When configuring traffic engineering tunnels in Cisco MPLS core network, you see the traffic is not taking the expected path in the core. Which command do you use to quickly check path of a TE tunnel?

The show mpls traffic-engineering tunnels command is the primary and most direct method for verifying the state and path of an MPLS Traffic Engineering (TE) tunnel on a Cisco router. This command provides detailed output from the head-end router's perspective, including the tunnel's administrative and operational status, its signaling information, and, most importantly, the explicit path (Explicit Route Object - ERO) it is currently using. This allows an administrator to quickly compare the active path against the intended path to diagnose any discrepancies without sending active probes through the network.

A. Traceroute mpls ipv4 -tunnel destination: While a valid tool for tracing an LSP, the show command is a more immediate and comprehensive check of the tunnel's programmed state. The syntax shown is also imprecise.
B. Ping: This command is used to test end-to-end IP reachability and provides no information about the intermediate path taken by the packets.
D. traceroute: A standard IP traceroute operates at Layer 3 and will not show the Layer 2.5 label-switched path within the MPLS core; it typically obscures the core by showing the tunnel as a single hop.

1. Cisco IOS MPLS Command Reference: The documentation for the show mpls traffic-engineering tunnels command states its purpose is "To display information about Multiprotocol Label Switching (MPLS) traffic engineering tunnels." The sample output explicitly includes sections for "Path

" "Explicit Route

" and "Current LSP" path

confirming it is the correct tool for this task.

Source: Cisco

Cisco IOS MPLS Command Reference

"show mpls traffic-engineering tunnels" command description.

2. Cisco Press

MPLS Configuration on Cisco IOS Software: In the chapter on MPLS Traffic Engineering

the verification section highlights this command. It states

"The most useful command to verify the TE tunnel state is the show mpls traffic-engineering tunnels [tunnel number] command... This command shows the tunnel state

the path the tunnel takes

and the signaling information."

Source: Aviva Garrett

et al.

MPLS Configuration on Cisco IOS Software

Cisco Press

2005

Chapter 6

"Verifying the TE Tunnel State" section.

3. Cisco Configuration Guide: In the guide for MPLS Traffic Engineering

the verification steps consistently rely on this command. The guide explains

"To verify that the tunnel is up and carrying traffic

and to see the explicit path that the tunnel is using

use the show mpls traffic-engineering tunnels command."

Source: Cisco

MPLS Traffic Engineering Path Calculation and Setup Configuration Guide

Cisco IOS Release 15M&T

"Verifying MPLS TE Tunnel Configuration" section.