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300-410 Practice Question: Is troubleshooting an MPLS L3VPN where CE1…
A network engineer is troubleshooting an MPLS L3VPN where CE1 (10.1.1.0/24) cannot reach CE2 (10.2.2.0/24). The PE routers are using eBGP with the CEs. On PE1, the show ip bgp vpnv4 vrf CUSTOMER command shows the route for 10.2.2.0/24 with a next-hop of 192.168.1.2, and the show ip route vrf CUSTOMER command shows the route. However, traffic from CE1 to CE2 fails. The show ip bgp vpnv4 vrf CUSTOMER 10.2.2.0/24 command on PE1 shows the route is received and best, but the show ip bgp vpnv4 vrf CUSTOMER 10.2.2.0/24 command on PE1 also shows the route has the 'r' flag (RIB-failure). What is the most likely cause?
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
✓
There is a static route in the VRF for 10.2.2.0/24 with a lower administrative distance.
A RIB-failure indicates that the route is received and best in BGP but is not installed in the routing table because another route with a lower administrative distance exists. This could be due to a static route or an IGP route for the same prefix in the VRF.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
There is a static route in the VRF for 10.2.2.0/24 with a lower administrative distance.
Why this is correct
Correct: A static route or IGP route with lower AD will prevent the BGP route from being installed.
- ✗
The route-target import on PE1 is misconfigured.
Why it's wrong here
Incorrect because the route is received, so import is working.
- ✗
The MP-BGP session is not using the loopback interface.
Why it's wrong here
Incorrect because the route is received and best.
- ✗
The VRF on PE1 has a different route-target export.
Why it's wrong here
Incorrect because the route is received, indicating export is correct.
Go deeper
Related to this question
Learn chapter
Introduction to ENARSI Exam and Network Fundamentals
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.
Key term
MPLS Layer 3 VPN
A technology that uses Multiprotocol Label Switching to create secure, scalable virtual private networks that connect multiple sites at the network layer, where the service provider manages routing between customer sites.
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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.