Which utility can you use to locate MPLS faults?

MPLS traceroute (traceroute mpls) is the specific utility designed to locate and isolate data plane faults within a Label Switched Path (LSP). It operates by sending a series of MPLS echo requests (the same mechanism used by LSP Ping) with incrementally increasing Time-to-Live (TTL) values. This process allows an administrator to trace the LSP hop-by-hop from the ingress router to the egress router, thereby pinpointing the exact node where forwarding fails. While MPLS LSP ping can detect a connectivity failure, MPLS traceroute is the precise tool used to locate that failure.

C. MPLS LSP ping: This utility (ping mpls) primarily verifies end-to-end connectivity for a specific Forwarding Equivalence Class (FEC). It confirms that a fault exists but does not, by itself, locate the specific hop where the fault occurred.
B. EEM: The Embedded Event Manager (EEM) is a powerful scripting and automation framework within Cisco IOS. It is not a dedicated utility for diagnosing or locating MPLS faults.
D. QoS: Quality of Service (QoS) is a suite of technologies used to manage network traffic, prioritize packets, and ensure performance. It is unrelated to fault location and diagnostics.

1. Cisco IOS XE MPLS Configuration Guide: In the "MPLS LSP Ping and Traceroute" section

the documentation makes a clear distinction: "The MPLS LSP Ping feature is used to check the connectivity of label switched paths (LSPs)... The MPLS LSP Traceroute feature is used to isolate a fault in the LSP." This directly supports that traceroute is the utility for locating faults.

Source: Cisco

"MPLS Configuration Guide

Cisco IOS XE Gibraltar 16.12.x"

Chapter: MPLS Operations

Administration

and Maintenance.

2. RFC 8029

"Detecting Multiprotocol Label Switched (MPLS) Data-Plane Failures": This document defines the core protocol for MPLS OAM

often called "LSP Ping." It describes the MPLS echo request/reply mechanism. Section 3

"The MPLS Echo Request and Echo Reply Messages

" details how manipulating the TTL field in the echo request enables a traceroute function to discover the path and locate failures. This establishes traceroute as a specific application of the protocol for fault location.

Source: RFC 8029

Section 3

Paragraph 1.

3. MPLS Fundamentals by Luc De Ghein (Cisco Press): This authoritative book states

"LSP traceroute is an extension of LSP ping and is used to trace the path of an LSP hop by hop... This is a very useful tool to localize a problem in the MPLS data plane."

Source: De Ghein

L. (2006). MPLS Fundamentals. Cisco Press. Chapter 10

"MPLS OAM".