- A
Downstream on demand with liberal retention
Why wrong: Liberal retention is typically paired with unsolicited distribution.
- B
Downstream unsolicited with liberal retention
This is the default LDP mode.
- C
Upstream unsolicited with liberal retention
Why wrong: Upstream distribution is not used in LDP.
- D
Downstream on demand with conservative retention
Why wrong: This is an alternative mode not default.
Question 259 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.
Which LDP mode uses downstream unsolicited label distribution and liberal label retention?
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
✓
Downstream unsolicited with liberal retention
Option B is correct because downstream unsolicited (DU) label distribution is the default mode in LDP, where each LSR advertises labels for all its directly connected prefixes to its neighbors without waiting for a request. Liberal label retention means the LSR stores all received label bindings, even if they are not currently used for forwarding, which enables rapid convergence upon topology changes.
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.
- ✗
Downstream on demand with liberal retention
Why it's wrong here
Liberal retention is typically paired with unsolicited distribution.
- ✓
Downstream unsolicited with liberal retention
Why this is correct
This is the default LDP mode.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Upstream unsolicited with liberal retention
Why it's wrong here
Upstream distribution is not used in LDP.
- ✗
Downstream on demand with conservative retention
Why it's wrong here
This is an alternative mode not default.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between label distribution modes (DU vs. DoD) and label retention modes (liberal vs. conservative), and candidates may confuse 'downstream unsolicited' with 'upstream unsolicited' or incorrectly associate liberal retention with DoD mode.
Detailed technical explanation
How to think about this question
In LDP, the combination of DU and liberal retention is the default behavior per RFC 5036, where each LSR advertises a label for every prefix in its routing table to all LDP peers. Liberal retention consumes more memory because all received labels are stored, but it allows immediate use of an alternate label when a primary next-hop fails, without needing to request a new label, thus reducing convergence time in MPLS networks.
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.
TExam Day Tips
- 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 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
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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 — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Downstream unsolicited with liberal retention — Option B is correct because downstream unsolicited (DU) label distribution is the default mode in LDP, where each LSR advertises labels for all its directly connected prefixes to its neighbors without waiting for a request. Liberal label retention means the LSR stores all received label bindings, even if they are not currently used for forwarding, which enables rapid convergence upon topology changes.
What should I do if I get this 350-501 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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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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