Question 1,398 of 2,015

MPLS →hardMultiple ChoiceObjective-mapped

Quick Answer

The answer is that the LDP session with neighbor 10.5.5.4 is not established because the output shows "no hello (expired)" under the GigabitEthernet0/0 interface. This status indicates that Router R5 is transmitting (xmit) LDP hello messages out of that interface but has not received any hello messages back from 10.5.5.4 within the hello hold timer, causing the neighbor relationship to expire. In MPLS LDP operation, hello messages are sent periodically to discover and maintain link-level neighbors; when they expire, the LDP session cannot form or is torn down. On the ENCOR 350-401 exam, this scenario tests your ability to interpret the "show mpls ldp discovery" command and distinguish between a neighbor that is discovered (receiving hellos) versus one that is merely transmitting hellos without a response. A common trap is assuming that "xmit/recv" means a full session is up, but the "no hello (expired)" flag clarifies that only one-way communication exists. Memory tip: if you see "no hello," think "no hello, no session"—the neighbor is sending but not receiving.

CCNP MPLS Practice Question

This 350-401 practice question tests your understanding of mpls. 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 runs the following command on Router R5:

R5# show mpls ldp discovery

Local LDP Identifier: 10.5.5.5:0 Discovery Sources:

Interfaces:

GigabitEthernet0/0: xmit/recv LDP Id: 10.5.5.4:0, no hello (expired) GigabitEthernet0/1: xmit/recv LDP Id: 10.5.5.6:0

Based on this output, what is the state of the LDP session with neighbor 10.5.5.4?

Question 1hardmultiple choice

Read the full MPLS explanation →

A
The LDP session with 10.5.5.4 is operational because the interface is in xmit/recv mode.
Why wrong: The 'xmit/recv' indicates the interface is sending and receiving hellos, but the neighbor state shows 'no hello (expired)', meaning no hello received from that neighbor.
B
The LDP session with 10.5.5.4 is not established because no hello messages have been received from that neighbor.
The 'no hello (expired)' indicates that the hello timer expired without receiving a hello, so the session cannot be established.
C
The LDP session with 10.5.5.4 is down because the interface is not operational.
Why wrong: The interface is in xmit/recv mode, meaning it is operational for sending/receiving hellos, but the neighbor is not responding.
D
The LDP session with 10.5.5.4 is using targeted discovery.
Why wrong: The discovery is interface-based (GigabitEthernet0/0), not targeted.

Full breakdown with real-world context →

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 10.5.5.4 is not established because no hello messages have been received from that neighbor.

The output shows LDP discovery sources. For Gi0/0, the neighbor 10.5.5.4:0 has 'no hello (expired)', meaning the hello messages have not been received recently, so the neighbor is considered down or the session is not established.

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 with 10.5.5.4 is operational because the interface is in xmit/recv mode.
Why it's wrong here
The 'xmit/recv' indicates the interface is sending and receiving hellos, but the neighbor state shows 'no hello (expired)', meaning no hello received from that neighbor.
✓
The LDP session with 10.5.5.4 is not established because no hello messages have been received from that neighbor.
Why this is correct
The 'no hello (expired)' indicates that the hello timer expired without receiving a hello, so the session cannot be established.
Related concept
OSPF neighbours must agree on key parameters.
✗
The LDP session with 10.5.5.4 is down because the interface is not operational.
Why it's wrong here
The interface is in xmit/recv mode, meaning it is operational for sending/receiving hellos, but the neighbor is not responding.
✗
The LDP session with 10.5.5.4 is using targeted discovery.
Why it's wrong here
The discovery is interface-based (GigabitEthernet0/0), not targeted.

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
The 'xmit/recv' indicates the interface is sending and receiving hellos, but the neighbor state shows 'no hello (expired)', meaning no hello received from that neighbor.

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.

What to study next

Got this wrong? Here's your next step.

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.

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FAQ

Questions learners often ask

What does this 350-401 question test?

MPLS — This question tests MPLS — OSPF neighbours must agree on key parameters..

What is the correct answer to this question?

The correct answer is: The LDP session with 10.5.5.4 is not established because no hello messages have been received from that neighbor. — The output shows LDP discovery sources. For Gi0/0, the neighbor 10.5.5.4:0 has 'no hello (expired)', meaning the hello messages have not been received recently, so the neighbor is considered down or the session is not established.

What should I do if I get this 350-401 question wrong?

What is the key concept behind this question?

OSPF neighbours must agree on key parameters.

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