A new PE router is configured to run OSPF as an IGP with LDP on all interfaces. The engineer is trying to prevent black holes after convergence when the PERSON device loses an LDP session with other…

Question

Options

• AConfigure the mpls ldp session protection and mpls label protocol ldp commands on the
• BConfigure the mpls ldp discovery targeted-hello accept and mpls ldp session protection
• CConfigure the new PE router with the mpls ldp session protection command and on neighboring
• DConfigure the new PE router with the mpls ldp session protection command on interfaces with

• B
  7% (1)
• C
  73% (11)
• D
  20% (3)

Explanation

Option C is correct because LDP session protection requires a two-sided configuration: the local PE router must have mpls ldp session protection enabled, and the neighboring PE routers must also be configured to accept and maintain targeted LDP hello sessions. Targeted hellos keep a backup LDP session alive across the network even when the direct link session drops, preventing black holes during OSPF reconvergence.

Why the distractors are wrong:

• Option A pairs mpls ldp session protection with mpls label protocol ldp, which simply designates LDP as the label protocol - it plays no role in session protection or targeted hellos, making it an irrelevant addition.
• Option B includes mpls ldp discovery targeted-hello accept, which is correct for accepting targeted hellos, but the option omits the required configuration on neighboring routers, leaving the feature incomplete.
• Option D implies applying mpls ldp session protection on a per-interface basis, but the command is configured globally (not per-interface), and again ignores the need for neighbor-side configuration.

Memory tip: Think of it as a "buddy system" - LDP session protection only works when both sides are set up. The local router initiates targeted hellos; neighbors must be configured to sustain them. If only one side is configured, the backup session never fully forms.

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