hardMultiple Choice
300-410 Practice Question: Runs the following command to debug MPLS LDP…
A network engineer runs the following command to debug MPLS LDP session establishment:
R1# debug mpls ldp session
Output:
*Mar 1 00:01:23.456: LDP: Session with 10.0.0.2:0 (0x1234) is UP *Mar 1 00:01:24.567: LDP: Session with 10.0.0.2:0 (0x1234) is DOWN *Mar 1 00:01:25.678: LDP: Session with 10.0.0.2:0 (0x1234) is UP *Mar 1 00:01:26.789: LDP: Session with 10.0.0.2:0 (0x1234) is DOWN
What does this output indicate?
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
✓
The LDP session with 10.0.0.2 is flapping
The debug output shows the LDP session with neighbor 10.0.0.2 is flapping (repeatedly going UP and DOWN). This indicates instability in the LDP session.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
The LDP session with 10.0.0.2 is flapping
Why this is correct
Repeated UP/DOWN transitions for the same peer (10.0.0.2:0) within seconds indicate the LDP session is flapping, not merely failing once. The stem's constraint is session establishment instability, and the debug output directly evidences the session cycling between operational states, so this option matches the observed behaviour precisely.
- ✗
The LDP session with 10.0.0.2 is stable
Why it's wrong here
The log shows the session repeatedly transitioning UP then DOWN within seconds, which is flapping, not stability. A stable session would log UP once and remain without subsequent DOWN entries. Stability is what you would expect after the LDP session has fully converged and keepalives are exchanged normally.
- ✗
The LDP session with 10.0.0.2 is using targeted hello
Why it's wrong here
Targeted hello extends LDP discovery to non-directly-connected peers, but the log shows session state transitions, not discovery mechanism details. Session flapping here stems from keepalive or transport failure. Targeted hello would be relevant when establishing LDP sessions across a network where the peer is not on a directly connected subnet.
- ✗
The LDP session with 10.0.0.2 is down permanently
Why it's wrong here
The repeated UP/DOWN transitions show the session is flapping, not permanently down. A permanent failure would log a single DOWN or remain DOWN with no subsequent UP entries. Permanent down is the expected state when the LDP peer is unreachable or the session is administratively shut.
Go deeper
Related to this question
Learn chapter
OSPF Neighbor Adjacency and Basics
Key term
LDP Protocol
LDP, or Label Distribution Protocol, is a protocol that routers use to automatically exchange labels that enable MPLS (Multiprotocol Label Switching) to create fast, efficient paths for data packets across a network.
Key term
MPLS Label Distribution
MPLS Label Distribution is the process by which routers exchange labels that tell them how to forward packets across a network without looking at the IP address each time.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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