Question 989 of 1,958
mediumMultiple ChoiceObjective-mapped
MPLS L3VPN: Troubleshooting VRF Route Advertisement to BGP
An engineer is configuring MPLS L3VPN on a Cisco IOS-XR router. The VRF CUSTOMER_B is configured with route-target import 100:1 and export 100:1. The engineer notices that the VRF routes are not being advertised to the route reflector. The BGP session to the route reflector is established and the VPNv4 address family is activated. What is the missing configuration?
Quick Answer
The missing configuration is the explicit activation of address-family ipv4 unicast vrf CUSTOMER_B under BGP with a redistribute command. This is required because in MPLS L3VPN on Cisco IOS-XR, VRF routes reside in the local routing table but are not automatically converted into VPNv4 prefixes for advertisement to the route reflector; the BGP process must be told to import those routes via redistribution. On the ENCOR 350-401 exam, this tests your understanding that a working VPNv4 session alone does not guarantee route propagation—a common trap is assuming VRF configuration is enough. Remember the sequence: VRF defines the routing table, BGP VPNv4 session provides the transport, but redistribution bridges the two. A useful memory tip is “VRF routes stay local until BGP is told to redistribute,” or think of it as needing to explicitly “invite” the VRF routes into the BGP conversation.
⚠ Common exam trap
Cisco often tests the misconception that configuring the VRF and establishing the BGP VPNv4 session is enough, but the trap is that candidates overlook the mandatory redistribution step under the VRF-specific BGP address family, which is required to inject routes into the VPNv4 table.
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 engineer did not configure the address-family ipv4 unicast vrf CUSTOMER_B under BGP and redistribute the routes.
In MPLS L3VPN on Cisco IOS-XR, simply configuring the VRF and establishing the BGP VPNv4 session is insufficient. The engineer must explicitly configure the address-family ipv4 unicast vrf CUSTOMER_B under BGP and use the redistribute command (e.g., redistribute connected or redistribute static) to inject the VRF routes into BGP for advertisement to the route reflector. Without this, the VRF routes remain in the local routing table but are never converted into VPNv4 prefixes.
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 VRF is not configured with a route distinguisher.
Why it's wrong here
Incorrect because a route distinguisher is required for VPNv4 routes, but the question states the routes are not being advertised; the RD might be missing, but that would cause a different error. However, the most common missing step is the BGP VRF configuration.
- ✓
The engineer did not configure the address-family ipv4 unicast vrf CUSTOMER_B under BGP and redistribute the routes.
Why this is correct
Correct because without this, the VRF routes are not injected into BGP VPNv4.
- ✗
The route-target import/export values are incorrect.
Why it's wrong here
Incorrect because route-targets affect route import/export on other PEs, not the advertisement from this PE.
- ✗
The interface in the VRF is not configured with the ipv4 address.
Why it's wrong here
Incorrect because the interface has an IP address, otherwise the VRF would not have any routes to advertise.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Same concept, more angles
1 more way this is tested on 350-401
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. A network engineer is configuring MPLS L3VPN on a Cisco IOS-XE PE router. The engineer creates a VRF named CUSTOMER_A with route-target import and export 100:1. After configuring the VRF on the interface connected to the CE router, the CE router can ping the PE's VRF interface IP, but cannot reach any remote VPNv4 routes. The BGP session between PE and route reflector is up. What is the most likely cause?
medium- A.The route-target import/export values are mismatched with the route reflector's configuration.
- ✓ B.The VRF is not activated under BGP using the address-family ipv4 vrf CUSTOMER_A command.
- C.The CE router is not configured with a default route pointing to the PE.
- D.The PE router needs the mpls ip command on the interface facing the CE router.
Why B: The CE router can ping the PE's VRF interface IP, confirming Layer 2 and VRF interface configuration are correct. However, the CE cannot reach remote VPNv4 routes, which indicates that the PE is not advertising or installing those routes into the VRF. The most likely cause is that the VRF CUSTOMER_A has not been activated under BGP using the 'address-family ipv4 vrf CUSTOMER_A' command, which is required to exchange IPv4 routes between the PE and CE within the VRF context and to redistribute them into MP-BGP for VPNv4 propagation.
Last reviewed: Jun 24, 2026
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.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.