350-501 MPLS and Segment Routing Practice Question
Which LDP mode uses downstream unsolicited label distribution and liberal label retention?
⚠ Common exam trap
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.
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
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.
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.
- ✗
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.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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