AN engineer is implementing MPLS OAM to monitor traffic within the MPLS domain. Which action must the engineer perform to prevent from being forwarded beyond the service provider domain when the LSP i

Question

Options

• ADisable IP redirects only on outbound interfaces
• BImplement the destination address for the LSP echo request packet in the 127.x.y.z/8 network
• CDisable IP redirects on all ingress interfaces
• DConfigure a private IP address as the destination address of the headend router of Cisco MPLS TE.

• A
  11% (3)
• B
  82% (23)
• C
  4% (1)
• D
  4% (1)

Explanation

MPLS OAM LSP Echo Request Containment

Using the 127.x.y.z/8 loopback address range as the destination for LSP echo request packets is the correct approach because routers are configured to never forward packets destined for the 127.0.0.0/8 (loopback) address range beyond a single device - if the LSP fails and the packet reaches a router without a valid label path, the packet is dropped locally rather than being forwarded into the broader internet or beyond the SP domain. This is a deliberate design feature of MPLS OAM (RFC 4379), ensuring that ping/traceroute test packets stay contained within the MPLS domain.

Why the distractors are wrong:

• A is incorrect because disabling IP redirects only on outbound interfaces does not prevent packet leakage when an LSP is down; IP redirects are a separate routing mechanism.
• C is incorrect for the same reason - disabling IP redirects on ingress interfaces addresses redirect behavior, not LSP failure containment.
• D is incorrect because using a private IP address as the TE headend destination does not guarantee the packet won't be forwarded beyond the SP domain, as private addresses can still be routed internally.

Memory Tip: Think "127 = Stay Local" - the 127.x.y.z range is the loopback range that no router will forward, making it the perfect "safety net" to trap MPLS OAM packets if the LSP goes down.

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