350-501 Question #616: Real Exam Question with Answer & Explanation

Question

Refer to the exhibit. OSPF is running in the core, with MPLS configured on all links. A Cisco MPLS TE tunnel is configured with R1 as the headend and R4 as the tail-end router. As traffic on the network increases, the network engineering team is concerned about identifying failures between the tunnel endpoints. Which action should the engineering team take that will allow them to identify and locate any faults in the path?

Options

• AImplement NetFlow to determine whether traffic is traversing the egress interfaces as expected.
• BImplement an ICMP ping utility to send periodic test packets and identify the failure location.
• CImplement RSVP to determine whether bandwidth is properly allocated along the path.
• DImplement MPLS OAM with traceroute to follow the path and determine where packets are failing.

Explanation

To identify and locate faults within an MPLS Traffic Engineering (TE) tunnel path, the engineering team should utilize MPLS OAM (Operations, Administration, and Maintenance) with traceroute capabilities.

Common mistakes.

• A. NetFlow is a technology for collecting and analyzing IP traffic flow information, used for monitoring and accounting, but it does not actively identify or locate specific faults or pinpoint failures within an MPLS TE tunnel path.
• B. While ICMP ping can test end-to-end reachability, it operates at Layer 3 and does not follow the specific label-switched path of an MPLS TE tunnel. Therefore, it cannot accurately pinpoint faults within the MPLS domain itself.
• C. RSVP (Resource Reservation Protocol) is the signaling protocol used to establish and maintain MPLS TE tunnels and reserve bandwidth. It's part of the tunnel's setup and operation, but it is not a tool for actively identifying existing faults or pinpointing their location post-deployment.

Concept tested. MPLS TE OAM for fault localization

Reference. https://www.cisco.com/c/en/us/td/docs/ios_xr_sw/iosxr_6_2_2/mpls/configuration/guide/b-mpls-te-cg-iosxr-62x-book/b-mpls-te-cg-iosxr-62x-book_chapter_0110.html

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