- A
The router-id command is incorrectly referencing a physical interface; LDP may flap if GigabitEthernet0/0 goes down.
Using a physical interface as the LDP router ID is not recommended because if that interface fails, LDP sessions will reset. A loopback interface should be used for stability.
- B
Missing 'mpls label protocol ldp' under the interfaces will prevent LDP from running.
Why wrong: The 'mpls ip' command enables LDP on the interface by default; explicit 'mpls label protocol ldp' is not required.
- C
Cisco Express Forwarding (CEF) must be explicitly enabled globally; it is not enabled by default.
Why wrong: CEF is enabled by default on most IOS-XE images. The 'ip cef' command is shown, but even without it, MPLS requires CEF which is typically on.
- D
The configuration is correct and will work without any issues.
Why wrong: While it might work initially, using a physical interface as the LDP router ID is a design flaw that can cause instability.
Quick Answer
The answer is that the configuration incorrectly references a physical interface for the LDP router-id, which will cause LDP sessions to flap if that interface goes down. The `mpls ldp router-id` command is designed to use a stable IP address, typically from a loopback interface, because a loopback is always logically up and does not depend on the physical state of a link. Using a physical interface like GigabitEthernet0/0 ties the LDP identifier to a link that can fail, disrupting label exchange and potentially breaking MPLS forwarding. On the Cisco CCNP ENARSI 300-410 exam, this tests your understanding of MPLS LDP stability and the importance of loopback interfaces for control plane protocols; a common trap is assuming any interface works, but the exam expects you to recognize that physical interfaces introduce flapping risks. A solid memory tip is "Loopback for LDP—keep it up, keep it stable."
300-410 MPLS Operations Practice Question
This 300-410 practice question tests your understanding of mpls operations. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. 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.
Consider the following MPLS configuration on a Cisco router:
ip cef
!
interface GigabitEthernet0/0 ip address 192.168.1.1 255.255.255.252
mpls ip !
interface GigabitEthernet0/1 ip address 192.168.2.1 255.255.255.252
mpls ip ! mpls ldp router-id GigabitEthernet0/0
What is the likely 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 router-id command is incorrectly referencing a physical interface; LDP may flap if GigabitEthernet0/0 goes down.
The 'mpls ldp router-id' command expects a loopback interface or a stable IP address, not a physical interface name. Using a physical interface can cause LDP to flap if the interface goes down. Also, the command typically uses an interface's IP address, not the interface name directly. The correct syntax is 'mpls ldp router-id <interface> [force]', but it is best practice to use a loopback.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
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 router-id command is incorrectly referencing a physical interface; LDP may flap if GigabitEthernet0/0 goes down.
Why this is correct
Using a physical interface as the LDP router ID is not recommended because if that interface fails, LDP sessions will reset. A loopback interface should be used for stability.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Missing 'mpls label protocol ldp' under the interfaces will prevent LDP from running.
Why it's wrong here
The 'mpls ip' command enables LDP on the interface by default; explicit 'mpls label protocol ldp' is not required.
- ✗
Cisco Express Forwarding (CEF) must be explicitly enabled globally; it is not enabled by default.
Why it's wrong here
CEF is enabled by default on most IOS-XE images. The 'ip cef' command is shown, but even without it, MPLS requires CEF which is typically on.
- ✗
The configuration is correct and will work without any issues.
Why it's wrong here
While it might work initially, using a physical interface as the LDP router ID is a design flaw that can cause instability.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Command / output trap
The 'mpls ip' command enables LDP on the interface by default; explicit 'mpls label protocol ldp' is not required.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
- Use explanations to understand the rule behind the answer.
TExam Day Tips
- Underline the problem statement mentally.
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A practitioner preparing for the 300-410 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
Got this wrong? Here's your next step.
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
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FAQ
Questions learners often ask
What does this 300-410 question test?
MPLS Operations — This question tests MPLS Operations — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: The router-id command is incorrectly referencing a physical interface; LDP may flap if GigabitEthernet0/0 goes down. — The 'mpls ldp router-id' command expects a loopback interface or a stable IP address, not a physical interface name. Using a physical interface can cause LDP to flap if the interface goes down. Also, the command typically uses an interface's IP address, not the interface name directly. The correct syntax is 'mpls ldp router-id <interface> [force]', but it is best practice to use a loopback.
What should I do if I get this 300-410 question wrong?
Identify which 300-410 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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 →
Same concept, more angles
1 more ways this is tested on 300-410
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. Examine the following partial MPLS configuration on a Cisco IOS-XE router: interface GigabitEthernet0/0 ip address 10.0.1.1 255.255.255.252 mpls ip mpls label protocol ldp ! router ospf 1 network 10.0.1.0 0.0.0.3 area 0 ! mpls ldp router-id Loopback0 force What is the effect of this configuration?
medium- ✓ A.LDP will establish a session with the neighbor on GigabitEthernet0/0, using Loopback0 as the transport address.
- B.LDP will use the IP address of GigabitEthernet0/0 as the router ID because 'force' is not valid.
- C.LDP sessions will fail because OSPF is not redistributed into LDP.
- D.MPLS forwarding will not occur because 'mpls label protocol ldp' is redundant and causes a conflict.
Why A: The configuration enables LDP on the interface and globally via 'mpls ip'. The 'mpls label protocol ldp' is default but explicit. The 'mpls ldp router-id Loopback0 force' ensures LDP uses Loopback0 as the router ID, overriding any other interface. OSPF advertises the /30 link. This is a correct minimal MPLS configuration.
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Last reviewed: Jun 18, 2026
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