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300-410 Practice Question: Examine this MPLS configuration on a router: ip…
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.
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.
Why this is correct
If the specified router-id interface does not exist, LDP cannot determine its router ID and will not operate. A loopback must be created.
- ✗
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.
Quick reference
Routing Protocol Comparison
| Protocol | Metric | Max Hops | Algorithm | Type |
|---|---|---|---|---|
| RIP v2 | Hop count | 15 | Bellman-Ford | Distance vector |
| OSPF | Cost (bandwidth) | Unlimited | Dijkstra (SPF) | Link state |
| EIGRP | Composite metric | Unlimited | DUAL | Hybrid |
| IS-IS | Cost | Unlimited | Dijkstra | Link state |
| BGP | Policy / attributes | Unlimited | Path vector | Path vector |
RIP's 15-hop limit makes it unsuitable for large networks. OSPF and EIGRP dominate modern enterprise deployments.
Go deeper
Related to this question
Learn chapter
Introduction to ENARSI Exam and Network Fundamentals
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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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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