mediumMultiple ChoiceObjective-mapped
300-410 Practice Question: Consider the following MPLS configuration on a…
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.
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.
- ✗
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.
Visual reference
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Related to this question
Learn chapter
MPLS L3VPN Basics
Key term
MPLS Label Distribution
MPLS Label Distribution is the process by which routers exchange labels that tell them how to forward packets across a network without looking at the IP address each time.
Key term
LDP Protocol
LDP, or Label Distribution Protocol, is a protocol that routers use to automatically exchange labels that enable MPLS (Multiprotocol Label Switching) to create fast, efficient paths for data packets across a network.
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Same concept, more angles
1 more way 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.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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.