mediumMultiple Choice
300-410 Practice Question: Runs the following command to troubleshoot an…
A network engineer runs the following command to troubleshoot an MPLS Operations issue:
R1# debug mpls ldp transport 10.1.1.1
Output:
*Mar 1 00:01:23.456: LDP: Sent hello to 10.1.1.1 (UDP 646) on GigabitEthernet0/0 *Mar 1 00:01:23.789: LDP: Received hello from 10.1.1.1 (UDP 646) on GigabitEthernet0/0 *Mar 1 00:01:24.012: LDP: Opened TCP connection to 10.1.1.1:646 *Mar 1 00:01:24.345: LDP: Initialization msg sent to 10.1.1.1 *Mar 1 00:01:24.678: LDP: Initialization msg received from 10.1.1.1 *Mar 1 00:01:25.001: LDP: Session with 10.1.1.1:0 (0x1234) is UP
What does this output indicate?
⚠ Common exam trap
300-410 often tests whether candidates can read the LDP state machine — many see 'Initialization msg' and assume the session is stuck, missing that the subsequent 'Session ... is UP' line confirms successful establishment.
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
✓
LDP session with neighbor 10.1.1.1 is successfully established
The debug output shows the full LDP session establishment sequence: hello exchange over UDP 646, TCP connection to port 646, initialization message exchange, and finally 'Session ... is UP.' This confirms that the LDP session with neighbor 10.1.1.1 has been successfully established.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
LDP session with neighbor 10.1.1.1 is successfully established
Why this is correct
The log shows the full LDP discovery and session sequence: hello exchange over UDP 646, TCP connection, Initialization message exchange, then session state UP. That final UP state confirms the label distribution adjacency with 10.1.1.1 formed successfully.
- ✗
LDP discovery via multicast hello failed
Why it's wrong here
Hello messages were both sent and received over UDP 646 on GigabitEthernet0/0, so discovery succeeded. Multicast hello is the default LDP discovery mechanism for finding link-local peers; it would be the failing component only if no hello were received, which is not the case here.
- ✗
TCP connection to 10.1.1.1 was refused
Why it's wrong here
The log shows the TCP connection opened and the session reaching UP state, so refusal never occurred. A refused connection would show a TCP error or session down message; this output confirms LDP adjacency formed successfully, making the option inconsistent with the observed Initialization exchange and UP notification.
- ✗
LDP session is stuck in initialization state
Why it's wrong here
The log shows the session reached UP after TCP establishment and bidirectional Initialization message exchange, so it is not stuck. The Initialization state is transient and is left once both peers send and accept Initialization messages; a stuck session would show repeated Initialization retransmissions without the UP confirmation.
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Related to this question
Learn chapter
Device Management and Network Monitoring (SNMP, Syslog, NetFlow)
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.
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.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Cisco exam blueprint
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