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CCNP Practice Question: An engineer is troubleshooting an MPLS VPN where…
An engineer is troubleshooting an MPLS VPN where CE1 (10.1.1.0/24) cannot reach CE2 (10.2.2.0/24). The PE routers are running OSPF with the CE routers. On PE1, the 'show ip route vrf CUSTOMER' output shows 10.2.2.0/24 as an OSPF route, but the prefix is not present in the global BGP table. What is the most likely cause?
⚠ Common exam trap
Cisco often tests the distinction between a route being present in the VRF routing table versus being present in the BGP table, trapping candidates who assume that OSPF-learned routes are automatically propagated across the MPLS VPN backbone without explicit redistribution into MP-BGP.
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
✓
Redistribution from OSPF into BGP under the VRF is not configured on PE1.
In an MPLS VPN, the PE router must redistribute OSPF routes learned from the CE into MP-BGP under the VRF to propagate them across the MPLS backbone. Without this redistribution, the prefix 10.2.2.0/24 appears in the VRF routing table as an OSPF route but is never injected into the BGP table, so it cannot be advertised to the remote PE. This explains why CE1 cannot reach CE2 despite the route being present locally on PE1.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Redistribution from OSPF into BGP under the VRF is not configured on PE1.
Why this is correct
Within an MPLS L3VPN, simply running OSPF in the VRF does not make a CE route available to the MP-BGP VPNv4 control plane. The PE must explicitly execute a redistribution command, such as 'redistribute ospf 1 vrf CUSTOMER' under 'router bgp AS ... address-family ipv4 vrf CUSTOMER'. Missing this command means the OSPF-installed route stays confined to the VRF RIB; it is never given a route distinguisher, tagged with an export route target, or sent to remote PEs. Consequently, even a healthy OSPF adjacency and populated VRF still result in no VPNv4 prefix.
- ✗
The OSPF adjacency between PE1 and CE1 is down.
Why it's wrong here
An OSPF adjacency failure would prevent the PE from learning CE routes in the first place, so the VRF routing table would not contain the missing prefix as an OSPF route. The scenario explicitly indicates the route is present in the VRF, which proves that the OSPF hello/DBD/LSU process has completed and the neighbor is in the Full state. Therefore, an adjacency-down condition cannot explain why an already-installed VRF route is absent from BGP.
- ✗
The VRF forwarding table on PE1 is full.
Why it's wrong here
A full VRF forwarding table is an FIB/CEF resource issue and would affect how packets are forwarded or whether a new route can be programmed into the data plane, not whether that route exists in the BGP VPNv4 table. In L3VPN operation, VPNv4 advertisement is driven by the VRF routing table and the redistribution policy under BGP, not by the size or capacity of the VRF forwarding table. If the route already appears in the VRF RIB, there is no capacity-related reason it cannot also be redistributed into BGP.
- ✗
MPLS LDP is not enabled on the PE1-CE1 link.
Why it's wrong here
LDP on the PE-CE link is nonsensical in a standard L3VPN design because LDP typically allocates labels for IGP routes across the MPLS core (P-to-P and PE-to-P interfaces), while the PE-to-CE link runs a plain IP routing protocol such as OSPF. VPNv4 prefixes are carried end-to-end in MP-BGP, which also allocates the inner VPN label; any core label needed for transport is handled by LDP or segment routing inside the service provider backbone. Missing LDP on the access link therefore has nothing to do with the failure to redistribute OSPF VRF routes into BGP on PE1.
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.