hardMultiple SelectObjective-mapped
300-410 Practice Question: Which TWO statements correctly describe the…
Which TWO statements correctly describe the behavior of TTL propagation in MPLS networks? (Choose TWO.)
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Disabling TTL propagation prevents traceroute from revealing the internal LSR hops.
In MPLS, TTL propagation can be disabled for security or to hide the core topology. When disabled, the IP TTL is copied to the MPLS label only at the ingress LSR, and at the egress LSR the MPLS TTL is copied back to the IP header. By default, TTL propagation is enabled. The command 'no mpls ip propagate-ttl' disables it. Option A is correct because disabling TTL propagation hides the core hops from traceroute. Option B is correct because the command to disable is indeed 'no mpls ip propagate-ttl'. Option C is false: the command is not 'no mpls ip ttl-propagate'. Option D is false: traceroute shows only the ingress and egress LSRs, not all hops. Option E is false: when disabled, the TTL is not decremented across the MPLS core.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Disabling TTL propagation prevents traceroute from revealing the internal LSR hops.
Why this is correct
Correct. With TTL propagation disabled, traceroute shows only the ingress and egress LSRs, hiding the core.
- ✓
The command 'no mpls ip propagate-ttl' is used to disable TTL propagation on a Cisco IOS router.
Why this is correct
Correct. This is the exact command to disable TTL propagation globally or per interface.
- ✗
The command 'no mpls ip ttl-propagate' is used to disable TTL propagation.
Why it's wrong here
Incorrect. The correct command is 'no mpls ip propagate-ttl'. The syntax 'ttl-propagate' is invalid.
- ✗
When TTL propagation is disabled, traceroute shows every LSR hop in the MPLS core.
Why it's wrong here
Incorrect. Disabling TTL propagation hides the core hops; traceroute shows only ingress and egress.
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When TTL propagation is disabled, the TTL value is decremented normally at each LSR hop.
Why it's wrong here
Incorrect. When disabled, the MPLS TTL is not decremented; it remains constant across the core.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.