The answer is that R1 has an 'mpls ldp advertise-labels' command filtering the label advertisement for 10.3.3.0/24. This is correct because while the LDP session is fully operational between R1 and R2, R1's forwarding table shows an "Untagged" outgoing label for the prefix, even though R2's table shows it is assigning label 17 and sending it out Serial0/0/0. The mismatch indicates that R2 is advertising the label, but R1 is either not requesting it or is filtering the incoming advertisement—and since the neighbor state is "Oper" and R2 clearly has the label, the root cause is a label advertisement filter applied on R1. On the Cisco CCNP ENARSI 300-410 exam, this scenario tests your ability to distinguish between LDP neighbor issues and label distribution policies; a common trap is assuming the problem is a missing route or a broken session. Remember the memory tip: "If the neighbor is up but the label is stuck, check the filter—don't just blame the luck."
300-410 Network Logging and Syslog Practice Question
This 300-410 practice question tests your understanding of network logging and syslog. 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.
MPLS network with LDP enabled. Routers R1 and R2 are directly connected. R1 has:
mpls ip
interface Serial0/0/0
mpls ip
R2 has:
mpls ip
interface Serial0/0/0
mpls ip
R1 shows:
R1# show mpls ldp neighbor
Peer LDP Ident: 10.2.2.2:0; Local LDP Ident: 10.1.1.1:0
TCP connection: 10.2.2.2.646 - 10.1.1.1.646
State: Oper; Msgs sent/rcvd: 10/10; Downstream
Up time: 00:00:30
LDP discovery sources:
Serial0/0/0, Src IP addr: 10.2.2.2
R1# show mpls forwarding-table
Local tag Outgoing tag Prefix Bytes tag switched Outgoing interface
16 Untagged 10.3.3.0/24 0 Serial0/0/0
R2 shows:
R2# show mpls forwarding-table
Local tag Outgoing tag Prefix Bytes tag switched Outgoing interface
16 17 10.3.3.0/24 0 Serial0/0/0
R1 is not installing a label for 10.3.3.0/24 from R2. What is the root cause?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
R1 has an 'mpls ldp advertise-labels' command that filters the label for 10.3.3.0/24.
LDP neighbors are established, but R1 is not receiving a label for 10.3.3.0/24 from R2. This could be due to a label filtering or the route not being in R2's routing table. The output shows R2 has an outgoing label 17 for that prefix, but R1 shows 'Untagged'. This indicates that R2 is not advertising a label to R1 for that prefix. Possible causes: R2 has a 'mpls ldp label' filter blocking the advertisement, or R1 is not requesting labels due to a 'mpls ldp advertise-labels' command. The correct answer is that R1 has a label advertisement filter.
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.
✓
R1 has an 'mpls ldp advertise-labels' command that filters the label for 10.3.3.0/24.
Why this is correct
This command can prevent R1 from advertising labels for certain prefixes, causing R1 to receive 'Untagged'.
The prefix 10.3.3.0/24 is not in R2's routing table.
Why it's wrong here
R2 has an outgoing label for it, so it must be in the routing table.
✗
There is an MTU mismatch on the serial link.
Why it's wrong here
MTU mismatch would affect LDP discovery, but neighbor is up.
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.
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 300-410 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 300-410 OSPF questions on adjacency and route selection.
Network Logging and Syslog — This question tests Network Logging and Syslog — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: R1 has an 'mpls ldp advertise-labels' command that filters the label for 10.3.3.0/24. — LDP neighbors are established, but R1 is not receiving a label for 10.3.3.0/24 from R2. This could be due to a label filtering or the route not being in R2's routing table. The output shows R2 has an outgoing label 17 for that prefix, but R1 shows 'Untagged'. This indicates that R2 is not advertising a label to R1 for that prefix. Possible causes: R2 has a 'mpls ldp label' filter blocking the advertisement, or R1 is not requesting labels due to a 'mpls ldp advertise-labels' command. The correct answer is that R1 has a label advertisement filter.
What should I do if I get this 300-410 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 300-410 OSPF questions on adjacency and route selection.
What is the key concept behind this question?
OSPF neighbours must agree on key parameters.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
This 300-410 practice question is part of Courseiva's free Cisco certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 300-410 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.