The answer is that the LDP session is operational with a holdtime of 15000 ms. This is correct because the output of the show mpls ldp neighbor command displays the state as "Oper," which directly indicates the Label Distribution Protocol session is fully established and functioning. The holdtime of 15000 ms, shown under the LDP discovery sources for the GigabitEthernet0/0 interface, defines how long the router will wait for a hello message before declaring the neighbor down, and the TCP connection on port 646 confirms the reliable transport layer for label exchange. On the ENCOR 350-401 exam, this command tests your ability to interpret LDP neighbor relationships and distinguish between the session state and discovery parameters; a common trap is confusing the holdtime with the hello interval or assuming the session is down if you see only one address bound. Remember the mnemonic "Oper is Open" to instantly recall that the state must be "Oper" for a working LDP session.
350-401 WAN Technologies Practice Question
This 350-401 practice question tests your understanding of wan technologies. Examine the command output carefully: the correct answer depends on what the output actually shows, not on general recall alone. 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.
A network engineer executes the following command on Router R2:
R2# show mpls ldp neighbor
Peer LDP Ident: 192.168.1.1:0; Local LDP Ident 192.168.1.2:0
TCP connection: 192.168.1.1.646 - 192.168.1.2.54321
State: Oper; Msgs sent/rcvd: 1234/1234; Downstream
Up time: 2d04h
LDP discovery sources:
GigabitEthernet0/0, Src IP addr: 192.168.1.1
holdtime: 15000 ms, hello interval: 5000 ms
Addresses bound to peer LDP Ident:
192.168.1.1 10.0.0.1
Based on this output, what is true about the LDP session?
The LDP session is down because the state is 'Oper'.
Why wrong: 'Oper' means operational, not down.
B
The LDP session is using UDP port 646 for the TCP connection.
Why wrong: LDP uses TCP port 646; the output shows TCP connection, not UDP.
C
The LDP session is operational and the holdtime is 15000 ms.
The state is 'Oper' and holdtime is explicitly shown as 15000 ms.
D
The LDP session is using the default hello interval of 5000 ms.
Why wrong: The hello interval is 5000 ms but it is not necessarily default; however, the question asks what is true, and the holdtime is explicitly correct.
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 is operational and the holdtime is 15000 ms.
The output shows an LDP neighbor with state 'Oper' (operational) and a TCP connection using well-known port 646. The holdtime and hello interval are displayed.
Key principle: OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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 is down because the state is 'Oper'.
Why it's wrong here
'Oper' means operational, not down.
✗
The LDP session is using UDP port 646 for the TCP connection.
Why it's wrong here
LDP uses TCP port 646; the output shows TCP connection, not UDP.
✓
The LDP session is operational and the holdtime is 15000 ms.
Why this is correct
The state is 'Oper' and holdtime is explicitly shown as 15000 ms.
The LDP session is using the default hello interval of 5000 ms.
Why it's wrong here
The hello interval is 5000 ms but it is not necessarily default; however, the question asks what is true, and the holdtime is explicitly correct.
Common exam traps
Common exam trap: OSPF can fail even when IP connectivity looks correct
OSPF neighbour formation depends on matching areas, timers, network type, authentication and passive-interface behaviour. Do not choose an answer only because the devices can ping.
Trap categories for this question
Command / output trap
LDP uses TCP port 646; the output shows TCP connection, not UDP.
Detailed technical explanation
How to think about this question
OSPF questions usually test the details that control adjacency and route selection. Read the neighbour state, area, router ID and interface configuration before deciding what is wrong.
KKey Concepts to Remember
OSPF neighbours must agree on key parameters.
Router ID selection can affect neighbour relationships and LSDB output.
OSPF cost influences the preferred path.
A route can appear in OSPF information but not become the installed route.
TExam Day Tips
→Check area mismatch first when OSPF adjacency fails.
→Review passive interfaces when a network is advertised but no neighbour forms.
→Use show ip ospf neighbor and show ip route clues carefully.
Key takeaway
OSPF neighbour adjacency depends on matching area, hello/dead timers, network type, and authentication — IP reachability alone is not enough.
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.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this 350-401 question in full detail.
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 350-401 OSPF questions on adjacency and route selection.
WAN Technologies — This question tests WAN Technologies — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The LDP session is operational and the holdtime is 15000 ms. — The output shows an LDP neighbor with state 'Oper' (operational) and a TCP connection using well-known port 646. The holdtime and hello interval are displayed.
What should I do if I get this 350-401 question wrong?
Review OSPF neighbour requirements — matching area type, hello and dead timers, network type, stub flags, and authentication. Study show ip ospf neighbor states (INIT, 2-WAY, FULL). Then practise related 350-401 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
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