- A
Disabling TTL propagation prevents traceroute from revealing the internal LSR hops.
Correct. With TTL propagation disabled, traceroute shows only the ingress and egress LSRs, hiding the core.
- B
The command 'no mpls ip propagate-ttl' is used to disable TTL propagation on a Cisco IOS router.
Correct. This is the exact command to disable TTL propagation globally or per interface.
- C
The command 'no mpls ip ttl-propagate' is used to disable TTL propagation.
Why wrong: Incorrect. The correct command is 'no mpls ip propagate-ttl'. The syntax 'ttl-propagate' is invalid.
- D
When TTL propagation is disabled, traceroute shows every LSR hop in the MPLS core.
Why wrong: Incorrect. Disabling TTL propagation hides the core hops; traceroute shows only ingress and egress.
- E
When TTL propagation is disabled, the TTL value is decremented normally at each LSR hop.
Why wrong: Incorrect. When disabled, the MPLS TTL is not decremented; it remains constant across the core.
Quick Answer
The correct answer is that the command 'no mpls ip propagate-ttl' disables TTL propagation, which hides core MPLS hops from traceroute. This works because, by default, the IP TTL is decremented at each label-switched router, revealing the entire path; when propagation is disabled, the ingress LSR copies the IP TTL into the MPLS label once, and the core routers do not decrement it, so traceroute only shows the ingress and egress LSRs. On the Cisco CCNP ENARSI 300-410 exam, this concept tests your understanding of MPLS security and network visibility, often appearing as a multiple-choice trap where you must distinguish the exact command syntax from distractors like 'no mpls ip ttl-propagate'. A common memory tip is to think of "propagate" as spreading the TTL across all hops—disabling it stops that spread, hiding the core topology.
300-410 MPLS Operations Practice Question
This 300-410 practice question tests your understanding of mpls operations. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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.
Related concept
Read the scenario before looking for a memorised answer.
- ✓
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.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
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.
- ✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Command / output trap
Incorrect. The correct command is 'no mpls ip propagate-ttl'. The syntax 'ttl-propagate' is invalid.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
- Use explanations to understand the rule behind the answer.
TExam Day Tips
- Underline the problem statement mentally.
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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FAQ
Questions learners often ask
What does this 300-410 question test?
MPLS Operations — This question tests MPLS Operations — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this 300-410 question wrong?
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 18, 2026
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