- A
EIGRP is not supported with MPLS; OSPF or IS-IS must be used.
Why wrong: EIGRP can be used with MPLS; any IGP that provides reachability works.
- B
The 'mpls ldp router-id' command references Loopback0, but no loopback interface is configured, causing LDP to fail.
If the specified router-id interface does not exist, LDP cannot determine its router ID and will not operate. A loopback must be created.
- C
The 'mpls ip' command is missing on GigabitEthernet0/1, so MPLS will not work on that interface.
Why wrong: While MPLS is only enabled on one interface, that is not necessarily a problem if only one neighbor is needed. The question asks for the problem; the missing loopback is more critical.
- D
CEF must be enabled under each interface, not just globally.
Why wrong: Global CEF enables CEF on all interfaces; no per-interface command is needed.
300-410 MPLS Operations Practice Question
This 300-410 practice question tests your understanding of mpls operations. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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.
Examine this MPLS configuration on a router:
ip cef
!
interface GigabitEthernet0/0 ip address 172.16.1.1 255.255.255.252
mpls ip !
interface GigabitEthernet0/1 ip address 172.16.2.1 255.255.255.252
!
router eigrp 100 network 172.16.0.0
! mpls ldp router-id Loopback0 force
What is the problem with this configuration?
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 'mpls ldp router-id' command references Loopback0, but no loopback interface is configured, causing LDP to fail.
The LDP router-id is set to Loopback0, but Loopback0 is not configured. This will cause LDP to fail to establish a router ID, and LDP sessions will not form. Additionally, EIGRP is used but that is fine. The missing loopback interface is the key issue.
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.
- ✗
EIGRP is not supported with MPLS; OSPF or IS-IS must be used.
Why it's wrong here
EIGRP can be used with MPLS; any IGP that provides reachability works.
- ✓
The 'mpls ldp router-id' command references Loopback0, but no loopback interface is configured, causing LDP to fail.
- ✗
The 'mpls ip' command is missing on GigabitEthernet0/1, so MPLS will not work on that interface.
Why it's wrong here
While MPLS is only enabled on one interface, that is not necessarily a problem if only one neighbor is needed. The question asks for the problem; the missing loopback is more critical.
- ✗
CEF must be enabled under each interface, not just globally.
Why it's wrong here
Global CEF enables CEF on all interfaces; no per-interface command is needed.
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
Global CEF enables CEF on all interfaces; no per-interface command is needed.
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 300-410 OSPF questions on adjacency and route selection.
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FAQ
Questions learners often ask
What does this 300-410 question test?
MPLS Operations — This question tests MPLS Operations — OSPF neighbours must agree on key parameters..
What is the correct answer to this question?
The correct answer is: The 'mpls ldp router-id' command references Loopback0, but no loopback interface is configured, causing LDP to fail. — The LDP router-id is set to Loopback0, but Loopback0 is not configured. This will cause LDP to fail to establish a router ID, and LDP sessions will not form. Additionally, EIGRP is used but that is fine. The missing loopback interface is the key issue.
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.
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Last reviewed: Jun 18, 2026
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.
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