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CCNP Practice Question: A service provider uses MPLS L3VPN with OSPF as…
A service provider uses MPLS L3VPN with OSPF as the PE-CE routing protocol. A customer reports that a new subnet added on CE1 is not reachable from CE2, even though the PE1 router has the route in its VRF and BGP table. The 'show ip bgp vpnv4 vrf CUSTOMER' on PE2 shows the prefix with a valid next-hop. What should the engineer check next?
⚠ Common exam trap
Cisco often tests the distinction between control-plane reachability (BGP table) and data-plane forwarding (MPLS label switching), trapping candidates who assume that a route in the BGP table guarantees end-to-end connectivity.
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
✓
Verify that LDP has allocated a label for the BGP next-hop address on PE2.
The issue is that PE2 has the prefix in its BGP VPNv4 table with a valid next-hop, but the route is not reachable from CE2. This indicates a label-switching problem in the MPLS core. The next step is to verify that LDP has allocated a label for the BGP next-hop address on PE2, because without an LDP label for the next-hop, the MPLS forwarding path is broken and packets cannot be label-switched across the provider core.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Verify that LDP has allocated a label for the BGP next-hop address on PE2.
Why this is correct
Correct because without a label for the next-hop, the VPN route cannot be forwarded.
- ✗
Check if OSPF is redistributed into BGP on PE1.
Why it's wrong here
Incorrect because the route is already in BGP, so redistribution is working.
- ✗
Ensure the route is present in the global BGP table on PE2.
Why it's wrong here
Incorrect because the route is in the VPNv4 BGP table, which is sufficient.
- ✗
Confirm that the VRF on PE2 has the correct route-target import.
Why it's wrong here
Incorrect because the route is already in the VRF BGP table, so import is working.
Visual reference
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.
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JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 350-401 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 350-401 exam.