- A
Labels are advertised to all LDP peers for all known prefixes without a request.
Correct for downstream unsolicited mode.
- B
Labels are retained only for directly connected neighbors.
Why wrong: Liberal retention keeps all labels.
- C
Label advertisements are sent only for prefixes learned via BGP.
Why wrong: LDP advertises for IGP routes typically.
- D
Labels are advertised only when explicitly requested by a neighbor.
Why wrong: That is downstream on demand mode.
Question 627 of 1,000
350-501 MPLS and Segment Routing Practice Question
This 350-501 practice question tests your understanding of mpls and segment routing. 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.
An engineer is configuring MPLS LDP on a Cisco router. The router is using downstream unsolicited mode and liberal label retention. Which statement correctly describes the label advertisement behavior?
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
✓
Labels are advertised to all LDP peers for all known prefixes without a request.
In downstream unsolicited mode, the router advertises labels for all known prefixes to all neighbors, even if the neighbor did not request them. Liberal label retention keeps all received labels, even if not currently used.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Labels are advertised to all LDP peers for all known prefixes without a request.
Why this is correct
Correct for downstream unsolicited mode.
Related concept
OSPF neighbours must agree on key parameters.
- ✗
Labels are retained only for directly connected neighbors.
Why it's wrong here
Liberal retention keeps all labels.
- ✗
Label advertisements are sent only for prefixes learned via BGP.
Why it's wrong here
LDP advertises for IGP routes typically.
- ✗
Labels are advertised only when explicitly requested by a neighbor.
Why it's wrong here
That is downstream on demand mode.
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
- OSPF neighbours must agree on key parameters.
- Router ID selection can affect neighbour relationships and LSDB output.
- OSPF cost influences the preferred path.
- A route can appear in OSPF information but not become the installed route.
TExam Day Tips
- Check area mismatch first when OSPF adjacency fails.
- Review passive interfaces when a network is advertised but no neighbour forms.
- Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
Real-world example
How this comes up in practice
A network engineer at a university connects two campus buildings via a fibre link. Both routers run OSPF, but no adjacency forms — even though both routers can ping each other. The engineer finds one router is in area 0 and the other in area 1. OSPF adjacency requires matching area numbers, hello/dead timers, and network type. IP reachability alone is not enough.
What to study next
Got this wrong? Here's your next step.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 350-501 OSPF questions on adjacency and route selection.
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FAQ
Questions learners often ask
What does this 350-501 question test?
MPLS and Segment Routing — This question tests MPLS and Segment Routing — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: Labels are advertised to all LDP peers for all known prefixes without a request. — In downstream unsolicited mode, the router advertises labels for all known prefixes to all neighbors, even if the neighbor did not request them. Liberal label retention keeps all received labels, even if not currently used.
What should I do if I get this 350-501 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 350-501 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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Last reviewed: Jul 4, 2026
This 350-501 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 350-501 exam.
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