An engineer is implementing MPLS to monitor within the MPLS domain. Which must the engineer perform to prevent packets from being forwarded beyond the service provider domain when the LSP is down?

Question

Options

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

• A
  5% (2)
• B
  3% (1)
• C
  10% (4)
• D
  82% (32)

Explanation

In MPLS OAM, LSP echo request packets (used for MPLS ping and traceroute) must use a destination IP address in the 127.x.y.z/8 range (the loopback address space). This is defined in RFC 4379. When the LSP is down and an echo request packet reaches an LSR that does not have a valid label forwarding entry, using a 127.x.y.z address as the destination ensures the packet is processed locally and not forwarded via IP routing beyond the MPLS domain. Since 127.0.0.0/8 addresses are non-routable and are loopback addresses on every IP device, any packet destined for this range that escapes the MPLS domain will be dropped by the receiving router rather than being forwarded further, effectively containing the packet within the SP domain.

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