map resolvers are used by ITRs to query for EID-to-RLOC mappings, not to register mappings; ETRs send map-register messages to map servers.

Bingress tunnel routers to map servers to determine the appropriate egress tunnel router

Ingress Tunnel Routers (ITRs) primarily send map-request messages to Map Resolvers to learn EID-to-RLOC mappings, they do not send map-register messages for their own EIDs.

Cegress tunnel routers to map servers to determine the appropriate egress tunnel routerCorrect

Egress Tunnel Routers (ETRs) are responsible for informing the LISP mapping system about the EIDs they are authoritative for and their corresponding RLOCs. They send map-register messages to a Map Server (MS) to register these EID-to-RLOC mappings, allowing other LISP devices to query for reachability information.

Dingress tunnel routers to map resolvers to determine the appropnate egress tunnel router

ITRs send map-request messages to Map Resolvers, while map-register messages are sent by ETRs to Map Servers for registration, not resolution.

Concept tested: LISP Map Register message flow

Source: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_lisp/configuration/xe-16/irl-xe-16-book/irl-overview.html

Topics

#LISP#map-register#ETR#map server

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