350-501 Architecture Practice Question
An engineer is configuring LDP in an MPLS network. Which THREE are valid label distribution modes for LDP?
⚠ Common exam trap
Cisco often tests the misconception that Ordered Label Distribution Control can be paired with Downstream Unsolicited mode, but Ordered control is only valid with Downstream on Demand in LDP specifications.
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 on Demand with Independent Label Distribution Control
Downstream on Demand (DoD) with Independent Label Distribution Control allows a router to request a label mapping only when needed and to advertise bindings independently, as defined in RFC 5036. Option B is correct because Downstream Unsolicited (DU) with Conservative Label Retention means a router learns all label mappings but only stores those for routes it actively uses, which is a supported mode in MPLS LDP implementations. Option C is correct because Downstream Unsolicited with Liberal Label Retention is the default and most common mode, where a router stores all label mappings received from neighbors. Options D and E are incorrect because Ordered Label Distribution Control is typically used with DoD, not DU, and Liberal Label Retention is rarely paired with DoD due to resource waste.
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 Independent Label Distribution Control
Why this is correct
This is a valid combination.
- ✓
Downstream Unsolicited with Conservative Label Retention
Why this is correct
This is valid, though less common.
- ✓
Downstream Unsolicited with Liberal Label Retention
Why this is correct
This is the default mode for LDP.
- ✗
Downstream Unsolicited with Ordered Label Distribution Control
Why it's wrong here
Ordered control is associated with DoD, not DU.
- ✗
Downstream on Demand with Liberal Label Retention
Why it's wrong here
DoD mode uses conservative label retention inherently.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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